ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 48,2022 Issue 6
indexed by
- Recommended Topics
- Current Issue
- Online First
- Archive
- Most Downloaded
Select AllDeselectExport
Display Method:
2022,48(6):665-676, DOI: 10.7519/j.issn.1000-0526.2021.090601
Abstract:
Global operational numerical models have the problem of occasional occurrences of extreme large medium-range forecast errors, and tracing these error sources could provide important references for improving the model itself and data assimilation system. In this study, errors of the operational forecasts in medium range (6 days) from the China Meteorological Administration high-resolution global assimilation and forecast system (CMA-GFS) and global ensemble prediction system (CMA-GEPS) with a lower resolution are analyzed during the period spanning from January to February 2020. The error origin for a particular case (initialized on 12 UTC 8 February 2020) with extreme large medium-range forecast errors over East Asia is investigated by employing the method of ensemble sensitivity analysis. From the spatial-temporal evolution characteristics of forecast errors in CMA-GFS and results from ensemble sensitivity analysis based on CMA-GEPS, a preliminary deduction was acquired about the key forecast error source region, i.e., an up-stream region of East Asia located in the Atlantic Ocean and western Europe (20°-90°N, 90°W-60°E). When the initial conditions of the control forecast of CMA-GEPS are replaced with that of the best ensemble member but confined to the above-mentioned key error source region, the medium-range forecast error of 500 hPa potential height was reduced greatly over East Asia, less than 50% of the original control forecast error. This further confirms the effectiveness of the identified key error source region.
Global operational numerical models have the problem of occasional occurrences of extreme large medium-range forecast errors, and tracing these error sources could provide important references for improving the model itself and data assimilation system. In this study, errors of the operational forecasts in medium range (6 days) from the China Meteorological Administration high-resolution global assimilation and forecast system (CMA-GFS) and global ensemble prediction system (CMA-GEPS) with a lower resolution are analyzed during the period spanning from January to February 2020. The error origin for a particular case (initialized on 12 UTC 8 February 2020) with extreme large medium-range forecast errors over East Asia is investigated by employing the method of ensemble sensitivity analysis. From the spatial-temporal evolution characteristics of forecast errors in CMA-GFS and results from ensemble sensitivity analysis based on CMA-GEPS, a preliminary deduction was acquired about the key forecast error source region, i.e., an up-stream region of East Asia located in the Atlantic Ocean and western Europe (20°-90°N, 90°W-60°E). When the initial conditions of the control forecast of CMA-GEPS are replaced with that of the best ensemble member but confined to the above-mentioned key error source region, the medium-range forecast error of 500 hPa potential height was reduced greatly over East Asia, less than 50% of the original control forecast error. This further confirms the effectiveness of the identified key error source region.
2022,48(6):677-690, DOI: 10.7519/j.issn.1000-0526.2022.040101
Abstract:
A local flash heavy rain process occurred in central Hebei Province in the evening of August 5, 2018, causing a flash flood and death of two people. The trigger and maintenance mechanisms of the flash heavy rain are analyzed using conventional observation data, ground automatic station data, NCEP reanalysis data, VDRAS data, FY-4 meteorological satellite and Doppler weather radar data. The results show that the flash heavy rain occurred under the control of the Western Pacific subtropical high at 500 hPa which was stronger and more northward than usual. Affected by the inverted trough of Typhoon Jongdari landing northward, the water vapor content above Hebei was abnormally abundant. The surface dew point temperature was as high as 28~29℃, and the atmospheric precipitable water deviated from the mean value by more than 4σ. In addition, the atmosphere was unstable and the environmental wind was weak, so the environmental conditions were conducive to the heavy rain. The physical processes leading to the torrential rain in three places in central Hebei were different. In the southeast of Bao-ding, the heavy rain was caused by the gust front moving southward and eastward to form a mesoscale convergence center, where thunderstorm cells merged, enhanced and propagated backward forming a quasi-stationary rain belt. The flash heavy rain in the west of Baoding was triggered by the enhancing easterly airflow in the boundary layer lifted by the windward slope of Taihang Mountain, where the echo maintained as a result of the cold pool formed by precipitation confronting with the easterly wind. The flash heavy rain in the northeast of Baoding experienced two stages: the north-south convective cloud belt and the east-west convective cloud belt, which was the heaviest precipitation at night. At 01:00 BT 6 August, the north-south convergence line formed by the south airflow strengthened at a low altitude (1500 m above the ground) on the east side of Baoding and the south airflow on the west side caused the north-south radar echo to develop. As the southeast airflow turned into a southerly airflow, the quasi-east-west-oriented warm shear line formed with the northeast airflow caused the echo to turn to east-west direction. The enhanced low-level south airflow at night dominated the strengthening and maintenance of the heavy rainfall echo in the northeastern part of Baoding, which was the key factor in determining the location of the flash heavy rain.
A local flash heavy rain process occurred in central Hebei Province in the evening of August 5, 2018, causing a flash flood and death of two people. The trigger and maintenance mechanisms of the flash heavy rain are analyzed using conventional observation data, ground automatic station data, NCEP reanalysis data, VDRAS data, FY-4 meteorological satellite and Doppler weather radar data. The results show that the flash heavy rain occurred under the control of the Western Pacific subtropical high at 500 hPa which was stronger and more northward than usual. Affected by the inverted trough of Typhoon Jongdari landing northward, the water vapor content above Hebei was abnormally abundant. The surface dew point temperature was as high as 28~29℃, and the atmospheric precipitable water deviated from the mean value by more than 4σ. In addition, the atmosphere was unstable and the environmental wind was weak, so the environmental conditions were conducive to the heavy rain. The physical processes leading to the torrential rain in three places in central Hebei were different. In the southeast of Bao-ding, the heavy rain was caused by the gust front moving southward and eastward to form a mesoscale convergence center, where thunderstorm cells merged, enhanced and propagated backward forming a quasi-stationary rain belt. The flash heavy rain in the west of Baoding was triggered by the enhancing easterly airflow in the boundary layer lifted by the windward slope of Taihang Mountain, where the echo maintained as a result of the cold pool formed by precipitation confronting with the easterly wind. The flash heavy rain in the northeast of Baoding experienced two stages: the north-south convective cloud belt and the east-west convective cloud belt, which was the heaviest precipitation at night. At 01:00 BT 6 August, the north-south convergence line formed by the south airflow strengthened at a low altitude (1500 m above the ground) on the east side of Baoding and the south airflow on the west side caused the north-south radar echo to develop. As the southeast airflow turned into a southerly airflow, the quasi-east-west-oriented warm shear line formed with the northeast airflow caused the echo to turn to east-west direction. The enhanced low-level south airflow at night dominated the strengthening and maintenance of the heavy rainfall echo in the northeastern part of Baoding, which was the key factor in determining the location of the flash heavy rain.
2022,48(6):691-704, DOI: 10.7519/j.issn.1000-0526.2021.123001
Abstract:
A rare extreme rainstorm occurred in Sichuan Basin on 21 May 2018. Both subjective and objective forecasts failed to capture this disastrous event. In this study, the large scale circulation, the triggering and developing mechanisms of mesoscale systems and the possible causes of forecast biases are analyzed based on the observational and reanalysis data. During this extreme rainstorm event, the westward extension of the western Pacific subtropical high and the abnormally strong Mongolia cold vortex jointly led to the southward invasion of the cold air. The water vapor and unstable energy in the southern Sichuan Basin were extremely stronger than normal, which favored the occurrence of convective heavy precipitation. The special topography near the Sichuan Basin was closely related to the triggering and maintaining of mesoscale convective systems. The northerly wind converged and was lifted up over the unique “bell mouth” terrain, forming a mesoscale convergence line and mesoscale low around the gorge. The temperature gradient on the west and south edges of the basin was increased due to the basin terrain and upwind heavy rainfall. Then, the ascending motion was induced in the large temperature gradient area. The persistent convergence of the northerly wind and the topographic obstruction made the convective systems move slowly, resulting in the increase of accumulated precipitation. However, the convections in the southern basin were mainly affected by the synoptic scale systems. The underestimate of convective precipitation by the EC model was possibly caused by the deviation of wind in the lower troposphere in the basin and the undetailed description of the basin terrain.
A rare extreme rainstorm occurred in Sichuan Basin on 21 May 2018. Both subjective and objective forecasts failed to capture this disastrous event. In this study, the large scale circulation, the triggering and developing mechanisms of mesoscale systems and the possible causes of forecast biases are analyzed based on the observational and reanalysis data. During this extreme rainstorm event, the westward extension of the western Pacific subtropical high and the abnormally strong Mongolia cold vortex jointly led to the southward invasion of the cold air. The water vapor and unstable energy in the southern Sichuan Basin were extremely stronger than normal, which favored the occurrence of convective heavy precipitation. The special topography near the Sichuan Basin was closely related to the triggering and maintaining of mesoscale convective systems. The northerly wind converged and was lifted up over the unique “bell mouth” terrain, forming a mesoscale convergence line and mesoscale low around the gorge. The temperature gradient on the west and south edges of the basin was increased due to the basin terrain and upwind heavy rainfall. Then, the ascending motion was induced in the large temperature gradient area. The persistent convergence of the northerly wind and the topographic obstruction made the convective systems move slowly, resulting in the increase of accumulated precipitation. However, the convections in the southern basin were mainly affected by the synoptic scale systems. The underestimate of convective precipitation by the EC model was possibly caused by the deviation of wind in the lower troposphere in the basin and the undetailed description of the basin terrain.
2022,48(6):705-718, DOI: 10.7519/j.issn.1000-0526.2022.030702
Abstract:
During 2-4 March 2021, a continuous low-cloud process in Beijing caused large deviation of temperature forecast. Both the global/regional numerical models and the forecasters failed to predict this process. Using the conventional meteorological data, ERA5 reanalysis data and FY-4A high-resolution visible cloud images, combined with the data of ceilometer and cloud radar, this paper discusses the formation and maintenance mechanism of the low cloud. The results are as follows. The favorable background for the formation of the low cloud was that there was no influence of obvious cold air after precipitation and the ground humidity was not well removed in the boundary layer. Meantime, the low cloud developed and maintained with stable atmospheric stratification, weak ascending motion and topographic effect. The warm advection and the growth of wind speed at 925 hPa destroyed the stable stratification, leading to the enhancement of mixing activity in the boundary layer and thus the dissipation of the low clouds. Detailed information of the cloud base height and cloud structure can be obtained via the ceilometer and cloud radar, which can be served as a useful complement to conventional observation.
During 2-4 March 2021, a continuous low-cloud process in Beijing caused large deviation of temperature forecast. Both the global/regional numerical models and the forecasters failed to predict this process. Using the conventional meteorological data, ERA5 reanalysis data and FY-4A high-resolution visible cloud images, combined with the data of ceilometer and cloud radar, this paper discusses the formation and maintenance mechanism of the low cloud. The results are as follows. The favorable background for the formation of the low cloud was that there was no influence of obvious cold air after precipitation and the ground humidity was not well removed in the boundary layer. Meantime, the low cloud developed and maintained with stable atmospheric stratification, weak ascending motion and topographic effect. The warm advection and the growth of wind speed at 925 hPa destroyed the stable stratification, leading to the enhancement of mixing activity in the boundary layer and thus the dissipation of the low clouds. Detailed information of the cloud base height and cloud structure can be obtained via the ceilometer and cloud radar, which can be served as a useful complement to conventional observation.
2022,48(6):719-728, DOI: 10.7519/j.issn.1000-0526.2022.051601
Abstract:
On April 12, 2020, affected by the cold vortex, a large-scale thunderstorm and gale occurred in East China, including an extreme gale exceeding the Beaufort scale 12 in Hangzhou Bay. Before the occurrence of this severe convection process, the high and low levels had consistent northwest air flow, with low water vapor content and weak energy conditions, so it was difficult to predict, thus larger deviations appeared in coastal sea surface wind forecast. Based on conventional observation data and Doppler weather radar and wind profile radar data, combined with ERA5 reanalysis data, this paper analyzes the characteristics of thunderstorm gale in this process and the evolution characteristics of convective system before and after its moving into Hangzhou Bay, and focuses on the possible causes of extreme gale in the northeast of Hangzhou Bay. The research shows that the formation of extremely strong wind in Hangzhou Bay was the result of the joint action of many factors. Hangzhou Bay had certain energy conditions, and the temperature reduction rate of the lower atmosphere was close to the dry adiabatic decline rate, which was conducive to the formation of strong downdraft in the convective system and the surface strong wind caused by subsidence divergence. There was a northwest wind jet in the middle layer. Under the action of convective subsidence, the high momentum in the middle layer was brought to the ground, enhancing the ground wind speed. During the process of the convective system moving towards Hangzhou Bay, the cold pool enhanced, and the friction on the water surface of Hangzhou Bay was smaller than that on land. Therefore, the intense flow in the cold pool spread faster, which was also one of the important reasons for the increasing of wind speed in Hangzhou Bay. The occurrence of gales above Beaufort scale 13 in the northeast of Hangzhou Bay was also related to the uneven distribution of marine thermal and dynamic conditions and the variation of echo shape after the convection moved into the sea.
On April 12, 2020, affected by the cold vortex, a large-scale thunderstorm and gale occurred in East China, including an extreme gale exceeding the Beaufort scale 12 in Hangzhou Bay. Before the occurrence of this severe convection process, the high and low levels had consistent northwest air flow, with low water vapor content and weak energy conditions, so it was difficult to predict, thus larger deviations appeared in coastal sea surface wind forecast. Based on conventional observation data and Doppler weather radar and wind profile radar data, combined with ERA5 reanalysis data, this paper analyzes the characteristics of thunderstorm gale in this process and the evolution characteristics of convective system before and after its moving into Hangzhou Bay, and focuses on the possible causes of extreme gale in the northeast of Hangzhou Bay. The research shows that the formation of extremely strong wind in Hangzhou Bay was the result of the joint action of many factors. Hangzhou Bay had certain energy conditions, and the temperature reduction rate of the lower atmosphere was close to the dry adiabatic decline rate, which was conducive to the formation of strong downdraft in the convective system and the surface strong wind caused by subsidence divergence. There was a northwest wind jet in the middle layer. Under the action of convective subsidence, the high momentum in the middle layer was brought to the ground, enhancing the ground wind speed. During the process of the convective system moving towards Hangzhou Bay, the cold pool enhanced, and the friction on the water surface of Hangzhou Bay was smaller than that on land. Therefore, the intense flow in the cold pool spread faster, which was also one of the important reasons for the increasing of wind speed in Hangzhou Bay. The occurrence of gales above Beaufort scale 13 in the northeast of Hangzhou Bay was also related to the uneven distribution of marine thermal and dynamic conditions and the variation of echo shape after the convection moved into the sea.
2022,48(6):729-745, DOI: 10.7519/j.issn.1000-0526.2022.040202
Abstract:
To understand more about the diversities of thunderstorm gust fronts, based on Doppler radar data from Tianjin and Cangzhou, wind profiler radar data from Xiqing and Huanghua, Tianjin Meteorological Tower, surface observations data, as well as VDRAS data, this paper comparatively analyzes the causes and correlation of two consecutive gust fronts that occurred in the Bohai Sea Bay on 10 June 2016. The results show that the structures are quite different between these two gust fronts. For the first gust front (GFⅠ), the near-surface meso-γ scale vortices tended to appear along the leading of GFⅠ, and the strong southwesterly warm-humid air flows from boundary layer and lower-level were transported to the thunderstorm along GFⅠ. For the second gust front (GF Ⅱ), dynamic structure was characterized by two strong inflows. One was boundary layer rear northeast inflow at 150-750 m height, another strong southwest inflow was at 990-2 190 m height. The two inflows induced two separated vertical clockwise circulations at the front and rear of GF Ⅱ. The configuration of cold pool and low-level vertical wind shear played an important role in formation and maintenance of these two gust fronts. The strength of cold pool at the rear of GFⅠ is relatively weak, and the 0-3 km vertical wind shear was stronger than the propagation speed of cold pool. The thunderstorm inclined to a stratiform cloud structure, which was not conducive to further development. Comparatively, for GF Ⅱ, the cold pool developed stronger, the propagation of cold pool was more than the 0-3 km vertical wind shear, thus the updraft in the thunderstorm was more vertical, resulting in intensified storm. Meanwhile, the interaction and inherent correlation between meso-γ scale vortex and cold pool were also obvious. Due to the collision of meso-γ scale vortices, strong low-level convergence and updraft occurred between the two front gusts. Moreover, the consolidation of the two cold pools aggravated low-layer instability, which increased the rotation of the upper and lower layers, and formed strong horizontal vorticity, finally leading to the rapid strengthening of convective storm and evolution into bow echo.
To understand more about the diversities of thunderstorm gust fronts, based on Doppler radar data from Tianjin and Cangzhou, wind profiler radar data from Xiqing and Huanghua, Tianjin Meteorological Tower, surface observations data, as well as VDRAS data, this paper comparatively analyzes the causes and correlation of two consecutive gust fronts that occurred in the Bohai Sea Bay on 10 June 2016. The results show that the structures are quite different between these two gust fronts. For the first gust front (GFⅠ), the near-surface meso-γ scale vortices tended to appear along the leading of GFⅠ, and the strong southwesterly warm-humid air flows from boundary layer and lower-level were transported to the thunderstorm along GFⅠ. For the second gust front (GF Ⅱ), dynamic structure was characterized by two strong inflows. One was boundary layer rear northeast inflow at 150-750 m height, another strong southwest inflow was at 990-2 190 m height. The two inflows induced two separated vertical clockwise circulations at the front and rear of GF Ⅱ. The configuration of cold pool and low-level vertical wind shear played an important role in formation and maintenance of these two gust fronts. The strength of cold pool at the rear of GFⅠ is relatively weak, and the 0-3 km vertical wind shear was stronger than the propagation speed of cold pool. The thunderstorm inclined to a stratiform cloud structure, which was not conducive to further development. Comparatively, for GF Ⅱ, the cold pool developed stronger, the propagation of cold pool was more than the 0-3 km vertical wind shear, thus the updraft in the thunderstorm was more vertical, resulting in intensified storm. Meanwhile, the interaction and inherent correlation between meso-γ scale vortex and cold pool were also obvious. Due to the collision of meso-γ scale vortices, strong low-level convergence and updraft occurred between the two front gusts. Moreover, the consolidation of the two cold pools aggravated low-layer instability, which increased the rotation of the upper and lower layers, and formed strong horizontal vorticity, finally leading to the rapid strengthening of convective storm and evolution into bow echo.
2022,48(6):746-759, DOI: 10.7519/j.issn.1000-0526.2021.122401
Abstract:
The 2012-2020 surface observation and sounding data from Beijing Meteorological Observatory, Zhangjiakou Station and Laoting Station in winter as well as other data are used to establish a set of discrimination criteria for different precipitation types by statistically analyzing vertical temperature and humidity profiles. From forecast perspective, we focus on two key factors of snowflakes forming and melting, and adopt the cloud-top temperature and the 0℃-layer height as new indicators of discrimination criteria for precipitation types. The results show that cloud-top temperature below or equal to -14℃ is a key threshold to generate adequate snowflakes or other ice particles in clouds. This is a necessary condition for snowfall. At the same time, the 0℃-layer height higher than or equal to 0.5 km and lower than or equal to 0.1 km is a threshold for the snowflakes to hardly melt and completely melt, respectively. Sleet or rain is likely to appear with cloud top-temperature between -14℃ and -4℃. The 0℃-layer height at 0.1 km is a threshold of distinguishing sleet from rain. The TS scores of discrimination criteria based on cloud-top temperature and 0℃-layer height in this paper are significantly improved compared with those by using the combination of temperatures at specific layers. The TS scores for snow, sleet and rain reach (improved) 0.93 (0.11), 0.57 (0.39) and 0.86 (0.43), respectively. The results of this study could provide a new reference for forecast and amendment of winter precipitation type.
The 2012-2020 surface observation and sounding data from Beijing Meteorological Observatory, Zhangjiakou Station and Laoting Station in winter as well as other data are used to establish a set of discrimination criteria for different precipitation types by statistically analyzing vertical temperature and humidity profiles. From forecast perspective, we focus on two key factors of snowflakes forming and melting, and adopt the cloud-top temperature and the 0℃-layer height as new indicators of discrimination criteria for precipitation types. The results show that cloud-top temperature below or equal to -14℃ is a key threshold to generate adequate snowflakes or other ice particles in clouds. This is a necessary condition for snowfall. At the same time, the 0℃-layer height higher than or equal to 0.5 km and lower than or equal to 0.1 km is a threshold for the snowflakes to hardly melt and completely melt, respectively. Sleet or rain is likely to appear with cloud top-temperature between -14℃ and -4℃. The 0℃-layer height at 0.1 km is a threshold of distinguishing sleet from rain. The TS scores of discrimination criteria based on cloud-top temperature and 0℃-layer height in this paper are significantly improved compared with those by using the combination of temperatures at specific layers. The TS scores for snow, sleet and rain reach (improved) 0.93 (0.11), 0.57 (0.39) and 0.86 (0.43), respectively. The results of this study could provide a new reference for forecast and amendment of winter precipitation type.
2022,48(6):760-772, DOI: 10.7519/j.issn.1000-0526.2022.032103
Abstract:
According to the actual performance characteristics of the millimeter wave cloud measuring radar in Pinghe Area of Fujian Province, and in response to the problem of range sidelobe artifacts in operation, an improved data quality control method is proposed. Using the observation data in Pinghe of Fujian Province from September 2018 to August 2020, the quality of the radar is quantitatively evaluated to study the actual impact of data quality control on cloud-precipitation detection. The results show that the proposed method can well improve the radar detection measurements, and the range sidelobe artifacts can be effectively filtered. The range sidelobe also significantly affect the radar’s detection of airborne cloud and rain echoes. The impact is most concentrated near the starting height above the blind zone of the two wide pulse modes, namely 1.50-2.28 km and 3.63-7.74 km, and the frequency of range sidelobe artifact decreases as altitude increases. The range sidelobe artifact mainly interferes with radar detection of low and medium level weak clouds, thus leading to underestimation of cloud base and overestimation of cloud top and cloud thickness. The average errors of three cloud parameters can reach -0.53、0.74 and 0.73 km respectively.
According to the actual performance characteristics of the millimeter wave cloud measuring radar in Pinghe Area of Fujian Province, and in response to the problem of range sidelobe artifacts in operation, an improved data quality control method is proposed. Using the observation data in Pinghe of Fujian Province from September 2018 to August 2020, the quality of the radar is quantitatively evaluated to study the actual impact of data quality control on cloud-precipitation detection. The results show that the proposed method can well improve the radar detection measurements, and the range sidelobe artifacts can be effectively filtered. The range sidelobe also significantly affect the radar’s detection of airborne cloud and rain echoes. The impact is most concentrated near the starting height above the blind zone of the two wide pulse modes, namely 1.50-2.28 km and 3.63-7.74 km, and the frequency of range sidelobe artifact decreases as altitude increases. The range sidelobe artifact mainly interferes with radar detection of low and medium level weak clouds, thus leading to underestimation of cloud base and overestimation of cloud top and cloud thickness. The average errors of three cloud parameters can reach -0.53、0.74 and 0.73 km respectively.
2022,48(6):773-782, DOI: 10.7519/j.issn.1000-0526.2022.033001
Abstract:
Based on rotated empirical orthogonal function analysis of the daily observational data of visibility from 2008 to 2018, the objective division of visibility in different seasons is obtained. Taking the global numerical prediction model of ECMWF from 2017 to 2019 as the prediction factor, the visibility prediction model for different regions and seasons is built and the regional model is applied to the station for prediction. Then the ECMWF model forecast data in 2020 are used as an independent sample, and the seasonal forecast of visibility in China is carried out. The results show that using the comprehensive algorithm of multiple linear regression, regression estimate of event possibility and discriminant analysis, the visibility forecast of model output statistics based on regional model output statistics is much better in different seasons and different forecast projections than the model direct output (DMO). The underestimation of DMO is corrected, and the improvement of winter forecast score is the most obvious. The model shows high prediction skills in the prediction of low visibility below 1 km, especially at 05:00 BT. Factor analysis shows the high-frequency factors affecting visibility mainly include temperature, pressure, humidity and wind that are closely related to boundary layer conditions, as well as surface thermal conditions, precipitation related factors and stability. The high-frequency factors selected for visibility prediction of different orders in different seasons are different. Spring is sensitive to temperature-related factors, the factors related to precipitation are selected more frequently in summer， and the unstable factors in autumn and winter are more important.
Based on rotated empirical orthogonal function analysis of the daily observational data of visibility from 2008 to 2018, the objective division of visibility in different seasons is obtained. Taking the global numerical prediction model of ECMWF from 2017 to 2019 as the prediction factor, the visibility prediction model for different regions and seasons is built and the regional model is applied to the station for prediction. Then the ECMWF model forecast data in 2020 are used as an independent sample, and the seasonal forecast of visibility in China is carried out. The results show that using the comprehensive algorithm of multiple linear regression, regression estimate of event possibility and discriminant analysis, the visibility forecast of model output statistics based on regional model output statistics is much better in different seasons and different forecast projections than the model direct output (DMO). The underestimation of DMO is corrected, and the improvement of winter forecast score is the most obvious. The model shows high prediction skills in the prediction of low visibility below 1 km, especially at 05:00 BT. Factor analysis shows the high-frequency factors affecting visibility mainly include temperature, pressure, humidity and wind that are closely related to boundary layer conditions, as well as surface thermal conditions, precipitation related factors and stability. The high-frequency factors selected for visibility prediction of different orders in different seasons are different. Spring is sensitive to temperature-related factors, the factors related to precipitation are selected more frequently in summer， and the unstable factors in autumn and winter are more important.
2022,48(6):783-793, DOI: 10.7519/j.issn.1000-0526.2022.040801
Abstract:
The drought occurred in autumn， winter and spring in South China from October 2020 to May 2021， especially in Guangdong, where the duration of drought and the degree of precipitation reduction were rare in recent 58 years. Using the daily precipitation and temperature data of 86 national meteorological stations in Guangdong， NCEP/NCAR and NOAA reanalysis data， this paper studies the abnormal characteristics of atmospheric circulation and SST in autumn， winter and spring in Guangdong from 2020 to 2021 by using correlation and synthesis analysis methods， and discusses its relationship with the drought in autumn， winter and spring in Guangdong. The results show that the drought in autumn， winter and spring in Guangdong from 2020 to 2021 occurred under the climate background of less precipitation， and was closely related to the anomalies of atmospheric circulation and SST. In the autumn， winter and spring of 2020-2021， the high-level subtropical westerly jet in the Northern Hemisphere was weakened， the southern section of the Middle East Asia trough was significantly weakened， the ridge line of the Western Pacific subtropical high was significantly northward， the low level south branch trough was weak， the cold air affecting Guangdong was weak， Guangdong is in the water vapor divergence area， and the North Pacific high pressure was significantly enhanced. A La Ni〖AKn~D〗a event with moderate intensity occurred in the equatorial Middle East Pacific from August 2020 to March 2021， the atmosphere responded significantly to the La Ni〖AKn~D〗a event， the Walker circulation strengthened， the upward movement near the Philippines was obvious， and there was a downward movement in Guangdong, so that a cyclonic abnormal circulation formed near the tropical Western Pacific， the South China Sea and the Philippines in the lower troposphere. The cyclonic abnormal circlution blocked the transport of southwest water vapor from the Bay of Bengal and the South China Sea to Guangdong. At the same time， the temperature was significantly higher. At last, the high temperature and less rain led to the occurrence of drought in Guangdong.
The drought occurred in autumn， winter and spring in South China from October 2020 to May 2021， especially in Guangdong, where the duration of drought and the degree of precipitation reduction were rare in recent 58 years. Using the daily precipitation and temperature data of 86 national meteorological stations in Guangdong， NCEP/NCAR and NOAA reanalysis data， this paper studies the abnormal characteristics of atmospheric circulation and SST in autumn， winter and spring in Guangdong from 2020 to 2021 by using correlation and synthesis analysis methods， and discusses its relationship with the drought in autumn， winter and spring in Guangdong. The results show that the drought in autumn， winter and spring in Guangdong from 2020 to 2021 occurred under the climate background of less precipitation， and was closely related to the anomalies of atmospheric circulation and SST. In the autumn， winter and spring of 2020-2021， the high-level subtropical westerly jet in the Northern Hemisphere was weakened， the southern section of the Middle East Asia trough was significantly weakened， the ridge line of the Western Pacific subtropical high was significantly northward， the low level south branch trough was weak， the cold air affecting Guangdong was weak， Guangdong is in the water vapor divergence area， and the North Pacific high pressure was significantly enhanced. A La Ni〖AKn~D〗a event with moderate intensity occurred in the equatorial Middle East Pacific from August 2020 to March 2021， the atmosphere responded significantly to the La Ni〖AKn~D〗a event， the Walker circulation strengthened， the upward movement near the Philippines was obvious， and there was a downward movement in Guangdong, so that a cyclonic abnormal circulation formed near the tropical Western Pacific， the South China Sea and the Philippines in the lower troposphere. The cyclonic abnormal circlution blocked the transport of southwest water vapor from the Bay of Bengal and the South China Sea to Guangdong. At the same time， the temperature was significantly higher. At last, the high temperature and less rain led to the occurrence of drought in Guangdong.
2022,48(6):794-800, DOI: 10.7519/j.issn.1000-0526.2022.051001
Abstract:
The main characteristics of the general atmospheric circulation in March 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere. The 500 hPa geopotential height presented the distribution of an anomalous four-wave pattern in the mid-high latitude of Northern Hemisphere and the air flow was straight in Asia. The strength of Western Pacific subtropical high was a little higher than that in normal years, and the south branch trough was a little weaker. There was only one strong cold front process in March. The national average temperature in March was 7.2℃, 2.4℃ higher than the normal and recorded the first in the same period since 1961. The monthly mean precipitation amount was 36.7 mm, 25% more than in normal period (29.4 mm). Three rainfall processes occurred in this month, causing severe weather such as heavy rain and thunderstorm. In addition, there were two large-scale sand-dust weather processes in northern China. Droughts appeared and developed in Huanghuai Region and Jianghuai Region.
The main characteristics of the general atmospheric circulation in March 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere. The 500 hPa geopotential height presented the distribution of an anomalous four-wave pattern in the mid-high latitude of Northern Hemisphere and the air flow was straight in Asia. The strength of Western Pacific subtropical high was a little higher than that in normal years, and the south branch trough was a little weaker. There was only one strong cold front process in March. The national average temperature in March was 7.2℃, 2.4℃ higher than the normal and recorded the first in the same period since 1961. The monthly mean precipitation amount was 36.7 mm, 25% more than in normal period (29.4 mm). Three rainfall processes occurred in this month, causing severe weather such as heavy rain and thunderstorm. In addition, there were two large-scale sand-dust weather processes in northern China. Droughts appeared and developed in Huanghuai Region and Jianghuai Region.
Select AllDeselectExport
Display Method:
Available online: June 24, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.051102
Abstract:
In view of the comprehensive evaluation on the forecast performance of disastrous heavy precipitation concerned by power grid industry, and by referring to the test of the effect of professional meteorological service of heavy precipitation in the main flood season (June-September, 2019) in Beijing-Tianjin-Hebei region, the paper has carried out in-depth analysis on using MODE (Method for Object-based Diagnostic Evaluation) in the inspection of short-term and impending forecast from two aspects, namely, target recognition of precipitation and target matching of precipitation. The results have shown that the heavy precipitations in the main flood season of Beijing-Tianjin-Hebei region were mainly concentrated from afternoon to the first half of the night, which were characterized by heavy in amount, small in range, easy false-alarms, and difficulty in predicting their spatial characteristics; The correlation coefficient of diurnal variation of the heavy precipitation frequency of short-term and impending forecast ranged from 0.78 to 0.94, while that of the diurnal variation of range was from 0.6 to 0.82. The forecast effect of moving path and rainfall intensity was slightly better than that of the falling area. The shorter the forecast time, the better the forecast effect of heavy precipitations and their spatial characteristics; The comprehensive forecast evaluation method put forward in the paper can make up for the shortcomings of traditional inspection methods, which can explore the potential and limitations of forecast, and provide reference for accurate and specialized meteorological services.
In view of the comprehensive evaluation on the forecast performance of disastrous heavy precipitation concerned by power grid industry, and by referring to the test of the effect of professional meteorological service of heavy precipitation in the main flood season (June-September, 2019) in Beijing-Tianjin-Hebei region, the paper has carried out in-depth analysis on using MODE (Method for Object-based Diagnostic Evaluation) in the inspection of short-term and impending forecast from two aspects, namely, target recognition of precipitation and target matching of precipitation. The results have shown that the heavy precipitations in the main flood season of Beijing-Tianjin-Hebei region were mainly concentrated from afternoon to the first half of the night, which were characterized by heavy in amount, small in range, easy false-alarms, and difficulty in predicting their spatial characteristics; The correlation coefficient of diurnal variation of the heavy precipitation frequency of short-term and impending forecast ranged from 0.78 to 0.94, while that of the diurnal variation of range was from 0.6 to 0.82. The forecast effect of moving path and rainfall intensity was slightly better than that of the falling area. The shorter the forecast time, the better the forecast effect of heavy precipitations and their spatial characteristics; The comprehensive forecast evaluation method put forward in the paper can make up for the shortcomings of traditional inspection methods, which can explore the potential and limitations of forecast, and provide reference for accurate and specialized meteorological services.
Available online: June 24, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050502
Abstract:
In this study, based on the method for object-based diagnostic evaluation and the hourly precipitation data from the CMADaas（China Meteorological Administration Data as a server）, the forecast performances of three numerical models during the main flood seasons from 2019 to 2020 in Liaoning Province are investigated, including the Shanghai Numerical Prediction Model of China Meteorological Administration (CMA-SH9), the Mesoscale Weather Numerical Prediction System of China Meteorological Administration (CMA-MESO) and the Rapid-refresh Multi-scale Analysis and Prediction System-Northeast China Model (CMA-DB). The results show that even for the kilometer-scale or near-kilometer-scale models, there are still obvious deviations in the forecast of the heavy rainfall area (12-hour cumulative rainfall ≥ 50 mm) within the 36-hour forecast leading time. The ratio of overlapping area between the forecasted and observed heavy rainfall areas is generally less than 10% of the total area, and in individual cases the value is close to 20%, such as the forecast of CMA-MESO on cyclone-type precipitation processes. The deviation of rainfall area results in a high missing alarm rate (MAR) (generally around 75%, and the MAR of the CMA-MESO is 10%–20% lower than that). The MAR of heavy precipitation forecast for the rear of high-pressure type precipitation exceeds 80%. Besides, the deviation of heavy rainfall area also results in a higher false alarm rate (FAR). For the forecast of short-term heavy rainfall (1-hour rainfall ≥ 20 mm), by analyzing the mean values of the statistical indexes within 12 h forecast leading time, we find that the average percentage of detection is below 10%, with the maximum value being only 9.2%. The average FAR is 58.7%. Note that, in the above statistics if the location difference between forecast and observation is less than 40 km, it is counted as a correct forecast. Among the three types of rainfall processes, the model has the poorest performance in the forecast of short-term heavy rainfall in typhoon-type rainfall processes.
In this study, based on the method for object-based diagnostic evaluation and the hourly precipitation data from the CMADaas（China Meteorological Administration Data as a server）, the forecast performances of three numerical models during the main flood seasons from 2019 to 2020 in Liaoning Province are investigated, including the Shanghai Numerical Prediction Model of China Meteorological Administration (CMA-SH9), the Mesoscale Weather Numerical Prediction System of China Meteorological Administration (CMA-MESO) and the Rapid-refresh Multi-scale Analysis and Prediction System-Northeast China Model (CMA-DB). The results show that even for the kilometer-scale or near-kilometer-scale models, there are still obvious deviations in the forecast of the heavy rainfall area (12-hour cumulative rainfall ≥ 50 mm) within the 36-hour forecast leading time. The ratio of overlapping area between the forecasted and observed heavy rainfall areas is generally less than 10% of the total area, and in individual cases the value is close to 20%, such as the forecast of CMA-MESO on cyclone-type precipitation processes. The deviation of rainfall area results in a high missing alarm rate (MAR) (generally around 75%, and the MAR of the CMA-MESO is 10%–20% lower than that). The MAR of heavy precipitation forecast for the rear of high-pressure type precipitation exceeds 80%. Besides, the deviation of heavy rainfall area also results in a higher false alarm rate (FAR). For the forecast of short-term heavy rainfall (1-hour rainfall ≥ 20 mm), by analyzing the mean values of the statistical indexes within 12 h forecast leading time, we find that the average percentage of detection is below 10%, with the maximum value being only 9.2%. The average FAR is 58.7%. Note that, in the above statistics if the location difference between forecast and observation is less than 40 km, it is counted as a correct forecast. Among the three types of rainfall processes, the model has the poorest performance in the forecast of short-term heavy rainfall in typhoon-type rainfall processes.
Available online: June 16, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.042102
Abstract:
In order to meet the local actual business and service needs, we selected the 0.05°×0.05°national-level grid forecast guidance products issued by the china Meteorological administration and the CMA Land Data Assimilation System (CLDAS) hourly live data, using three types of The Average filtering method revised the 240h of spring per 3h temperature forecast products in the northern Xinjiang plain area, which compared and verified the forecast effects of four forecast products after the correction. The test results show that the accuracy and stability of the temperature and frost forecasts are significantly improved after the filtering method is corrected. compared with the national grid forecast guidance products, the three revised forecast products have reduced the average temperature mean square error by 0.79?℃、0.85?℃, and 0.88 ℃ in the results of the time-dependent inspection, and the accuracy of the temperature forecast has increased by 6.11 %, 6.38 %, and 6.46 %on average. the accuracy of frost forecasting increased by 3，5.81，7.31 on average, and the root mean square error of the daily duration of frost forecasting decreased by 4.21h, 4.41h, and 4.35h. In the sub-regional test results, the root mean square error of temperature was reduced by 0.66 ℃, 0.71 ℃, 0.9 ℃, and the accuracy of temperature forecasting was increased by 5.7 %, 6.1 %, and 6.1 %. The accuracy of frost forecasting was in the area of 600-1200 meters above sea level. Increased by 2.5, 4.8, 5.4，no increase in other regions. The root mean square error of the daily duration of frost forecast decreased by 0.81h, 0.63h, and 0.56h on average. In comparison, the optimal integrated method has the best correction effect.
In order to meet the local actual business and service needs, we selected the 0.05°×0.05°national-level grid forecast guidance products issued by the china Meteorological administration and the CMA Land Data Assimilation System (CLDAS) hourly live data, using three types of The Average filtering method revised the 240h of spring per 3h temperature forecast products in the northern Xinjiang plain area, which compared and verified the forecast effects of four forecast products after the correction. The test results show that the accuracy and stability of the temperature and frost forecasts are significantly improved after the filtering method is corrected. compared with the national grid forecast guidance products, the three revised forecast products have reduced the average temperature mean square error by 0.79?℃、0.85?℃, and 0.88 ℃ in the results of the time-dependent inspection, and the accuracy of the temperature forecast has increased by 6.11 %, 6.38 %, and 6.46 %on average. the accuracy of frost forecasting increased by 3，5.81，7.31 on average, and the root mean square error of the daily duration of frost forecasting decreased by 4.21h, 4.41h, and 4.35h. In the sub-regional test results, the root mean square error of temperature was reduced by 0.66 ℃, 0.71 ℃, 0.9 ℃, and the accuracy of temperature forecasting was increased by 5.7 %, 6.1 %, and 6.1 %. The accuracy of frost forecasting was in the area of 600-1200 meters above sea level. Increased by 2.5, 4.8, 5.4，no increase in other regions. The root mean square error of the daily duration of frost forecast decreased by 0.81h, 0.63h, and 0.56h on average. In comparison, the optimal integrated method has the best correction effect.
Available online: June 13, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.051101
Abstract:
Based on the conventional high altitude and surface observation data, NCEP reanalysis data and radar data, this paper analyzed the mechanism and evolution characteristics of convection initiation under the influence of cold air in Suizhou and Jingzhou areas of Hubei Province on 4 May 2020. The results showed that there were three initiation processes of severe convection in Suizhou area, including warm sector convergence process, cold front process and low-level jet process. At the same time, the special topography of Suizhou plays an important role in the maintenance of severe convection. The condition of convective initiation under the influence of cold air is related to the thickness of the cold air and the level of free convection. When the convergence level of cold air and warm moisture flow is higher than the free convection level, and the convergence has a certain vertical thickness, it is more likely to be convection initiation. The cold air intensity in Suizhou is stronger than that in Jingzhou, and the front at lower tropospheric level is robust, the updraft in the middle and east area of the positive potential vorticity anomaly is strong, which favored convection initiation. However, there is no convective initiation in Jingzhou, because the lower tropospheric front is weak, as well as the intensity of cold air and the updraft.
Based on the conventional high altitude and surface observation data, NCEP reanalysis data and radar data, this paper analyzed the mechanism and evolution characteristics of convection initiation under the influence of cold air in Suizhou and Jingzhou areas of Hubei Province on 4 May 2020. The results showed that there were three initiation processes of severe convection in Suizhou area, including warm sector convergence process, cold front process and low-level jet process. At the same time, the special topography of Suizhou plays an important role in the maintenance of severe convection. The condition of convective initiation under the influence of cold air is related to the thickness of the cold air and the level of free convection. When the convergence level of cold air and warm moisture flow is higher than the free convection level, and the convergence has a certain vertical thickness, it is more likely to be convection initiation. The cold air intensity in Suizhou is stronger than that in Jingzhou, and the front at lower tropospheric level is robust, the updraft in the middle and east area of the positive potential vorticity anomaly is strong, which favored convection initiation. However, there is no convective initiation in Jingzhou, because the lower tropospheric front is weak, as well as the intensity of cold air and the updraft.
Available online: June 10, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.053001
Abstract:
Based on the operational real-time typhoon data of National Meteorological Center and other sources of observations including automatic station and satellite images, the main characteristics of typhoon activities in western North Pacific and the South China Sea in 2021, including influential TCs tracks , intensity, wind and rainfall, were analyzed and reviewed. In 2021, the genesis region is obviously westward, with 5 TCs generated in the SCS. The overall intensity of TCs are weaker than normal, 6 TCs experienced rapid intensification activities, among them Chathu increased by 40 m/s within 24 hours, which was rare in the past 30 yr. There are 6 TCs made landfall in China and 2 others affected coastal areas.The forecast error analysis shows that the main intensity forecast error comes from the rapid intensification cases, while the track forecast error is mainly caused by the sharp turning .Under the weak steering flow, the northward movement of Typhoon In-Fa after slowing down was related to the influence of upper-tropospheric cold low (UTCL).The increase of nearshore deep convection caused by land-sea thermal difference and local convergence could be the main reason for the offshore rapid intensification of Cempaka.Under the background of the obvious adjustment of the subtropical high, Chanthu circled over the northern part of the East China Sea for 3 days still brought obvious rainfall and gale winds to the east China.
Based on the operational real-time typhoon data of National Meteorological Center and other sources of observations including automatic station and satellite images, the main characteristics of typhoon activities in western North Pacific and the South China Sea in 2021, including influential TCs tracks , intensity, wind and rainfall, were analyzed and reviewed. In 2021, the genesis region is obviously westward, with 5 TCs generated in the SCS. The overall intensity of TCs are weaker than normal, 6 TCs experienced rapid intensification activities, among them Chathu increased by 40 m/s within 24 hours, which was rare in the past 30 yr. There are 6 TCs made landfall in China and 2 others affected coastal areas.The forecast error analysis shows that the main intensity forecast error comes from the rapid intensification cases, while the track forecast error is mainly caused by the sharp turning .Under the weak steering flow, the northward movement of Typhoon In-Fa after slowing down was related to the influence of upper-tropospheric cold low (UTCL).The increase of nearshore deep convection caused by land-sea thermal difference and local convergence could be the main reason for the offshore rapid intensification of Cempaka.Under the background of the obvious adjustment of the subtropical high, Chanthu circled over the northern part of the East China Sea for 3 days still brought obvious rainfall and gale winds to the east China.
LI Lan-yu, Luo Bin, WANG Bo, LI Yan-lin, WANG Shun-xia, XU Sheng-gang, LI Sheng, ZHOU Ji, NIU Jing-ping
Available online: June 08, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.060101
Abstract:
With the data of daily outpatient visits of allergic rhinitis, air pollution and meteorological data in Lanzhou (2014—2016), Tianshui (2016—2018), and Zhangye (2016—2018), this study estimated the relationship between relative humidity (RH), absolute humidity (AH) and the daily outpatient visits of allergic rhinitis. In these three cities, the peak period of daily outpatient visits for allergic rhinitis was from August to September. The decrease in RH could lead to significant increase in outpatient visits for allergic rhinitis in these 3 cities. With the each 1% decrease of RH, the outpatients visit for allergic rhinitis in Lanzhou, Tianshui and Zhangye could increase by 1.36%, 2.30% and 1.50%, respectively, which were 14.92 %, 16.00% and 13.98% for each 1g·m-3 decrease in AH. Our study suggested that the onset of allergic rhinitis is negatively associated with atmospheric environmental humidity, and the dry and low-humidity environment is an important risk factor for allergic rhinitis in arid area. Compared with RH, AH may be better to reflect the effects of environmental humidity on allergic rhinitis.
With the data of daily outpatient visits of allergic rhinitis, air pollution and meteorological data in Lanzhou (2014—2016), Tianshui (2016—2018), and Zhangye (2016—2018), this study estimated the relationship between relative humidity (RH), absolute humidity (AH) and the daily outpatient visits of allergic rhinitis. In these three cities, the peak period of daily outpatient visits for allergic rhinitis was from August to September. The decrease in RH could lead to significant increase in outpatient visits for allergic rhinitis in these 3 cities. With the each 1% decrease of RH, the outpatients visit for allergic rhinitis in Lanzhou, Tianshui and Zhangye could increase by 1.36%, 2.30% and 1.50%, respectively, which were 14.92 %, 16.00% and 13.98% for each 1g·m-3 decrease in AH. Our study suggested that the onset of allergic rhinitis is negatively associated with atmospheric environmental humidity, and the dry and low-humidity environment is an important risk factor for allergic rhinitis in arid area. Compared with RH, AH may be better to reflect the effects of environmental humidity on allergic rhinitis.
Available online: June 02, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.042201
Abstract:
Scientific and reasonable disaster indexes are the basis and key to the effective disaster early warning and accurate disaster impact assessment. In this study, based on the disaster-causing principle of wind, the wind disaster indexes of facility agriculture were divided into two levels. The level Ⅰ was for damage to the main structure of the facility, level II was for damage to the shed film. Based on the local climate characteristics and design service life of solar greenhouses and plastic tunnels, the extreme value probability distribution model was used to analyze the maximum wind speed observation data of 2467 weather stations from 1989 to 2018, and the maximum wind speed of 20a and 10a return period were calculated. On this basis, the wind resistance of different types of facilities and the disaster-causing factors were considered, and the wind disaster indexes for solar greenhouses and plastic tunnels of different levels based on extreme wind speed were established. According to the main distribution areas of solar greenhouses and plastic tunnels in China, the wind disaster indexes distribution maps were drawn. Based on the 2009-2018 wind disaster data of facility agriculture and the wind disaster cases of representative provinces in each region in 2020, the wind disaster indexes determined in this study are in good agreement with the disaster-bearing body"s degree of damage and the actual observed wind speed. And the method for determining the wind disaster index was feasible.
Scientific and reasonable disaster indexes are the basis and key to the effective disaster early warning and accurate disaster impact assessment. In this study, based on the disaster-causing principle of wind, the wind disaster indexes of facility agriculture were divided into two levels. The level Ⅰ was for damage to the main structure of the facility, level II was for damage to the shed film. Based on the local climate characteristics and design service life of solar greenhouses and plastic tunnels, the extreme value probability distribution model was used to analyze the maximum wind speed observation data of 2467 weather stations from 1989 to 2018, and the maximum wind speed of 20a and 10a return period were calculated. On this basis, the wind resistance of different types of facilities and the disaster-causing factors were considered, and the wind disaster indexes for solar greenhouses and plastic tunnels of different levels based on extreme wind speed were established. According to the main distribution areas of solar greenhouses and plastic tunnels in China, the wind disaster indexes distribution maps were drawn. Based on the 2009-2018 wind disaster data of facility agriculture and the wind disaster cases of representative provinces in each region in 2020, the wind disaster indexes determined in this study are in good agreement with the disaster-bearing body"s degree of damage and the actual observed wind speed. And the method for determining the wind disaster index was feasible.
Available online: June 02, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.051701
Abstract:
The ratio of transpiration to evapotranspiration (T/ET) is a key parameter to illustrate the role of vegetation in controlling water loss in terrestrial systems. Quantifying evapotranspiration (ET) and its components is a key to understanding the dynamics and mechanism of evapotranspiration and it is the basis for studying the eco-hydrological process. This paper reviewed the research progress of T/ET quantification methods (measurement methods and model methods), T/ET results in different ecosystems and their driving mechanisms (climate change and vegetation cover). The methods were introduced in T/ET observation and simulation developed at home and aboard, and the results of different methods were compared. The values of T/ET were described in four types of terrestrial ecosystems, including forest, grassland, wetland and farmland. There were significant differences in T/ET in the same or even in the different ecosystems, which were mainly due to the differences in ecosystem types, spatial and temporal scales, data sources and quantitative methods, the selection of data set, observation or simulation methods. The main driving mechanisms of T/ET included vegetation type, vegetation cover, climate factors and soil factors. In the future, uncertainty studies around different quantification methods of T/ET, changing patterns and driving mechanisms of T/ET in different terrestrial ecosystems will be emphasized.
The ratio of transpiration to evapotranspiration (T/ET) is a key parameter to illustrate the role of vegetation in controlling water loss in terrestrial systems. Quantifying evapotranspiration (ET) and its components is a key to understanding the dynamics and mechanism of evapotranspiration and it is the basis for studying the eco-hydrological process. This paper reviewed the research progress of T/ET quantification methods (measurement methods and model methods), T/ET results in different ecosystems and their driving mechanisms (climate change and vegetation cover). The methods were introduced in T/ET observation and simulation developed at home and aboard, and the results of different methods were compared. The values of T/ET were described in four types of terrestrial ecosystems, including forest, grassland, wetland and farmland. There were significant differences in T/ET in the same or even in the different ecosystems, which were mainly due to the differences in ecosystem types, spatial and temporal scales, data sources and quantitative methods, the selection of data set, observation or simulation methods. The main driving mechanisms of T/ET included vegetation type, vegetation cover, climate factors and soil factors. In the future, uncertainty studies around different quantification methods of T/ET, changing patterns and driving mechanisms of T/ET in different terrestrial ecosystems will be emphasized.
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032601
Abstract:
The return sounding observation is a new high-altitude observation technique developed in China. In addition to the observation of vertical profile in the ascending stage, at the same time, the atmospheric sounding in the period of floating and falling is added, and the space-time densification of the sounding profile is realized automatically. In this paper, the ERA5 reanalysis data is used as the "true value" , and the return sounding simulation system is used to construct the return sounding simulation observation, an observation System Simulation experiment (OSSEs) was conducted based on GRAPES-MESO and 3D-var assimilation System. The results of numerical experiments show that compared with the traditional single-rise sounding observation, the simulated sounding observation of the descending section of the return sounding can effectively improve the precipitation forecasting skills of GRAPES under the condition of national network formation, at the same time, the forecast of factor field (temperature, humidity and wind field) is improved, the improvement rate is about 2% ~ 5% . In addition, the analysis results of typical weather cases show that the increase of round-trip drift sounding observations can improve the initial model deviation, thus more accurate simulation of precipitation distribution. The research results of this paper provide theoretical support for the future scientific layout and application of the return sounding..
The return sounding observation is a new high-altitude observation technique developed in China. In addition to the observation of vertical profile in the ascending stage, at the same time, the atmospheric sounding in the period of floating and falling is added, and the space-time densification of the sounding profile is realized automatically. In this paper, the ERA5 reanalysis data is used as the "true value" , and the return sounding simulation system is used to construct the return sounding simulation observation, an observation System Simulation experiment (OSSEs) was conducted based on GRAPES-MESO and 3D-var assimilation System. The results of numerical experiments show that compared with the traditional single-rise sounding observation, the simulated sounding observation of the descending section of the return sounding can effectively improve the precipitation forecasting skills of GRAPES under the condition of national network formation, at the same time, the forecast of factor field (temperature, humidity and wind field) is improved, the improvement rate is about 2% ~ 5% . In addition, the analysis results of typical weather cases show that the increase of round-trip drift sounding observations can improve the initial model deviation, thus more accurate simulation of precipitation distribution. The research results of this paper provide theoretical support for the future scientific layout and application of the return sounding..
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050601
Abstract:
This article uses the ground-based vertical remote sensing equipment constructed by the Beijing National Comprehensive Meteorological Observation and Test Base for the super-large city observation test, and the observation data of radiosonde, laser aerosol radar, microwave radiometer and wind profiler radar from May 2021 to August 2021 , according to different The detection advantages of the equipment and the diurnal variation of the boundary layer are combined with the observation data of laser aerosol radar, microwave radiometer, and wind profiler radar to obtain the all-weather atmospheric boundary layer height. Comparing the height of the boundary layer obtained from the inversion with the height of the all-weather atmospheric boundary layer provided by the sounding data calculation and the ERA5 reanalysis data, it is found that: (1) The joint inversion boundary layer height is in good agreement with the atmospheric boundary layer height provided by the ERA5 data. (2) Laser aerosol radar is suitable for the observation of the convective boundary layer during the day, and the microwave radiometer is suitable for the observation of the stable boundary layer at night. The use of microwave radiometer and wind profiler radar to jointly retrieve the height of the atmospheric boundary layer can improve the performance of a single device during rainfall; (3) The joint inversion of the atmospheric boundary layer height result and the single device inversion of the atmospheric boundary layer height are in line with the diurnal variation of the atmospheric boundary layer; (4) The joint inversion of boundary layer height obtained in this article is compared with the height difference of the atmospheric boundary layer obtained from the sounding data. The standard deviation is 51m. Compared with the average value of the atmospheric boundary layer height in a certain range provided by the ERA5 data, joint inversion of the boundary layer height can more accurately reflect the atmospheric boundary layer height in a smaller range.
This article uses the ground-based vertical remote sensing equipment constructed by the Beijing National Comprehensive Meteorological Observation and Test Base for the super-large city observation test, and the observation data of radiosonde, laser aerosol radar, microwave radiometer and wind profiler radar from May 2021 to August 2021 , according to different The detection advantages of the equipment and the diurnal variation of the boundary layer are combined with the observation data of laser aerosol radar, microwave radiometer, and wind profiler radar to obtain the all-weather atmospheric boundary layer height. Comparing the height of the boundary layer obtained from the inversion with the height of the all-weather atmospheric boundary layer provided by the sounding data calculation and the ERA5 reanalysis data, it is found that: (1) The joint inversion boundary layer height is in good agreement with the atmospheric boundary layer height provided by the ERA5 data. (2) Laser aerosol radar is suitable for the observation of the convective boundary layer during the day, and the microwave radiometer is suitable for the observation of the stable boundary layer at night. The use of microwave radiometer and wind profiler radar to jointly retrieve the height of the atmospheric boundary layer can improve the performance of a single device during rainfall; (3) The joint inversion of the atmospheric boundary layer height result and the single device inversion of the atmospheric boundary layer height are in line with the diurnal variation of the atmospheric boundary layer; (4) The joint inversion of boundary layer height obtained in this article is compared with the height difference of the atmospheric boundary layer obtained from the sounding data. The standard deviation is 51m. Compared with the average value of the atmospheric boundary layer height in a certain range provided by the ERA5 data, joint inversion of the boundary layer height can more accurately reflect the atmospheric boundary layer height in a smaller range.
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.051201
Abstract:
The horizontal diffusion term is often used in the model to suppress nonlinear calculation instability or damping of false short waves, but this will cause excessive dissipation of small-scale kinetic energy in the numerical model near the truncation scale, therefore causing prediction uncertainty. In order to compensate the excessively dissipated small-scale kinetic energy back to the model, a Stochastic Kinetic Energy Backscatter (SKEB) method is introduced into the CMA regional ensemble prediction system. First, based on the first-order autoregressive random process in the horizontal direction to expand the spherical harmonic function to obtain the random field, and then construct the random flow function forcing, transform it into horizontal wind speed disturbance, and make random compensation for the dissipated kinetic energy. We carry out a 10-day ensemble prediction test and a randomized time and space scale sensitivity test in September and October 2018 (choose 1st, 7th, 13th, 19th, and 25th), and evaluate the test results. The main conclusions of the research work are as follows: By comparing the ensemble prediction results of the test using the SKEB scheme and the test without the SKEB scheme, the use of the SKEB scheme increases the large aerodynamic energy of the CMA-REPS regional model in the small and medium-scale region, and improves the CMA-REPS ensemble prediction system to the actual atmosphere to some extent. The simulation ability of kinetic energy spectrum; the introduction of SKEB scheme in regional ensemble prediction can significantly improve the spread of U and V in horizontal wind field of regional model. The SKEB program has improved the forecasting skills to a certain extent, such as reducing the CRPS scores of the horizontal wind fields U and V, reducing the outliers scores of the horizontal wind field, temperature, and 10 m wind speed; the introduction of the SKEB method can improve the light rain. The precipitation probability prediction skill score, but the improvement of the score did not pass the significance test, so it is considered that the SKEB method is difficult to improve the probability prediction technique of precipitation. Sensitivity tests based on the SKEB method for six time scales of random pattern (1h, 3h, 6h, 9h,12h, 15h of the time series τ) and five spatial correlation scale (the maximum cutoff wave number Lmax is selected as 80, 100, 120, 160, 200, 240) show that the ensemble prediction is sensitive to the six time scales of the stochastic model of the SKEB method. And the experiment whose time is set to 12h and the maximum truncation wave number is set to 240 show the best performance than the others. Therefore, we can draw the conclusion that the SKEB scheme can compensate for the small-scale kinetic energy dissipated at the truncated scale, and effectively improving forecasting skills.
The horizontal diffusion term is often used in the model to suppress nonlinear calculation instability or damping of false short waves, but this will cause excessive dissipation of small-scale kinetic energy in the numerical model near the truncation scale, therefore causing prediction uncertainty. In order to compensate the excessively dissipated small-scale kinetic energy back to the model, a Stochastic Kinetic Energy Backscatter (SKEB) method is introduced into the CMA regional ensemble prediction system. First, based on the first-order autoregressive random process in the horizontal direction to expand the spherical harmonic function to obtain the random field, and then construct the random flow function forcing, transform it into horizontal wind speed disturbance, and make random compensation for the dissipated kinetic energy. We carry out a 10-day ensemble prediction test and a randomized time and space scale sensitivity test in September and October 2018 (choose 1st, 7th, 13th, 19th, and 25th), and evaluate the test results. The main conclusions of the research work are as follows: By comparing the ensemble prediction results of the test using the SKEB scheme and the test without the SKEB scheme, the use of the SKEB scheme increases the large aerodynamic energy of the CMA-REPS regional model in the small and medium-scale region, and improves the CMA-REPS ensemble prediction system to the actual atmosphere to some extent. The simulation ability of kinetic energy spectrum; the introduction of SKEB scheme in regional ensemble prediction can significantly improve the spread of U and V in horizontal wind field of regional model. The SKEB program has improved the forecasting skills to a certain extent, such as reducing the CRPS scores of the horizontal wind fields U and V, reducing the outliers scores of the horizontal wind field, temperature, and 10 m wind speed; the introduction of the SKEB method can improve the light rain. The precipitation probability prediction skill score, but the improvement of the score did not pass the significance test, so it is considered that the SKEB method is difficult to improve the probability prediction technique of precipitation. Sensitivity tests based on the SKEB method for six time scales of random pattern (1h, 3h, 6h, 9h,12h, 15h of the time series τ) and five spatial correlation scale (the maximum cutoff wave number Lmax is selected as 80, 100, 120, 160, 200, 240) show that the ensemble prediction is sensitive to the six time scales of the stochastic model of the SKEB method. And the experiment whose time is set to 12h and the maximum truncation wave number is set to 240 show the best performance than the others. Therefore, we can draw the conclusion that the SKEB scheme can compensate for the small-scale kinetic energy dissipated at the truncated scale, and effectively improving forecasting skills.
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041001
Abstract:
Using the 10-min surface rainfall observations in Anhui province during the 2011-2018 warm seasons (May to August), the tempo-spatial distributions of Hourly Heavy Rainfall (HHR) events during the pre-Meiyu, Meiyu, and post-Meiyu periods are comparatively analyzed. The results show that the HHR events frequently occur over the areas from Dabie Mountains (Mt.DB) to the southwest of the southern Anhui Mountains (Mt.WN). The contribution of the HHR events over the southwest and northeast of Anhui Province to the total precipitation during the warm-season reaches 30-40%. During the pre-Meiyu period, the HHR events have a lower occurrence frequency and weaker rainfall intensity than the Meiyu and post-Meiyu periods. The HHR events during the Meiyu period last longer and produce a larger rainfall accumulation than those during the pre- and post-Meiyu periods, while those during the post-Meiyu period have larger intensity but shorter duration. Defined using the 99th percentile threshold, more than 60% of the extreme persistent (cumulative rainfall) HHR events take place during the Meiyu period, while more than 60% of the extreme rainfall intensity HHR events occur during the post-Meiyu period. The HHR events’ occurrence frequency peaks at 6:00 and 17:00 during the Meiyu period, while exhibits a prominent single peak at 16:00 during the post-Meiyu period. Using the rotating T model of the principal component analysis, the main synoptic circulation patterns of the HHR events can be classified as the southwest vortex/shear type or front type (SP2) and northwest trough type (SP1) during the Meiyu period. The SP2 type HHR events are the major contributor to the HHR accumulation and mainly occur in Mt. DB, Mt. WN and their transition zones. HHR events of the SP1 type tend to occur in mountainous areas such as Mt.DB, Mt.WN and northeastern Anhui. During the post-Meiyu period, the two major patterns are the southern low-pressure or typhoon type (SP6) and northwest low trough type (SP1). The major contributor to the HHR accumulation is the SP6 type HHR events that occur mainly in Mt. DB and Mt. WN, while the SP1 type HHR events take place more in the north than in the south.
Using the 10-min surface rainfall observations in Anhui province during the 2011-2018 warm seasons (May to August), the tempo-spatial distributions of Hourly Heavy Rainfall (HHR) events during the pre-Meiyu, Meiyu, and post-Meiyu periods are comparatively analyzed. The results show that the HHR events frequently occur over the areas from Dabie Mountains (Mt.DB) to the southwest of the southern Anhui Mountains (Mt.WN). The contribution of the HHR events over the southwest and northeast of Anhui Province to the total precipitation during the warm-season reaches 30-40%. During the pre-Meiyu period, the HHR events have a lower occurrence frequency and weaker rainfall intensity than the Meiyu and post-Meiyu periods. The HHR events during the Meiyu period last longer and produce a larger rainfall accumulation than those during the pre- and post-Meiyu periods, while those during the post-Meiyu period have larger intensity but shorter duration. Defined using the 99th percentile threshold, more than 60% of the extreme persistent (cumulative rainfall) HHR events take place during the Meiyu period, while more than 60% of the extreme rainfall intensity HHR events occur during the post-Meiyu period. The HHR events’ occurrence frequency peaks at 6:00 and 17:00 during the Meiyu period, while exhibits a prominent single peak at 16:00 during the post-Meiyu period. Using the rotating T model of the principal component analysis, the main synoptic circulation patterns of the HHR events can be classified as the southwest vortex/shear type or front type (SP2) and northwest trough type (SP1) during the Meiyu period. The SP2 type HHR events are the major contributor to the HHR accumulation and mainly occur in Mt. DB, Mt. WN and their transition zones. HHR events of the SP1 type tend to occur in mountainous areas such as Mt.DB, Mt.WN and northeastern Anhui. During the post-Meiyu period, the two major patterns are the southern low-pressure or typhoon type (SP6) and northwest low trough type (SP1). The major contributor to the HHR accumulation is the SP6 type HHR events that occur mainly in Mt. DB and Mt. WN, while the SP1 type HHR events take place more in the north than in the south.
Liu Couhua, Dai Kan, Lin Jian, Wei Qing, Li Nina, Wang Baoli, Tang Buxing, Guo Yunqian, Zhu Wenjian, Tang Jian, Zeng Xiaoqing
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050902
Abstract:
In order to evaluate the contribution of each process from numerical forecast, objective method to subjective forecast products to the accuracy of weather forecast, the Meteorological Evaluation Program Library (MetEva) is developed. Aiming at the whole process coverage of the verification algorithm and the comparability of the evaluation results, MetEva adopts a hierarchical architecture including basic layer and functional layer, and designs a modular inspection and calculation process based on a unified data structure. The program library provides over 400 functions around the steps of data reading, data merging and matching, sample selection, sample grouping, inspection calculation and result output for verification. MetEva provides 54 evaluation methods in five categories, which covers most of methods recommended by the World Meteorological Organization and algorithms in domestic specifications. By using matrix calculation in each module and providing parallel scheme for verification algorithms, the operation efficiency is improved. Taking the evaluation of temperature and precipitation forecast as an example, this paper briefly explains the application MetEva, and shows the value of it in verification. The program library has been released as open source, which can effectively support meteorological departments at all levels to carry out the evaluation of the whole process of weather forecast, so as to promote the development of weather forecast.
In order to evaluate the contribution of each process from numerical forecast, objective method to subjective forecast products to the accuracy of weather forecast, the Meteorological Evaluation Program Library (MetEva) is developed. Aiming at the whole process coverage of the verification algorithm and the comparability of the evaluation results, MetEva adopts a hierarchical architecture including basic layer and functional layer, and designs a modular inspection and calculation process based on a unified data structure. The program library provides over 400 functions around the steps of data reading, data merging and matching, sample selection, sample grouping, inspection calculation and result output for verification. MetEva provides 54 evaluation methods in five categories, which covers most of methods recommended by the World Meteorological Organization and algorithms in domestic specifications. By using matrix calculation in each module and providing parallel scheme for verification algorithms, the operation efficiency is improved. Taking the evaluation of temperature and precipitation forecast as an example, this paper briefly explains the application MetEva, and shows the value of it in verification. The program library has been released as open source, which can effectively support meteorological departments at all levels to carry out the evaluation of the whole process of weather forecast, so as to promote the development of weather forecast.
Available online: June 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.052801
Abstract:
By using conventional observation data, automatic meteorological station data and NCEP reanalysis data, with the data of CINRAD and meteorological satellite, the mesoscale weather system development models in the boundary layer of extreme rainstorm under three different weather types are summarized, based on the systematic analysis about the dynamic and thermal characteristics of the boundary layer mesoscale weather system in 39 cases of extreme Rainstorms. The results show that the development of mesoscale weather system in extreme rainstorm has the same regularity under the same weather system. The occurrence of extreme rainstorm is closely related to the strong development of mesoscale weather system in boundary layer. The special topography in the middle reaches of the Yangtze River plays an important role in the occurrence and development of mesoscale weather systems. Under the background of favorable circulation, by the trigger and organization of strong developing mesoscale weather system in boundary layer, the consolidation strengthening, stagnation, backward propagation of MCS and convective cell train effect are important reasons for extreme heavy rainfall. To be specific: (1) There are three paterns of surface mesoscale synoptic systems related to frontal cyclone type, which are all developed from the intersection of cold shear line, warm mesoscale convergence line and the gust front of MCS in the west of Dabie Mountain. (2) Under the background of low vortex shear type, mesoscale weather system is mainly a local mesoscale vortex, newly born in Jianghan Dongting Lake Plain in the eastern Wuling mountains of Hunan and Hubei in boundary layer and the scale is about 150-300km. Its formation is accompanied by the strong convergence of multiple flows in the boundary layer and the development of local baroclinicity. The strengthening of the southwest vortex and the formation of heavy precipitation in front of the second-order regional vortex in the west of Hunan and Hubei are the main inducements for the development of local mesoscale vortex in the boundary layer of the eastern plain. The horseshoe shaped terrain in the middle reaches of the Yangtze River, which is conducive to the convergence of multiple air streams, is the key factor for the occurrence of local mesoscale vortex in the eastern plain. (3)The formation and development of the extreme rainstorm mesoscale weather system in the warm sector of the weakly forced Meiyu front is mainly related to the enhanced convergence and maintenance of the thunderstorm cold pool countercurrent on the westside of the Dabie Mountains and the nighttime boundary layer ultra-low-level jet.
By using conventional observation data, automatic meteorological station data and NCEP reanalysis data, with the data of CINRAD and meteorological satellite, the mesoscale weather system development models in the boundary layer of extreme rainstorm under three different weather types are summarized, based on the systematic analysis about the dynamic and thermal characteristics of the boundary layer mesoscale weather system in 39 cases of extreme Rainstorms. The results show that the development of mesoscale weather system in extreme rainstorm has the same regularity under the same weather system. The occurrence of extreme rainstorm is closely related to the strong development of mesoscale weather system in boundary layer. The special topography in the middle reaches of the Yangtze River plays an important role in the occurrence and development of mesoscale weather systems. Under the background of favorable circulation, by the trigger and organization of strong developing mesoscale weather system in boundary layer, the consolidation strengthening, stagnation, backward propagation of MCS and convective cell train effect are important reasons for extreme heavy rainfall. To be specific: (1) There are three paterns of surface mesoscale synoptic systems related to frontal cyclone type, which are all developed from the intersection of cold shear line, warm mesoscale convergence line and the gust front of MCS in the west of Dabie Mountain. (2) Under the background of low vortex shear type, mesoscale weather system is mainly a local mesoscale vortex, newly born in Jianghan Dongting Lake Plain in the eastern Wuling mountains of Hunan and Hubei in boundary layer and the scale is about 150-300km. Its formation is accompanied by the strong convergence of multiple flows in the boundary layer and the development of local baroclinicity. The strengthening of the southwest vortex and the formation of heavy precipitation in front of the second-order regional vortex in the west of Hunan and Hubei are the main inducements for the development of local mesoscale vortex in the boundary layer of the eastern plain. The horseshoe shaped terrain in the middle reaches of the Yangtze River, which is conducive to the convergence of multiple air streams, is the key factor for the occurrence of local mesoscale vortex in the eastern plain. (3)The formation and development of the extreme rainstorm mesoscale weather system in the warm sector of the weakly forced Meiyu front is mainly related to the enhanced convergence and maintenance of the thunderstorm cold pool countercurrent on the westside of the Dabie Mountains and the nighttime boundary layer ultra-low-level jet.
Available online: May 30, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.040901
Abstract:
On July 30, 2015, extreme heavy precipitation broke out in a wide range of warm areas in Shandong, the prediction deviation was large because the triggering mechanism was not obvious and the judgment of the development direction of the convection system was insufficient. By using multi-source observational data, the triggering and evolution of convective system organization were analyzed in this paper. The results show that the upper trough and the low-level jet favor the occurrence and development of the deep wet convection. There are sufficient water vapor and favorable thermal condition before the convection. The horizontal convective rolls showed on the cloud and radar maps indicate that the potential of convection generation and development is enhanced. The cold air intrudes into northern Shandong through Bohai Sea and triggers the original convection, which further strengthens to generate the surface cold pool and the gust front. The gust front continues to trigger convection, forming a backward developing multi-cell storm. At this stage, the low-level environmental wind direction determines the development direction of convective storms. The mechanism for the organization and maintenance of the convective system is as follows: the strengthening of the surface cold pool and the development of convective storms form a positive feedback, the surface cold pool and low-level environmental vertical wind shear reach a dynamic balance, and the multi-cell storm gradually develops into a linear mesoscale convective system(LMCS). With the gradual enhancement of the deep vertical wind shear, the structure of LMCS becomes closer.The mechanism of weakening and extinction of convective system is as follows: blocked by the terrain in the middle mountain area of Shandong Province, the main body of the surface cold pool remains in the middle of Shandong Province, the intensity of the gust front in the front of the cold pool decreases rapidly, and the LMCS is divided into East and West segments, then the East and West segments of the LMCS weakens and dies under the unfavorable low-level vertical wind shear. The RKW theory is applicable to explain the evolution of the LMCS organization.
On July 30, 2015, extreme heavy precipitation broke out in a wide range of warm areas in Shandong, the prediction deviation was large because the triggering mechanism was not obvious and the judgment of the development direction of the convection system was insufficient. By using multi-source observational data, the triggering and evolution of convective system organization were analyzed in this paper. The results show that the upper trough and the low-level jet favor the occurrence and development of the deep wet convection. There are sufficient water vapor and favorable thermal condition before the convection. The horizontal convective rolls showed on the cloud and radar maps indicate that the potential of convection generation and development is enhanced. The cold air intrudes into northern Shandong through Bohai Sea and triggers the original convection, which further strengthens to generate the surface cold pool and the gust front. The gust front continues to trigger convection, forming a backward developing multi-cell storm. At this stage, the low-level environmental wind direction determines the development direction of convective storms. The mechanism for the organization and maintenance of the convective system is as follows: the strengthening of the surface cold pool and the development of convective storms form a positive feedback, the surface cold pool and low-level environmental vertical wind shear reach a dynamic balance, and the multi-cell storm gradually develops into a linear mesoscale convective system(LMCS). With the gradual enhancement of the deep vertical wind shear, the structure of LMCS becomes closer.The mechanism of weakening and extinction of convective system is as follows: blocked by the terrain in the middle mountain area of Shandong Province, the main body of the surface cold pool remains in the middle of Shandong Province, the intensity of the gust front in the front of the cold pool decreases rapidly, and the LMCS is divided into East and West segments, then the East and West segments of the LMCS weakens and dies under the unfavorable low-level vertical wind shear. The RKW theory is applicable to explain the evolution of the LMCS organization.
Available online: May 24, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.040203
Abstract:
Based on the prediction equation of air pollution concentration, the meteorological factors which affected on the air pollution were constructed and daily increment of air quality index (AQI) was as the object to quantitatively classify the air pollution potential. The atmospheric circulation background was divided into cold, mixed and warm air circulations in autumn and winter by the Q-type cluster analysis method, which was built on synoptic theory. The meteorological factor and its thresholds for distinguishing three types of atmospheric circulation were studied. Used the Bayes discriminant analysis method, the five grads prediction models of pollution potential were established which the discriminant accuracy were 80%, 71% and 74.7% for cold, mixed and warm air circulations respectively, by the predictive classification model in data mining technology. The mean accuracy of three air types reached 75.2%, which can reach 63.6% when the five grads prediction models were tested by external data validation method. Through comparison of atmospheric self-purification index (ASI) and model discriminant results with daily increment of AQI in autumn and winter from 2019 to 2021, the results shows the model discriminant results was more consistent with the daily increment of AQI in the trend than ASI, and the correlation coefficient was above 0.67. The correct number of grad discrimination by prediction models in extremely favorable and extremely unfavorable pollutant diffusion was significantly higher than by AQI.
Based on the prediction equation of air pollution concentration, the meteorological factors which affected on the air pollution were constructed and daily increment of air quality index (AQI) was as the object to quantitatively classify the air pollution potential. The atmospheric circulation background was divided into cold, mixed and warm air circulations in autumn and winter by the Q-type cluster analysis method, which was built on synoptic theory. The meteorological factor and its thresholds for distinguishing three types of atmospheric circulation were studied. Used the Bayes discriminant analysis method, the five grads prediction models of pollution potential were established which the discriminant accuracy were 80%, 71% and 74.7% for cold, mixed and warm air circulations respectively, by the predictive classification model in data mining technology. The mean accuracy of three air types reached 75.2%, which can reach 63.6% when the five grads prediction models were tested by external data validation method. Through comparison of atmospheric self-purification index (ASI) and model discriminant results with daily increment of AQI in autumn and winter from 2019 to 2021, the results shows the model discriminant results was more consistent with the daily increment of AQI in the trend than ASI, and the correlation coefficient was above 0.67. The correct number of grad discrimination by prediction models in extremely favorable and extremely unfavorable pollutant diffusion was significantly higher than by AQI.
Available online: May 20, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041801
Abstract:
The thunderstorm gale event from 10 to 13 grade overturned a fishing ship along the Shandong Coast on 29 April 2021. The causes of this thunderstorm gale process were investigated based on Doppler weather radar, encryption automatic weather station, ERA5 reanalysis and the conventional observation data. The results show that: (1) The cold and dry air coming from northwest behind the northeast China cold vortex superimposed on the lower-level warm ridge, the strong potential instability stratification and vertical wind shear provided favorable environmental conditions for this severe convection weather. (2) Under the influence of the strong upper-level northwest steering currents, on the one hand, the advection of both the Qingdao storm and the gust front were fast, and on the other hand, the angular momentum of downdraft was increased due to momentum downward-transporting. The gust front lasted for a long time and moved fast, causing thunderstorm gale from 10 to 13 grads through it passed. (3) Dry air in the middle-low troposphere and evaporative cooling of upper-level hydrometeor during its falling process, which forming a cold pool with thickness up to 120hPa near the ground. Allobaric wind formed between the pressurization area at the rear of the large-scale cyclone superimposed with the small-scale cold pool and the decompression area of the cyclone. Density currents between the cold pool and warm ridge at Rizhao superimposed with allobaric wind lead to enhancement of surface wind. (4) Considering the orientation of the pressure gradient had changed after the high pressure cold-core entering sea. Wind direction rotated so that the risk of fishing boat overturning increased. (5) The evaporation, gradient of the frontal zone, intensity of density flow and superposition effect of the multi-scale weather system over Rizhao, were all stronger than those in Qingdao. Results showed that the thunderstorm gales above 10 grade in Rizhao City, which was on the edge of Qingdao thunderstorm, had a greater intensity and scope than those in Qingdao City, which was affected by the main body.
The thunderstorm gale event from 10 to 13 grade overturned a fishing ship along the Shandong Coast on 29 April 2021. The causes of this thunderstorm gale process were investigated based on Doppler weather radar, encryption automatic weather station, ERA5 reanalysis and the conventional observation data. The results show that: (1) The cold and dry air coming from northwest behind the northeast China cold vortex superimposed on the lower-level warm ridge, the strong potential instability stratification and vertical wind shear provided favorable environmental conditions for this severe convection weather. (2) Under the influence of the strong upper-level northwest steering currents, on the one hand, the advection of both the Qingdao storm and the gust front were fast, and on the other hand, the angular momentum of downdraft was increased due to momentum downward-transporting. The gust front lasted for a long time and moved fast, causing thunderstorm gale from 10 to 13 grads through it passed. (3) Dry air in the middle-low troposphere and evaporative cooling of upper-level hydrometeor during its falling process, which forming a cold pool with thickness up to 120hPa near the ground. Allobaric wind formed between the pressurization area at the rear of the large-scale cyclone superimposed with the small-scale cold pool and the decompression area of the cyclone. Density currents between the cold pool and warm ridge at Rizhao superimposed with allobaric wind lead to enhancement of surface wind. (4) Considering the orientation of the pressure gradient had changed after the high pressure cold-core entering sea. Wind direction rotated so that the risk of fishing boat overturning increased. (5) The evaporation, gradient of the frontal zone, intensity of density flow and superposition effect of the multi-scale weather system over Rizhao, were all stronger than those in Qingdao. Results showed that the thunderstorm gales above 10 grade in Rizhao City, which was on the edge of Qingdao thunderstorm, had a greater intensity and scope than those in Qingdao City, which was affected by the main body.
Available online: May 19, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032802
Abstract:
By using meteorological ground and high resolution observation data, automatic station data, satellite imagery and ERA5 data,the temporal and spatial distribution characteristics of summer fog in Beijing- Tianjin- Hebei region from 2000 to 2019 were analyzed．The synoptic weather patterns of summer fog was established, and the typical cases were analyzed. The results show that there were 1 to 4 days of summer fog every year in most of the Beijing –Tianjin-Hebei region．Minimum visibility was relatively low with fog in the northwest, northeast and southeast．Average minimum visibility from central Zhangjiakou to northwest Baoding, southeast Baoding to central Cangzhou and Hengshui areas could be as low as 300 m． The spatial difference of duration of summer fog in plain area was small, generally 1 to 1．4 days, and the duration in mountainous area was relatively long． The generation and dissipation of fog had obvious diurnal changes, the morning before and after sunrise high, after sunrise dissipate within 3 hours． In summer, when the fog appeared, the bottom of the inversion layer was usually high, the thickness was thin, the temperature difference was small and the intensity was weak． The daily temperature range on the ground was above 7℃, and the wind speed was 1 to 2．4 m?s-1, which was an important condition for the formation of fog． The wind direction was mainly southerly or northerly when fog occured．Three typical synoptic weather patterns of summer fog in Beijing-Tianjin-Hebei region were radiation fog under the control of high pressure ridge, advection radiation fog under the control of southwest airflow in front of upper trough, rain fog under the control of subtropical high pressure．
By using meteorological ground and high resolution observation data, automatic station data, satellite imagery and ERA5 data,the temporal and spatial distribution characteristics of summer fog in Beijing- Tianjin- Hebei region from 2000 to 2019 were analyzed．The synoptic weather patterns of summer fog was established, and the typical cases were analyzed. The results show that there were 1 to 4 days of summer fog every year in most of the Beijing –Tianjin-Hebei region．Minimum visibility was relatively low with fog in the northwest, northeast and southeast．Average minimum visibility from central Zhangjiakou to northwest Baoding, southeast Baoding to central Cangzhou and Hengshui areas could be as low as 300 m． The spatial difference of duration of summer fog in plain area was small, generally 1 to 1．4 days, and the duration in mountainous area was relatively long． The generation and dissipation of fog had obvious diurnal changes, the morning before and after sunrise high, after sunrise dissipate within 3 hours． In summer, when the fog appeared, the bottom of the inversion layer was usually high, the thickness was thin, the temperature difference was small and the intensity was weak． The daily temperature range on the ground was above 7℃, and the wind speed was 1 to 2．4 m?s-1, which was an important condition for the formation of fog． The wind direction was mainly southerly or northerly when fog occured．Three typical synoptic weather patterns of summer fog in Beijing-Tianjin-Hebei region were radiation fog under the control of high pressure ridge, advection radiation fog under the control of southwest airflow in front of upper trough, rain fog under the control of subtropical high pressure．
Available online: May 19, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050901
Abstract:
Based on the observationof Parsivel disdrometer at Shangqiu station in Henan Province, Feicheng and Shuguang station in Shandong Province, Lushun and Changhai station in Liaoning Province, theraindrop size distribution of typhoon ‘Rumbia’after landfall in 2018 are analyzed. The results show that: Shangqiu, Feicheng and Shouguang has the similar Characteristics of the average raindrop size distributionat different rain intensiitieswith high concentration of small raindrops and low concentration of large raindrops, and part of the average drop size distributions have the characteristics of balanced raindrop size distributions. On the contrary, the average raindrop size distributions in Lushun and Changhai have low concentration of small raindrop and high concentration of large raindrop, and the average raindrop size distribution is controlled by ice phase.TheZ-R relationship between Shangqiu, Feicheng and Shouguang is similar, and the Z-R relationship between Lushun and Changhai is similar. There is a great different indexesbetween the two types, indicating that the microphysical characteristics of precipitation are obviously different.The parameter (lgNw-Dm) of normalized Gamma distribution of raindrop size distribution shows that: the convective precipitationsoccurred inS Shangqiu, Feicheng and Shouguang have the characteristics of oceanic raindrop size distribution, and the microphysical processes are mainly warm rain process, which is dominated by clashing and growing, and mixing of warm rain and ice phase. By contrast,Sthe convective precipitations in Lushun and Changhai have the characteristics of continental raindrop size distribution, and the microphysical processes are predominated by ice phaseandmixing of warm rain and ice phase.The above shows that although the typhoon‘Rumbia’ in Henan and Shandong were affected by cold air continuously, there is no obvious change in the microphysical characteristics, the cloud microphysical process changed significantly after it weakened into an extratropical cyclone.
Based on the observationof Parsivel disdrometer at Shangqiu station in Henan Province, Feicheng and Shuguang station in Shandong Province, Lushun and Changhai station in Liaoning Province, theraindrop size distribution of typhoon ‘Rumbia’after landfall in 2018 are analyzed. The results show that: Shangqiu, Feicheng and Shouguang has the similar Characteristics of the average raindrop size distributionat different rain intensiitieswith high concentration of small raindrops and low concentration of large raindrops, and part of the average drop size distributions have the characteristics of balanced raindrop size distributions. On the contrary, the average raindrop size distributions in Lushun and Changhai have low concentration of small raindrop and high concentration of large raindrop, and the average raindrop size distribution is controlled by ice phase.TheZ-R relationship between Shangqiu, Feicheng and Shouguang is similar, and the Z-R relationship between Lushun and Changhai is similar. There is a great different indexesbetween the two types, indicating that the microphysical characteristics of precipitation are obviously different.The parameter (lgNw-Dm) of normalized Gamma distribution of raindrop size distribution shows that: the convective precipitationsoccurred inS Shangqiu, Feicheng and Shouguang have the characteristics of oceanic raindrop size distribution, and the microphysical processes are mainly warm rain process, which is dominated by clashing and growing, and mixing of warm rain and ice phase. By contrast,Sthe convective precipitations in Lushun and Changhai have the characteristics of continental raindrop size distribution, and the microphysical processes are predominated by ice phaseandmixing of warm rain and ice phase.The above shows that although the typhoon‘Rumbia’ in Henan and Shandong were affected by cold air continuously, there is no obvious change in the microphysical characteristics, the cloud microphysical process changed significantly after it weakened into an extratropical cyclone.
Available online: May 18, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032401
Abstract:
In this paper, focusing on the large-scale weather systems, we analyze the correlations between the atmospheric circulation configuration and the air pollution episodes in Jinan City, and further explore the influence mechanisms of cold air with different intensities on the air pollution episodes. The results show that during 2016–2018 more than 75% of PM 2.5 pollution episodes in Jinan occurred in the surface uniform pressure field. If the equal occurrence probability of each weather pattern was equal, the surface weather pattern with the highest occurrence probability of pollution episodes is the inverted trough pattern (>55%), followed by the uniform pressure field pattern (26.8%). Moreover, there is a more than 25% occurrence probability of PM2.5 pollution when the 500 hPa circulation is controlled by such weather systems, i.e., the ridge, straight westerlies, the anticyclone, behind the trough and in front of the trough. The circulation configuration at upper and lower levels with the greatest probability of PM2.5 pollution (>50%) in Jinan is the type of the surface inverted trough and behind the upper-level trough, followed by the type of the surface inverted trough and the upper-level straight westerlies, and the type of the surface uniform pressure field and behind the upper-level trough. For the average, the mixed layer height is below 1000 m during PM 2.5 pollution episodes and is less than 800 m under heavy pollution. During pollution periods, the average relative humidity is 65%±20%, and the average temperature is 6±1°C. The effect of cold air with different intensities on the pollutant episodes is complex. The stronger cold air (ΔTh24 > 4.3°C, ΔPh24 > 4.74 hPa) with a certain duration, such as the northerly wind greater than 3.5 m?s?1 lasting more than 9.6 hours, can remove pollutants completely. The slightly weaker cold air may be beneficial to reduce pollutant concentration. However, the weak cold air with a lower northerly wind speed may instead increase the pollutant concentration due to the transport of pollutants.
In this paper, focusing on the large-scale weather systems, we analyze the correlations between the atmospheric circulation configuration and the air pollution episodes in Jinan City, and further explore the influence mechanisms of cold air with different intensities on the air pollution episodes. The results show that during 2016–2018 more than 75% of PM 2.5 pollution episodes in Jinan occurred in the surface uniform pressure field. If the equal occurrence probability of each weather pattern was equal, the surface weather pattern with the highest occurrence probability of pollution episodes is the inverted trough pattern (>55%), followed by the uniform pressure field pattern (26.8%). Moreover, there is a more than 25% occurrence probability of PM2.5 pollution when the 500 hPa circulation is controlled by such weather systems, i.e., the ridge, straight westerlies, the anticyclone, behind the trough and in front of the trough. The circulation configuration at upper and lower levels with the greatest probability of PM2.5 pollution (>50%) in Jinan is the type of the surface inverted trough and behind the upper-level trough, followed by the type of the surface inverted trough and the upper-level straight westerlies, and the type of the surface uniform pressure field and behind the upper-level trough. For the average, the mixed layer height is below 1000 m during PM 2.5 pollution episodes and is less than 800 m under heavy pollution. During pollution periods, the average relative humidity is 65%±20%, and the average temperature is 6±1°C. The effect of cold air with different intensities on the pollutant episodes is complex. The stronger cold air (ΔTh24 > 4.3°C, ΔPh24 > 4.74 hPa) with a certain duration, such as the northerly wind greater than 3.5 m?s?1 lasting more than 9.6 hours, can remove pollutants completely. The slightly weaker cold air may be beneficial to reduce pollutant concentration. However, the weak cold air with a lower northerly wind speed may instead increase the pollutant concentration due to the transport of pollutants.
Available online: May 18, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032202
Abstract:
The climate comfort index (CCI) is the basis of the forecast of weather comfort degree and climate resource assessment for health tourism. A lot of bioclimatic index have been developed for wide range of purposes since the earlier years of the last century but there is still lack of a kind of CCI which could be able to accurately describe human comfort perception to different weather conditions in various climate zones of
The climate comfort index (CCI) is the basis of the forecast of weather comfort degree and climate resource assessment for health tourism. A lot of bioclimatic index have been developed for wide range of purposes since the earlier years of the last century but there is still lack of a kind of CCI which could be able to accurately describe human comfort perception to different weather conditions in various climate zones of
Available online: May 16, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.020901
Abstract:
The Dongtan site, located in a national natural reserve on Chongmin island of Shanghai, has been developed to carry out atmospheric composition measurements since 2006. Based on the particulate matter and meteorological measurements from 2008 to 2015 at Dongtan, the arriving air mass is classified, the PM2.5 background level and its annual variation are examined, the potential source of higher level of PM2.5 is also identified in this article. The annual variation of PM2.5 concentration presents in-significant trend from 2008 to 2015, but stable fluctuation from 26.8 to 32.7 μg?m^(-3). However, the ratio of PM2.5/PM10 increases from 0.84 to 0.92, indicating more and more formation of secondary aerosols observed at Dongtan. The air mass arriving at Dongtan could be aggregated into 3 types of back trajectories, named as land, ocean, and land/ocean mixing, accounting for 32%, 37.8% and 29.3% respectively. In which, the PM2.5 background concentration ranges stably from 11~15μg·m-3 in ocean air mass, but 29~56 μg?m^(-3) in land air mass, showing largely seasonal variability. The potential source of relatively higher PM2.5 observed at Dongtan presents clear seasonal transition from areas north to Shanghai including Jingjinji, Huanghuai and Jiangsu, Anhui provinces in autumn and winter to southern YRD region including Zhejiang province and its seaboard extending to Fujian province in summer by PSCF analysis. In general, higher PM2.5 loading at Dongtan is mostly contributed by air mass from Shanghai and its neighboring city clusters including Suzhou, Wuxi, Changzhou, Hangzhou, Jiaxing and Huzhou etc. It is noting that air mass recycled from Yellow sea and Bo sea is also the important source area for the elevated PM2.5 observed at Dongtan in spring, autumn and winter.
The Dongtan site, located in a national natural reserve on Chongmin island of Shanghai, has been developed to carry out atmospheric composition measurements since 2006. Based on the particulate matter and meteorological measurements from 2008 to 2015 at Dongtan, the arriving air mass is classified, the PM2.5 background level and its annual variation are examined, the potential source of higher level of PM2.5 is also identified in this article. The annual variation of PM2.5 concentration presents in-significant trend from 2008 to 2015, but stable fluctuation from 26.8 to 32.7 μg?m^(-3). However, the ratio of PM2.5/PM10 increases from 0.84 to 0.92, indicating more and more formation of secondary aerosols observed at Dongtan. The air mass arriving at Dongtan could be aggregated into 3 types of back trajectories, named as land, ocean, and land/ocean mixing, accounting for 32%, 37.8% and 29.3% respectively. In which, the PM2.5 background concentration ranges stably from 11~15μg·m-3 in ocean air mass, but 29~56 μg?m^(-3) in land air mass, showing largely seasonal variability. The potential source of relatively higher PM2.5 observed at Dongtan presents clear seasonal transition from areas north to Shanghai including Jingjinji, Huanghuai and Jiangsu, Anhui provinces in autumn and winter to southern YRD region including Zhejiang province and its seaboard extending to Fujian province in summer by PSCF analysis. In general, higher PM2.5 loading at Dongtan is mostly contributed by air mass from Shanghai and its neighboring city clusters including Suzhou, Wuxi, Changzhou, Hangzhou, Jiaxing and Huzhou etc. It is noting that air mass recycled from Yellow sea and Bo sea is also the important source area for the elevated PM2.5 observed at Dongtan in spring, autumn and winter.
Available online: May 13, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041301
Abstract:
Based on the surface observation and ERA5 hourly reanalysis data from 2000 to 2014, 43 factors were selected to characterize the temperature, humidity and microphysical characteristics of four types of precipitation phases ( rain, snow, sleet, freezing rain). The objective forecast method of precipitation type in the middle reaches of Yangtze River is studied by using CatBoost algorithm based on SMOTEEN sampling. The results show that this method has good classification and forecast effect for rain, snow and freezing rain. The accuracy and spatial fineness of precipitation type discrimination can be improved by using the fine terrain height pre-processing. Compared with the ECMWF, the prediction accuracy of rain, snow and freezing rain has increased by 9.9%, 39.1% and 11.1% respectively, but the improvement of sleet was not obvious.
Based on the surface observation and ERA5 hourly reanalysis data from 2000 to 2014, 43 factors were selected to characterize the temperature, humidity and microphysical characteristics of four types of precipitation phases ( rain, snow, sleet, freezing rain). The objective forecast method of precipitation type in the middle reaches of Yangtze River is studied by using CatBoost algorithm based on SMOTEEN sampling. The results show that this method has good classification and forecast effect for rain, snow and freezing rain. The accuracy and spatial fineness of precipitation type discrimination can be improved by using the fine terrain height pre-processing. Compared with the ECMWF, the prediction accuracy of rain, snow and freezing rain has increased by 9.9%, 39.1% and 11.1% respectively, but the improvement of sleet was not obvious.
Available online: May 13, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050702
Abstract:
Using the S-band dual-polarization radar data and the surface precipitation phenomenon instrument data, the process of a hailstorm severe convective weather in Yongding District of Longyan on 27 March 2020 was analyzed, and compared with the short-term heavy precipitation characteristics occurred in Zhangping at a similar time. The results show that the echo height of hail cloud in Yongding jumped before hail shooting.There is a bounded weak echo in front of the cloud moving direction, and the ZDR arc with an intensity of 2~4 dB also appears there. The KDP column develops high inner hailstorm simultaneously, up to 7~8 km. The KDP column also appears in the heavy rainfall cloud in Zhangping, but its height is lower. There are hailstones aloft in Zhangping, but heavy rainfalls with large raindrops appear on the ground for hail stones melting during falling. In the front of these two strong convective clouds, the large drop(>3mm) ends increased firstly with raindrop spectrum boarding, showing double or multi-peaks. While the strong center of convective cloud moving closer, the concentration of small rain drops(≤1mm) increases in magnitude. It is related to the separate fall tracks of large and small raindrops caused by the strong environmental vertical wind shear in the front of convective cloud. In the hail shooting or heavy precipitation stage, the hailstones have low density and raindrop spectrums show weak double peaks at Yongding station, while single-peaks present at Zhangping station. The large drops at the two stations in this stage are mostly caused by the melting from small hails. The double-peak structure of the raindrop spectrum after hail shooting is mainly caused by the collision of raindrops. The raindrop spectrums at the tail of the cloud become narrow, with decreasing in magnitude of small particles.
Using the S-band dual-polarization radar data and the surface precipitation phenomenon instrument data, the process of a hailstorm severe convective weather in Yongding District of Longyan on 27 March 2020 was analyzed, and compared with the short-term heavy precipitation characteristics occurred in Zhangping at a similar time. The results show that the echo height of hail cloud in Yongding jumped before hail shooting.There is a bounded weak echo in front of the cloud moving direction, and the ZDR arc with an intensity of 2~4 dB also appears there. The KDP column develops high inner hailstorm simultaneously, up to 7~8 km. The KDP column also appears in the heavy rainfall cloud in Zhangping, but its height is lower. There are hailstones aloft in Zhangping, but heavy rainfalls with large raindrops appear on the ground for hail stones melting during falling. In the front of these two strong convective clouds, the large drop(>3mm) ends increased firstly with raindrop spectrum boarding, showing double or multi-peaks. While the strong center of convective cloud moving closer, the concentration of small rain drops(≤1mm) increases in magnitude. It is related to the separate fall tracks of large and small raindrops caused by the strong environmental vertical wind shear in the front of convective cloud. In the hail shooting or heavy precipitation stage, the hailstones have low density and raindrop spectrums show weak double peaks at Yongding station, while single-peaks present at Zhangping station. The large drops at the two stations in this stage are mostly caused by the melting from small hails. The double-peak structure of the raindrop spectrum after hail shooting is mainly caused by the collision of raindrops. The raindrop spectrums at the tail of the cloud become narrow, with decreasing in magnitude of small particles.
ZHU Shizhen, ZHANG Zhaoyi, WU Shixiao, YANG Jun, WANG Zhaoyu, SHI Chune, HU Hanfeng, ZHANG Hao, NI Ting, QIU Yujun, LU Chunsong
Available online: May 13, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.021001
Abstract:
Using the fog droplet spectrum and visibility data of two dense fog processes on January 12-13, 2019 in Shou County, Anhui Province, the microphysical characteristics (such as the spectral distribution, droplet number concentration, liquid water content, average diameter, spectral width, etc. )and the correlations among microphysical properties(number concentration, liquid water content, average diameter) in the different stages of fog are analyzed. The result shows that: both fog processes are radiation fog. If the strong inversion structure close to the ground maintains, the water vapor will be restrained in the inversion layer. It is conducive to the long-term maintenance of dense fog. The formation time of the fog at 20 m is later than that of the ground. In the early stage of formation, development and maturity, the microphysical characteristics of the ground fog are all larger than that at 20 m. At the late stage of maturity, the release of latent heat by condensation and ground heating may increase the intensity of turbulent mixing in the fog, making the fog uniform in the vertical direction. The fog processes at two heights are dominated by nucleation and condensation growth, but the collision-coalescence process also plays an important role in the fog on the ground. From the stage of formation, development to maturity, the collision-coalescence processes of the ground fog gradually strengthens. The correlation between the number concentration, water content, and average diameter generally ranges from a strong positive correlation to a weak positive or negative correlation. From the early stage to the late stage of the mature stage, the average diameter and number concentration of the fog at 20 m height change from a positive correlation to a negative correlation, which may be related to the factors such as turbulent, entrainment mixing, etc.
Using the fog droplet spectrum and visibility data of two dense fog processes on January 12-13, 2019 in Shou County, Anhui Province, the microphysical characteristics (such as the spectral distribution, droplet number concentration, liquid water content, average diameter, spectral width, etc. )and the correlations among microphysical properties(number concentration, liquid water content, average diameter) in the different stages of fog are analyzed. The result shows that: both fog processes are radiation fog. If the strong inversion structure close to the ground maintains, the water vapor will be restrained in the inversion layer. It is conducive to the long-term maintenance of dense fog. The formation time of the fog at 20 m is later than that of the ground. In the early stage of formation, development and maturity, the microphysical characteristics of the ground fog are all larger than that at 20 m. At the late stage of maturity, the release of latent heat by condensation and ground heating may increase the intensity of turbulent mixing in the fog, making the fog uniform in the vertical direction. The fog processes at two heights are dominated by nucleation and condensation growth, but the collision-coalescence process also plays an important role in the fog on the ground. From the stage of formation, development to maturity, the collision-coalescence processes of the ground fog gradually strengthens. The correlation between the number concentration, water content, and average diameter generally ranges from a strong positive correlation to a weak positive or negative correlation. From the early stage to the late stage of the mature stage, the average diameter and number concentration of the fog at 20 m height change from a positive correlation to a negative correlation, which may be related to the factors such as turbulent, entrainment mixing, etc.
Available online: May 13, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032502
Abstract:
Based on the precipitation forecast data of convection-permitting ensemble prediction system and observation data from April to September in 2017, 2018 and 2019, the effects of 24 h accumulated precipitation forecast of ensemble members in Eastern Sichuan Basin are verified and compared, and the performance of different physics parameterization schemes is further discussed. Results show that: (1) The ensemble average forecast and probability matching forecast have obvious advantages over the ensemble members. (2) The prediction performance of Kain-Fritsch (KF) and Betts-Miller-Janjic (BMJ) cumulus parameterization schemes is relatively good, while the Critical Success Index (CSI) score of Grell 3D ensemble (G3) scheme is relatively low after 48 h. (3) Thompson and Morrison microphysics parameterization schemes are better for light rain than WRF Single-Moment 6-class (WSM6) scheme, while WSM6 scheme is better for moderate rain, and there is no significant difference in the CSI scores of heavy rain and rainstorm among the three schemes. (4) The CSI score of Mellor-Yamada-Janjic (MYJ) and Mellor-Yamada-Nakanishi-Niino (MYNN) boundary layer schemes is higher than that of Yonsei University (YSU) scheme, especially after 48 h. However, YSU scheme is mostly used in combination with G3 scheme, so its low score is mainly affected by G3. (5) The precipitation distribution characteristics of different schemes are similar to those of observation, but the false strong rain belt is predicted in Huaying Mountain, Wuling Mountain and Dalou Mountain, and the precipitation from the middle to the northeast of Chongqing is underestimated. (6) The precipitation forecast in Eastern Sichuan Basin is most sensitive to cumulus parameterization scheme. After adjusting one member"s G3 scheme to KF scheme, not only the forecast score is significantly improved, but also the ensemble spread is increased, and the skill of probability forecast is improved.
Based on the precipitation forecast data of convection-permitting ensemble prediction system and observation data from April to September in 2017, 2018 and 2019, the effects of 24 h accumulated precipitation forecast of ensemble members in Eastern Sichuan Basin are verified and compared, and the performance of different physics parameterization schemes is further discussed. Results show that: (1) The ensemble average forecast and probability matching forecast have obvious advantages over the ensemble members. (2) The prediction performance of Kain-Fritsch (KF) and Betts-Miller-Janjic (BMJ) cumulus parameterization schemes is relatively good, while the Critical Success Index (CSI) score of Grell 3D ensemble (G3) scheme is relatively low after 48 h. (3) Thompson and Morrison microphysics parameterization schemes are better for light rain than WRF Single-Moment 6-class (WSM6) scheme, while WSM6 scheme is better for moderate rain, and there is no significant difference in the CSI scores of heavy rain and rainstorm among the three schemes. (4) The CSI score of Mellor-Yamada-Janjic (MYJ) and Mellor-Yamada-Nakanishi-Niino (MYNN) boundary layer schemes is higher than that of Yonsei University (YSU) scheme, especially after 48 h. However, YSU scheme is mostly used in combination with G3 scheme, so its low score is mainly affected by G3. (5) The precipitation distribution characteristics of different schemes are similar to those of observation, but the false strong rain belt is predicted in Huaying Mountain, Wuling Mountain and Dalou Mountain, and the precipitation from the middle to the northeast of Chongqing is underestimated. (6) The precipitation forecast in Eastern Sichuan Basin is most sensitive to cumulus parameterization scheme. After adjusting one member"s G3 scheme to KF scheme, not only the forecast score is significantly improved, but also the ensemble spread is increased, and the skill of probability forecast is improved.
Available online: May 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.050501
Abstract:
In view of the outstanding problems in the precipitation and model forecasts of the landfalling typhoons in South China, this paper analyzes the current research of the asymmetry of the precipitation distribution of the landfalling typhoon and the mechanism of the continuous rainstorm in the later period of landfalling. Relevant scientific issues that need in-depth study and measures of improving numerical predictions are put forward, in order to provide reference for the improvement of the forecast of heavy rainfall associated with tropical cyclone (TC) landfalling in South China. The analysis pointed out that the vertical shear of the environmental wind field, the boundary of the low-level air mass (such as the boundary of the cold pool), the intrusion of dry and cold air, mesoscale convective systems (MCSs) and the local topography are important factors that cause the asymmetric distribution of precipitation of the landfalling TC in South China. The occurrence of continuous rainstorms in South China during the late period of landfall is often related to the increase in monsoon activity. The active southwest monsoon provides favorable conditions for the development of MCSs in rainstorm. MCSs feed back to the large-scale circulation through latent heat heating, which lead to the maintenance of TC vortex circulation and the southwest monsoon, and cause iterative development of MCSs, resulting in continued heavy rains. To further improve the forecast of the model, it is essential to investigate and evaluate the performance of the current model, carry out in-depth research on the related scientific issues, and then propose effective improvement plans.
In view of the outstanding problems in the precipitation and model forecasts of the landfalling typhoons in South China, this paper analyzes the current research of the asymmetry of the precipitation distribution of the landfalling typhoon and the mechanism of the continuous rainstorm in the later period of landfalling. Relevant scientific issues that need in-depth study and measures of improving numerical predictions are put forward, in order to provide reference for the improvement of the forecast of heavy rainfall associated with tropical cyclone (TC) landfalling in South China. The analysis pointed out that the vertical shear of the environmental wind field, the boundary of the low-level air mass (such as the boundary of the cold pool), the intrusion of dry and cold air, mesoscale convective systems (MCSs) and the local topography are important factors that cause the asymmetric distribution of precipitation of the landfalling TC in South China. The occurrence of continuous rainstorms in South China during the late period of landfall is often related to the increase in monsoon activity. The active southwest monsoon provides favorable conditions for the development of MCSs in rainstorm. MCSs feed back to the large-scale circulation through latent heat heating, which lead to the maintenance of TC vortex circulation and the southwest monsoon, and cause iterative development of MCSs, resulting in continued heavy rains. To further improve the forecast of the model, it is essential to investigate and evaluate the performance of the current model, carry out in-depth research on the related scientific issues, and then propose effective improvement plans.
Available online: May 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041201
Abstract:
The observation of the microstructure of rainfall is very important for the accurate prediction of precipitation. However, due to factors such as non-precipitation factors, turbulence and raindrop overlap, there are certain errors in the quality of the current raindrop spectrum observation data,, 9 national meteorological observation stations in Beijing were selected from the Parsivel disdrometer observation data from April to October 2017, combined with the tipping-bucket gauge rainfall observation data and manual records weather phenomenon, study the quality control method of disdrometer observation data. The results show that: The wrong disdrometer observation data is mainly caused by haze, sand and dust weather and insect activities. The particle velocity is mainly below 5m?s-1, and the drop size distribution is relatively scattered.Through the speed threshold and quantity threshold(STQT) quality control methods, the wrong disdrometer observation data can be effectively eliminated. When the 0.4 speed threshold coefficient and 0.7 quantity threshold are used respectively, the best threat score(TS) is 0.92. After using STQT method for disdrometer observation data quality control, the correlation coefficient between disdrometer observation precipitation and tipping-bucket gauge observation precipitation increased from 0.757 to 0.985.
The observation of the microstructure of rainfall is very important for the accurate prediction of precipitation. However, due to factors such as non-precipitation factors, turbulence and raindrop overlap, there are certain errors in the quality of the current raindrop spectrum observation data,, 9 national meteorological observation stations in Beijing were selected from the Parsivel disdrometer observation data from April to October 2017, combined with the tipping-bucket gauge rainfall observation data and manual records weather phenomenon, study the quality control method of disdrometer observation data. The results show that: The wrong disdrometer observation data is mainly caused by haze, sand and dust weather and insect activities. The particle velocity is mainly below 5m?s-1, and the drop size distribution is relatively scattered.Through the speed threshold and quantity threshold(STQT) quality control methods, the wrong disdrometer observation data can be effectively eliminated. When the 0.4 speed threshold coefficient and 0.7 quantity threshold are used respectively, the best threat score(TS) is 0.92. After using STQT method for disdrometer observation data quality control, the correlation coefficient between disdrometer observation precipitation and tipping-bucket gauge observation precipitation increased from 0.757 to 0.985.
Available online: May 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041202
Abstract:
Abstract: Based on the air-sounding data, the CIND3830-CC CINRAD data and surface meteorological data. Based on 21 hail weather processes in Pu "er during 2013 to 2020. Furthermore,Storm cells with hail diameter ≥20mm were defined as large hail storm cells, storm cells with diameter ≥5mm but < 20mm were defined as medium hail storm cells, storm cells with diameter < 5mm were defined as small hail storm cells (GB/T27957-2011). The results show that the forecast indexes as, (1) It is concluded that the hail storm monomer shared characteristics. High top and high bottom structure of the radar echo, it is height above 5 km and large echo gradient and CR≥55 dBz、VIL≥23 kg/m2、H45dBz≥7.5 km、H45 dBz-H0≥2.8 km. (2) VIL jumped phenomenon in a 67% hail storm monomer, and jumped phenomenon to the occurrence of hail early time 5 ~ 10 min. The magnitude of the jump, the greater the corresponding VIL is larger,and no jumped characteristics VIL is smaller of radar echo.(3) The hail storm monomer are obvious convergence characteristics and large hailstorm cells often have mesocyclone characteristics.(4) All the large hail storm monomer VIL/H significantly greater than that of medium and small hail storm monomer VIL/H. Most large hail storm monomer H50dBz-H-20 significantly greater than medium and small hail storm monomer.. Mature stage of large hail storm monomer duration is often significantly longer duration of medium and small hail storm monomer. (5) The echo overhang structure of large hail storm monomer is often more than the medium and small hail storm monomer,and DVIL monomer and the rotation speed is often greater than medium and small hail storm monomer. (6) ET no factor and identify different levels of identification of hail hail factor.
Abstract: Based on the air-sounding data, the CIND3830-CC CINRAD data and surface meteorological data. Based on 21 hail weather processes in Pu "er during 2013 to 2020. Furthermore,Storm cells with hail diameter ≥20mm were defined as large hail storm cells, storm cells with diameter ≥5mm but < 20mm were defined as medium hail storm cells, storm cells with diameter < 5mm were defined as small hail storm cells (GB/T27957-2011). The results show that the forecast indexes as, (1) It is concluded that the hail storm monomer shared characteristics. High top and high bottom structure of the radar echo, it is height above 5 km and large echo gradient and CR≥55 dBz、VIL≥23 kg/m2、H45dBz≥7.5 km、H45 dBz-H0≥2.8 km. (2) VIL jumped phenomenon in a 67% hail storm monomer, and jumped phenomenon to the occurrence of hail early time 5 ~ 10 min. The magnitude of the jump, the greater the corresponding VIL is larger,and no jumped characteristics VIL is smaller of radar echo.(3) The hail storm monomer are obvious convergence characteristics and large hailstorm cells often have mesocyclone characteristics.(4) All the large hail storm monomer VIL/H significantly greater than that of medium and small hail storm monomer VIL/H. Most large hail storm monomer H50dBz-H-20 significantly greater than medium and small hail storm monomer.. Mature stage of large hail storm monomer duration is often significantly longer duration of medium and small hail storm monomer. (5) The echo overhang structure of large hail storm monomer is often more than the medium and small hail storm monomer,and DVIL monomer and the rotation speed is often greater than medium and small hail storm monomer. (6) ET no factor and identify different levels of identification of hail hail factor.
Available online: May 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.032801
Abstract:
To study whether the phased array radar with high temporal and spatial resolution can accurately detect the evolution of heavy precipitation, the quality control of Foshan X-band phased array weather radar(PAWR) data was used to analyze a local short-time heavy rainfall occurred in Nanhai District of Foshan City, Guangdong Province on 4 September 2020. Analyzed the intensity field and three-dimensional wind field structure of multi-cell storms in Nanhai District from 16:00 to 17:30, and explored the relationship between the intensity field, three-dimensional wind field and precipitation. The results show that: (1) PAWR can provide more precise observations of severe convective weather. In the merging stage, the initiation, splitting and merging processes of multiple convective cells on a small scale and within a short period of time are observed. In the mature stage, the formation process of γ mesoscale cyclones is analyzed. The structural characteristics of the intensity field, three-dimensional wind field, divergence field and vorticity field during the cyclone convergence period is discussed. In the extinction stage, the structural characteristics of the formation and enhancement process of γ mesoscale anticyclones are analyzed. After the disappearance of cyclone and anticyclone, the convective cells rapidly die. (2) Based on the statistics obtained from the intensity field and three-dimensional wind field with high spatial and temporal resolution, it is found that the reflectivity factor and horizontal wind speed change significantly 10-15 minutes before the precipitation and 5-10 minutes before the maximum 5 minutes precipitation at automatic weather stations.The results of this study have a predictive effect on the monitoring and early warning of short-term heavy precipitation, and provide a reference for the phased array radar with high temporal and spatial resolution to finely detect the evolution of heavy precipitation.
To study whether the phased array radar with high temporal and spatial resolution can accurately detect the evolution of heavy precipitation, the quality control of Foshan X-band phased array weather radar(PAWR) data was used to analyze a local short-time heavy rainfall occurred in Nanhai District of Foshan City, Guangdong Province on 4 September 2020. Analyzed the intensity field and three-dimensional wind field structure of multi-cell storms in Nanhai District from 16:00 to 17:30, and explored the relationship between the intensity field, three-dimensional wind field and precipitation. The results show that: (1) PAWR can provide more precise observations of severe convective weather. In the merging stage, the initiation, splitting and merging processes of multiple convective cells on a small scale and within a short period of time are observed. In the mature stage, the formation process of γ mesoscale cyclones is analyzed. The structural characteristics of the intensity field, three-dimensional wind field, divergence field and vorticity field during the cyclone convergence period is discussed. In the extinction stage, the structural characteristics of the formation and enhancement process of γ mesoscale anticyclones are analyzed. After the disappearance of cyclone and anticyclone, the convective cells rapidly die. (2) Based on the statistics obtained from the intensity field and three-dimensional wind field with high spatial and temporal resolution, it is found that the reflectivity factor and horizontal wind speed change significantly 10-15 minutes before the precipitation and 5-10 minutes before the maximum 5 minutes precipitation at automatic weather stations.The results of this study have a predictive effect on the monitoring and early warning of short-term heavy precipitation, and provide a reference for the phased array radar with high temporal and spatial resolution to finely detect the evolution of heavy precipitation.
Available online: May 12, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.012701
Abstract:
How to evaluate the cloud seeding effect is a key issue of weather modification activities. This review summarizes the quantitative evaluation studies of artificial precipitation enhancement in China in recent years. The concept, approach, impact factors, and disadvantages of quantitative evaluation are systematic introduced. The increment rate in every literature is studied intensively to give a brief review of the quantitative evaluation of weather modification operations carried out in China. Moreover, some aspects for development and improvement of evaluation technology are discussed in detail to provide help and advice for future cloud seeding evaluation studies.
How to evaluate the cloud seeding effect is a key issue of weather modification activities. This review summarizes the quantitative evaluation studies of artificial precipitation enhancement in China in recent years. The concept, approach, impact factors, and disadvantages of quantitative evaluation are systematic introduced. The increment rate in every literature is studied intensively to give a brief review of the quantitative evaluation of weather modification operations carried out in China. Moreover, some aspects for development and improvement of evaluation technology are discussed in detail to provide help and advice for future cloud seeding evaluation studies.
Available online: May 11, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.040802
Abstract:
One supercell triggered severe thunderstorm gales in the Pearl River Delta on 11 April 2019 and another supercell induced an EF3 strong tornado in Xuwen County of Zhanjiang City on 13 April 2019.Based on multi-source observations,the synoptic situation,environmental conditions,structure of the storm,triggering characteristics of convective storm,and formation of the severe thunderstorm gale and tornado in two events are comparatively analyzed.The results are as follows.The severe thunderstorm gales occurred under the southward shear line in the lower layers and the surface cold front,which was classified as the baroclinic frontogenesis severe convection. The strong tornado was the southwest warm advection forcing sector severe convection.The environmental conditions for both days were characterized by strong 0-6 km vertical wind shear,low lifting condensation height and the stratification of ‘upper dry and lower wet’.But the sounding at Qingyuan on 11 April shows that 0-1 km vertical wind shear was small and average temperature dew point difference was 29.2 ℃ in middle levels.This condition was favorable for the formation of strong downdraft.However,the sounding at Haikou on 13 April shows that trong 0-1 km vertical wind shear was favorable for the tornado.On 11 April,the thunderstorm gales were located at the core of the supercell. The low-level mesocyclone was weaker and had a larger diameter of 6-7 km.The rotation depth of mesocyclone was below 2 km.On 13 April,the tornado occured at the top of the hook echo accompanied by low-level intense mesocyclone with the minimum diameter of 2 km and tornadic vortex signature.The rotation depth mesocyclone was up to 6 km.Vertical vorticity remained unchanged at the order of 10-2 s-1 before and after the thunderstorm gales.However,the tornado occurred during the magnitude of low-level mesocyclone vertical vorticity increased to be 10-1 s-1 rapidly,which was an order of magnitude larger than the vertical vorticity of strong thunderstorm gale event.The strong downdraft of the storm produced a large area of intense cold pool on the ground on 11 April,which was favorable for the formation of thunderstorm gales.The saturated atmosphere on the ground and the less strong downdraft of the storm were conducive to the occurrence of strong tornado.
One supercell triggered severe thunderstorm gales in the Pearl River Delta on 11 April 2019 and another supercell induced an EF3 strong tornado in Xuwen County of Zhanjiang City on 13 April 2019.Based on multi-source observations,the synoptic situation,environmental conditions,structure of the storm,triggering characteristics of convective storm,and formation of the severe thunderstorm gale and tornado in two events are comparatively analyzed.The results are as follows.The severe thunderstorm gales occurred under the southward shear line in the lower layers and the surface cold front,which was classified as the baroclinic frontogenesis severe convection. The strong tornado was the southwest warm advection forcing sector severe convection.The environmental conditions for both days were characterized by strong 0-6 km vertical wind shear,low lifting condensation height and the stratification of ‘upper dry and lower wet’.But the sounding at Qingyuan on 11 April shows that 0-1 km vertical wind shear was small and average temperature dew point difference was 29.2 ℃ in middle levels.This condition was favorable for the formation of strong downdraft.However,the sounding at Haikou on 13 April shows that trong 0-1 km vertical wind shear was favorable for the tornado.On 11 April,the thunderstorm gales were located at the core of the supercell. The low-level mesocyclone was weaker and had a larger diameter of 6-7 km.The rotation depth of mesocyclone was below 2 km.On 13 April,the tornado occured at the top of the hook echo accompanied by low-level intense mesocyclone with the minimum diameter of 2 km and tornadic vortex signature.The rotation depth mesocyclone was up to 6 km.Vertical vorticity remained unchanged at the order of 10-2 s-1 before and after the thunderstorm gales.However,the tornado occurred during the magnitude of low-level mesocyclone vertical vorticity increased to be 10-1 s-1 rapidly,which was an order of magnitude larger than the vertical vorticity of strong thunderstorm gale event.The strong downdraft of the storm produced a large area of intense cold pool on the ground on 11 April,which was favorable for the formation of thunderstorm gales.The saturated atmosphere on the ground and the less strong downdraft of the storm were conducive to the occurrence of strong tornado.
Available online: May 10, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.011502
Abstract:
Abstract: Deep learning has been developted at an unprecedend speed in radar extrapolation of forecasting, so objec-tive as-sessment of its applicability is an important prerequisites for operational applications. By utilizing the radar echo open data set of Guangdong-Hong Kong-Macao Greater Bay Area, the performances of 120-min radar echo ex-trapolation by recurrent convolutional neural network (ConvGRU) and fast dense optical flow method based on semi-lagrangian advection scheme (OF) have been compared and evaluated based on the echo morphology, probabil-ity of detection (POD), false alarm rate (FAR) and threat score (TS), the results show that the two methods all have effective extrapolation performance, they are not applicable to extrapolate the echo generation, enhancement and lo-cally dispersed, and the extrapolation effects are significantly affected by the type of weather processes. ConvGRU, poor in characterizing the refined motion pattern and evolution of the echoes, which may be more suitable for extrap-olating the main location of echoes with moderate distribution and simple motion, but the extrapolated echoes are with unstable intensity and blurred forms. OF, prone to large distribution deviations in the region with missing or sta-ble echoes, which is more suitable for extrapolating the strong echoes above 50 dBz and with better echoes structure. The number of samples, one of the most important elements to determine the model effectiveness, still is poor in this paper, which need to be further expanded for cover all kinds of weather processes comprehensively in actual forecast operation.
Abstract: Deep learning has been developted at an unprecedend speed in radar extrapolation of forecasting, so objec-tive as-sessment of its applicability is an important prerequisites for operational applications. By utilizing the radar echo open data set of Guangdong-Hong Kong-Macao Greater Bay Area, the performances of 120-min radar echo ex-trapolation by recurrent convolutional neural network (ConvGRU) and fast dense optical flow method based on semi-lagrangian advection scheme (OF) have been compared and evaluated based on the echo morphology, probabil-ity of detection (POD), false alarm rate (FAR) and threat score (TS), the results show that the two methods all have effective extrapolation performance, they are not applicable to extrapolate the echo generation, enhancement and lo-cally dispersed, and the extrapolation effects are significantly affected by the type of weather processes. ConvGRU, poor in characterizing the refined motion pattern and evolution of the echoes, which may be more suitable for extrap-olating the main location of echoes with moderate distribution and simple motion, but the extrapolated echoes are with unstable intensity and blurred forms. OF, prone to large distribution deviations in the region with missing or sta-ble echoes, which is more suitable for extrapolating the strong echoes above 50 dBz and with better echoes structure. The number of samples, one of the most important elements to determine the model effectiveness, still is poor in this paper, which need to be further expanded for cover all kinds of weather processes comprehensively in actual forecast operation.
Available online: May 09, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.040601
Abstract:
Based on reanalysis data, this research reveals the modulation of MJO on persistent precipitation in the Southern China during February-March 2019. Through analyzing the characteristics of precipitation, it is discovered that there are two obvious precipitation in the southern China, and the variation of precipitation is closely related to the evolution of the phase and amplitude of MJO. When the amplitude of MJO enhances (weakens) obviously, the anomalous precipitation in the Southern China increase (decrease). The persistent precipitation process is divided into two precipitation processes. In the first precipitation process, MJO is active in phases 8 and 1, and the precipitation was located in the total southern region. In the second precipitation process, MJO is active in phase 2-4, and the precipitation is mainly concentrated in South China, and the intensity of the precipitation was stronger. There are significant differences in the large-scale circulation and moisture transport between the two precipitation processes. In the first precipitation process, moisture convergence and upward movement occur in the total southern region. However, during the second precipitation, stronger moisture convergence and upward movement appear only in South China, which corresponds to stronger precipitation in South China during the second precipitation. Further diagnosis of moisture transport shows that in the first precipitation process, the zonal and meridional moisture convergence and meridional moisture advection play a leading role, while in the second precipitation process, only the meridional moisture convergence makes the largest contribution. It is worth noting that the contribution of low-frequency moisture advection by intraseasonal meridional wind is very crucial in both precipitation processes, which indicates that MJO can affect the precipitation in the southern region by regulating moiusture transport by intraseasonal meridional wind.
Based on reanalysis data, this research reveals the modulation of MJO on persistent precipitation in the Southern China during February-March 2019. Through analyzing the characteristics of precipitation, it is discovered that there are two obvious precipitation in the southern China, and the variation of precipitation is closely related to the evolution of the phase and amplitude of MJO. When the amplitude of MJO enhances (weakens) obviously, the anomalous precipitation in the Southern China increase (decrease). The persistent precipitation process is divided into two precipitation processes. In the first precipitation process, MJO is active in phases 8 and 1, and the precipitation was located in the total southern region. In the second precipitation process, MJO is active in phase 2-4, and the precipitation is mainly concentrated in South China, and the intensity of the precipitation was stronger. There are significant differences in the large-scale circulation and moisture transport between the two precipitation processes. In the first precipitation process, moisture convergence and upward movement occur in the total southern region. However, during the second precipitation, stronger moisture convergence and upward movement appear only in South China, which corresponds to stronger precipitation in South China during the second precipitation. Further diagnosis of moisture transport shows that in the first precipitation process, the zonal and meridional moisture convergence and meridional moisture advection play a leading role, while in the second precipitation process, only the meridional moisture convergence makes the largest contribution. It is worth noting that the contribution of low-frequency moisture advection by intraseasonal meridional wind is very crucial in both precipitation processes, which indicates that MJO can affect the precipitation in the southern region by regulating moiusture transport by intraseasonal meridional wind.
Available online: April 28, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.041002
Abstract:
In order to study the echo characteristics of short-term heavy rainfall in the process of severe rainstorm in Changjiang River Basin, using the data of weather, radar echo and meteorological and hydrological rainfall in Changjiang River Basin, 10 severe rainstorm processes in Changjiang River Basin from 2000 to 2020 (21 years) are studied by using the methods of Meteorology, statistics, radar meteorology and image processing, The results show that: (1) the intensity of severe rainstorm depends on the precipitation intensity, temporal and spatial distribution of precipitation and the number of stations. When the 3h cumulative rainfall is ≥ 100 mm / 3h and other conditions are met, the red early warning of severe rainstorm can be issued. Grasping the monitoring and early warning of 3h short-term heavy precipitation is the key to do a good job in the prediction service of severe rainstorm. (2) Ultra low level jet, middle and low level vortex, high-altitude low trough, low-level convergence and high-level divergence played an important role in the process of severe rainstorm in Jingdezhen city. (3) Heavy precipitation is caused by flocculent strong echo monomer, strong echo short band or other echoes in large-scale mixed precipitation, and the echo intensity is 45 ~ 55 dBZ. (4) STI product information can not only reflect the movement information of strong echo, but also analyze the convergence of echo, which has a good reference value for short-term and imminent prediction. On the echo band covering Jiangxi wide Guangdong West direction, there are many short band echoes in south-north direction, which move from west to east to form "train effect". The vertical velocity W of wind profile radar product can roughly reflect the echo movement. (5) The CR intensity causing the heavy rain is mostly 45 ~ 50 dBZ, the average top height of ET is 12 ~ 13 km, the VIL is 5 ~ 10 kg / m2, and the average extension height of strong echo of 45 dBZ is 6 km. (6) When the CR intensity is above 45 dBZ: the strong echo area reaches grade 3, and there is a great possibility of short-term heavy precipitation; The strong echo area is in grade 2, mostly between 20 ~ 30 mm / h; When the strong echo area is at level 1, the precipitation intensity is basically below 20 mm / h. These research results provide a reference basis for understanding, monitoring and early warning the echo characteristics and prediction of short-term heavy precipitation in severe rainstorm in Changjiang basin.
In order to study the echo characteristics of short-term heavy rainfall in the process of severe rainstorm in Changjiang River Basin, using the data of weather, radar echo and meteorological and hydrological rainfall in Changjiang River Basin, 10 severe rainstorm processes in Changjiang River Basin from 2000 to 2020 (21 years) are studied by using the methods of Meteorology, statistics, radar meteorology and image processing, The results show that: (1) the intensity of severe rainstorm depends on the precipitation intensity, temporal and spatial distribution of precipitation and the number of stations. When the 3h cumulative rainfall is ≥ 100 mm / 3h and other conditions are met, the red early warning of severe rainstorm can be issued. Grasping the monitoring and early warning of 3h short-term heavy precipitation is the key to do a good job in the prediction service of severe rainstorm. (2) Ultra low level jet, middle and low level vortex, high-altitude low trough, low-level convergence and high-level divergence played an important role in the process of severe rainstorm in Jingdezhen city. (3) Heavy precipitation is caused by flocculent strong echo monomer, strong echo short band or other echoes in large-scale mixed precipitation, and the echo intensity is 45 ~ 55 dBZ. (4) STI product information can not only reflect the movement information of strong echo, but also analyze the convergence of echo, which has a good reference value for short-term and imminent prediction. On the echo band covering Jiangxi wide Guangdong West direction, there are many short band echoes in south-north direction, which move from west to east to form "train effect". The vertical velocity W of wind profile radar product can roughly reflect the echo movement. (5) The CR intensity causing the heavy rain is mostly 45 ~ 50 dBZ, the average top height of ET is 12 ~ 13 km, the VIL is 5 ~ 10 kg / m2, and the average extension height of strong echo of 45 dBZ is 6 km. (6) When the CR intensity is above 45 dBZ: the strong echo area reaches grade 3, and there is a great possibility of short-term heavy precipitation; The strong echo area is in grade 2, mostly between 20 ~ 30 mm / h; When the strong echo area is at level 1, the precipitation intensity is basically below 20 mm / h. These research results provide a reference basis for understanding, monitoring and early warning the echo characteristics and prediction of short-term heavy precipitation in severe rainstorm in Changjiang basin.
Available online: April 11, 2022 , DOI: 1000-0526.2022. 032102
Abstract:
Using the vorticity-related data on the gradient observation tower in the Wuying Forest Ecological Monitoring Station of China Meteorological Administration, this paper deal with the turbulence characteristics of the underlying surface of the forest (turbulence intensity, turbulence variance, etc.), and calculate the zero-plane displacement d, the roughness length z0 and the momentum drag coefficient CD. The result indicates that southwest wind prevails throughout the year, with northeast wind only in summer. Strong tubulence intensity during the growing season (May-September), weaker turbulence intensity during the non-growing season(October-April), the average turbulence intensity of the horizontal wind speed is 0.4, and the vertical wind speed is 0.16. Both the zero-plane displacement d and the roughness length z0 have obvious seasonal changes, and they consistently show a trend of high in the growing season and low in the non-growing season, the average values of d and z0 are 18.56 m and 1.21 m, respectively. Under unstable conditions, the standard deviation of wind speed all conform to the 1/3 similar laws; neutral conditions in spring, the dimensionless three-dimensional wind speed standard deviation σi/u*(i=u,v,w) are 2.81, 2.73, 1.20; 2.62, 2.53, 1.10 in summer; 2.62, 2.53, 1.10 in summer; 2.63, 2.51, 1.14 in autumn; 2.74, 2.54, 1.17 in winter. The variances of temperature and humidity conformed to similar laws under unstable conditions, the coefficients for spring fitting are 2.06 and 2.67, 2.46 and 2.18 in summer, 1.94 and 2.85 in autumn, 1.96 and 3.00 in winter.CD reaches its peak in weak instability, and the overall average is 9.8×10-3, increases approximately linearly with roughness.
Using the vorticity-related data on the gradient observation tower in the Wuying Forest Ecological Monitoring Station of China Meteorological Administration, this paper deal with the turbulence characteristics of the underlying surface of the forest (turbulence intensity, turbulence variance, etc.), and calculate the zero-plane displacement d, the roughness length z0 and the momentum drag coefficient CD. The result indicates that southwest wind prevails throughout the year, with northeast wind only in summer. Strong tubulence intensity during the growing season (May-September), weaker turbulence intensity during the non-growing season(October-April), the average turbulence intensity of the horizontal wind speed is 0.4, and the vertical wind speed is 0.16. Both the zero-plane displacement d and the roughness length z0 have obvious seasonal changes, and they consistently show a trend of high in the growing season and low in the non-growing season, the average values of d and z0 are 18.56 m and 1.21 m, respectively. Under unstable conditions, the standard deviation of wind speed all conform to the 1/3 similar laws; neutral conditions in spring, the dimensionless three-dimensional wind speed standard deviation σi/u*(i=u,v,w) are 2.81, 2.73, 1.20; 2.62, 2.53, 1.10 in summer; 2.62, 2.53, 1.10 in summer; 2.63, 2.51, 1.14 in autumn; 2.74, 2.54, 1.17 in winter. The variances of temperature and humidity conformed to similar laws under unstable conditions, the coefficients for spring fitting are 2.06 and 2.67, 2.46 and 2.18 in summer, 1.94 and 2.85 in autumn, 1.96 and 3.00 in winter.CD reaches its peak in weak instability, and the overall average is 9.8×10-3, increases approximately linearly with roughness.
Available online: April 02, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.083101
Abstract:
A comparison of two rainstorms ocurred in June 2001 and July 1986 (hereafter “01.6” and “86.7”) related to distant typhoons affecting Jiangsu Province during Mei-yu period shows that: (1) For “01.6”, the precipitation duration is shorter, the precipitation area is motionless, the rainfall intensity is stronger. For “86.7”, the precipitation duration is longer, the precipitation area moves from north to south, the rainfall intensity is weaker. (2) In terms of atmospheric circulations, during “01.6” process, the subtropical high extends significantly to the north. The northward extended inverted trough of typhoon and low level jet form the low-level convergence and transport warm and moist air together. The low-pressure troughs at middle- and upper-level are stable. The influence of upper-level cold air is weaker. During “86.7” process, the northward extension and impact of typhoon’s inverted trough are weaker. The convergence of low-level wind and the transportation of warm and humid air flow rely?more?on low-level jet than on typhoon’s inverted trough. The low-pressure troughs at middle- and upper- level both move eastward and southward quickly. The influence of upper-level cold air is strong. (3) In terms of dynamical analysis, the high-level divergence and low-level convergence of “01.6” process are more intense, the coupling of positive vorticity at lower level and negative vorticity at upper level is more stable and deep, the non-geostrophic wet Q vector convergence is stronger, and all these dynamic processes stay over the southeastern part of Jiangsu. For “86.7”, the dynamic processes are weaker. The coupling of divergence and vertical vorticity move from north-central Jiangsu to the southeastern part of Jiangsu. The non-geostrophic Q vector convergence zone covers eastern part of Jiangsu. (4) Compared with “86.7”, the low level water vapor flux convergence of “01.6” is stronger. The air over the rainstorm area of “01.6” is more saturated. The deep saturated layer “01.6” is formed earlier, and maintain longer. (5) In terms of thermodynamical analysis, the convective instability of middle- and lower-level atmosphere is stronger, but the E index and E index increment of “01.6” are greater, which demonstrates that the middle- and low-level atmosphere contains more energy and water vapor.
A comparison of two rainstorms ocurred in June 2001 and July 1986 (hereafter “01.6” and “86.7”) related to distant typhoons affecting Jiangsu Province during Mei-yu period shows that: (1) For “01.6”, the precipitation duration is shorter, the precipitation area is motionless, the rainfall intensity is stronger. For “86.7”, the precipitation duration is longer, the precipitation area moves from north to south, the rainfall intensity is weaker. (2) In terms of atmospheric circulations, during “01.6” process, the subtropical high extends significantly to the north. The northward extended inverted trough of typhoon and low level jet form the low-level convergence and transport warm and moist air together. The low-pressure troughs at middle- and upper-level are stable. The influence of upper-level cold air is weaker. During “86.7” process, the northward extension and impact of typhoon’s inverted trough are weaker. The convergence of low-level wind and the transportation of warm and humid air flow rely?more?on low-level jet than on typhoon’s inverted trough. The low-pressure troughs at middle- and upper- level both move eastward and southward quickly. The influence of upper-level cold air is strong. (3) In terms of dynamical analysis, the high-level divergence and low-level convergence of “01.6” process are more intense, the coupling of positive vorticity at lower level and negative vorticity at upper level is more stable and deep, the non-geostrophic wet Q vector convergence is stronger, and all these dynamic processes stay over the southeastern part of Jiangsu. For “86.7”, the dynamic processes are weaker. The coupling of divergence and vertical vorticity move from north-central Jiangsu to the southeastern part of Jiangsu. The non-geostrophic Q vector convergence zone covers eastern part of Jiangsu. (4) Compared with “86.7”, the low level water vapor flux convergence of “01.6” is stronger. The air over the rainstorm area of “01.6” is more saturated. The deep saturated layer “01.6” is formed earlier, and maintain longer. (5) In terms of thermodynamical analysis, the convective instability of middle- and lower-level atmosphere is stronger, but the E index and E index increment of “01.6” are greater, which demonstrates that the middle- and low-level atmosphere contains more energy and water vapor.
Available online: April 02, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.080501
Abstract:
Using daily encrypt upper data at 07:00 and 19:00(Beijing time) every 50 m ,the ground wind-sand data from Dunhuang, Jiuquan, Zhangye and Minqin stations over Hexi Corridor in the spring of 2006-2016 , variation characteristics of vertical structure in atmospheric boundary layer of dust intensity at different stations, daily change and duration of dust storm as well as dust storms under different circulation situations were analyzed from ground to 5km above ground level. The results showed that: (1) Inverse temperature intensity of sandstorm at 07:00 was above 1.6℃/100 m, the dry layer thickness of less than 40% relative humidity was more than 3 Km, the dry layer thickness of less than 30% relative humidity was more than 1.5 Km ,the maximum wind speed at 19:00 was more than 13 m/s;(2)Due to the influence of altitude, topography and underlying soil properties, the lower wind field has obvious diurnal variation and valley wind effect. It was high temperature, dry air, big wind speed and more dust in Dunhuang and Minqin;Zhangye has larger wind speed that affected by the narrow tube effect in the corridor; the lower air layer of Dunhuang was mainly southeast wind to southwest wind, but its upper level and other stations were mainly west wind to northwest wind. For daily variation of meteorological conditions in the boundary layer at the time of sandstorm:it was dry and warm in morning, but wet,cold and big wind speed in afternoon , the maximum wind speed was 17.6 m/s occurred at height of 0.9 Km ; south wind occurred near ground from night to morning, west wind occurred in afternoon ,dry and small wind speed occurred in evening ;(3) When the sandstorm last for a long time, the temperature was low in the morning and evening, and the dry layer of the atmosphere whose relative humidity ≤30% was 2.85 km thick at 07:00 in less than 5 hours, while 1.05 Km thick at 19:00 in more than 5 hours, it was thicker in the morning and night, shallow in the afternoon, that minimum threshold of temperature dew point difference was 16-17℃, maximum height was 2.85-3 km;（4）Under different sand storm circulation conditions, ridge type was dry and cold in the morning,the maximum wind speed was 14.6m/s at 0.75 km height; trough type was wet, cold and big wind speed in the afternoon,the maximum wind speed was 15.7m/s at 0.9 km height; westerly type was dry, cold and small wind speed near the ground, but wind speed were bigger between 1.2-3.5km height in the morning and higher than 2.4km in the evening.
Using daily encrypt upper data at 07:00 and 19:00(Beijing time) every 50 m ,the ground wind-sand data from Dunhuang, Jiuquan, Zhangye and Minqin stations over Hexi Corridor in the spring of 2006-2016 , variation characteristics of vertical structure in atmospheric boundary layer of dust intensity at different stations, daily change and duration of dust storm as well as dust storms under different circulation situations were analyzed from ground to 5km above ground level. The results showed that: (1) Inverse temperature intensity of sandstorm at 07:00 was above 1.6℃/100 m, the dry layer thickness of less than 40% relative humidity was more than 3 Km, the dry layer thickness of less than 30% relative humidity was more than 1.5 Km ,the maximum wind speed at 19:00 was more than 13 m/s;(2)Due to the influence of altitude, topography and underlying soil properties, the lower wind field has obvious diurnal variation and valley wind effect. It was high temperature, dry air, big wind speed and more dust in Dunhuang and Minqin;Zhangye has larger wind speed that affected by the narrow tube effect in the corridor; the lower air layer of Dunhuang was mainly southeast wind to southwest wind, but its upper level and other stations were mainly west wind to northwest wind. For daily variation of meteorological conditions in the boundary layer at the time of sandstorm:it was dry and warm in morning, but wet,cold and big wind speed in afternoon , the maximum wind speed was 17.6 m/s occurred at height of 0.9 Km ; south wind occurred near ground from night to morning, west wind occurred in afternoon ,dry and small wind speed occurred in evening ;(3) When the sandstorm last for a long time, the temperature was low in the morning and evening, and the dry layer of the atmosphere whose relative humidity ≤30% was 2.85 km thick at 07:00 in less than 5 hours, while 1.05 Km thick at 19:00 in more than 5 hours, it was thicker in the morning and night, shallow in the afternoon, that minimum threshold of temperature dew point difference was 16-17℃, maximum height was 2.85-3 km;（4）Under different sand storm circulation conditions, ridge type was dry and cold in the morning,the maximum wind speed was 14.6m/s at 0.75 km height; trough type was wet, cold and big wind speed in the afternoon,the maximum wind speed was 15.7m/s at 0.9 km height; westerly type was dry, cold and small wind speed near the ground, but wind speed were bigger between 1.2-3.5km height in the morning and higher than 2.4km in the evening.
Available online: April 02, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.031001
Abstract:
Weather radar is the cornerstone of nowcasting. Weather radar is the cornerstone of nowcasting. In this paper, radar parameters are extracted from weather radar and radiosonde data, and by using thunderstorm identification extrapolation techniques.Compared the differences between the probability density function and membership degree characteristics when there is and no cloud-to-ground lightning, an early warning method for near-1h cloud-to-ground lightning based on fuzzy logical algorithm was established. The results show that the maximum echo intensity and the echo top height ET of -10℃~ -25℃ height layer are the best factors for the early warning of lightning in Hubei province, especially REF-15℃, REF-20℃ and REF-25℃ are best ones, REF-10℃ is the second one, and it has less significance for lightning indication. According to the different contribution of different factors, the unequal weight distribution is given, and the dynamic weight coefficient is used to refine the distribution of lightning samples. In view of the results of 1-hour (6-minute interval) prediction and the actual situation, the hit rate of POD can reach 50% and the critical success index of CSI is about 30% in 30 minutes, pod and CSI decrease slowly with the forecast time. Through a case study, it is found that the method has a higher forecast score in large-scale thunderstorm weather and a lower forecast score in local convection. This work shows that the method based on radar parameters is basically reasonable and reliable, and can be used in Hubei lightning short-term automatic forecasting, early warning and decision-making services.
Weather radar is the cornerstone of nowcasting. Weather radar is the cornerstone of nowcasting. In this paper, radar parameters are extracted from weather radar and radiosonde data, and by using thunderstorm identification extrapolation techniques.Compared the differences between the probability density function and membership degree characteristics when there is and no cloud-to-ground lightning, an early warning method for near-1h cloud-to-ground lightning based on fuzzy logical algorithm was established. The results show that the maximum echo intensity and the echo top height ET of -10℃~ -25℃ height layer are the best factors for the early warning of lightning in Hubei province, especially REF-15℃, REF-20℃ and REF-25℃ are best ones, REF-10℃ is the second one, and it has less significance for lightning indication. According to the different contribution of different factors, the unequal weight distribution is given, and the dynamic weight coefficient is used to refine the distribution of lightning samples. In view of the results of 1-hour (6-minute interval) prediction and the actual situation, the hit rate of POD can reach 50% and the critical success index of CSI is about 30% in 30 minutes, pod and CSI decrease slowly with the forecast time. Through a case study, it is found that the method has a higher forecast score in large-scale thunderstorm weather and a lower forecast score in local convection. This work shows that the method based on radar parameters is basically reasonable and reliable, and can be used in Hubei lightning short-term automatic forecasting, early warning and decision-making services.
Available online: March 09, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.010601
Abstract:
With the bright prospects of application of large unmanned aerial vehicles(UAV) in artificial precipitation enhancement operation, an UAV artificial precipitation enhancement experiment was carried out in Qilian Mountains. This paper discussed the UAV operating performance and analyzed the change characteristics of the microphysical parameters during the cloud seeding processes on October 27, 2020. The results showed that: the UAV had the ability of large-scale artificial precipitation enhancement and detection with more than 5 hours’ endurance and good anti-deicing and crosswind capabilities. After the cloud seeding processes, concentration and diameter of cloud particles increased in every level, and the concentration of low-level cloud particles is significantly higher than that of high-level. The change of cloud microphysical characteristics before and after seeding operation was related to cloud position and time to select. Within 20-30 minutes after the seeding, the concentration of the number of raindrops at the ground decreased at first and then increased, while the effective diameter of the particles continued to increase; the cloud particle spectrum showed the characteristics of an increase in large cloud particles, the precipitation particle spectrum was broadened.
With the bright prospects of application of large unmanned aerial vehicles(UAV) in artificial precipitation enhancement operation, an UAV artificial precipitation enhancement experiment was carried out in Qilian Mountains. This paper discussed the UAV operating performance and analyzed the change characteristics of the microphysical parameters during the cloud seeding processes on October 27, 2020. The results showed that: the UAV had the ability of large-scale artificial precipitation enhancement and detection with more than 5 hours’ endurance and good anti-deicing and crosswind capabilities. After the cloud seeding processes, concentration and diameter of cloud particles increased in every level, and the concentration of low-level cloud particles is significantly higher than that of high-level. The change of cloud microphysical characteristics before and after seeding operation was related to cloud position and time to select. Within 20-30 minutes after the seeding, the concentration of the number of raindrops at the ground decreased at first and then increased, while the effective diameter of the particles continued to increase; the cloud particle spectrum showed the characteristics of an increase in large cloud particles, the precipitation particle spectrum was broadened.
Available online: March 01, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.013001
Abstract:
Under the similar atmospheric circulation background, the precipitation characteristics along the coast of Guangdong on June 2 and June 3, 2020 are quite different, its mechanism is worthy of in depth exploration. Based on ERA5 reanalysis data, wind profile radar products and observation data, the differences of precipitation, atmospheric circulation and physical quantity field in the warm coastal sector of western Guangdong in the past two days are compared and analyzed, and the trigger and maintenance mechanism of double low-level jets on precipitation in the warm sector of the region is discussed. The main conclusions are as follows: when the low-level southwest jet axis is located in eastern Guangxi, the boundary layer southerly jet over the northwest of the South China Sea strengthens at night, and its front side reaches the coast of western Guangdong and maintains for a long time, the dynamic convergence and uplift caused by the convergence of wind speed in front of the boundary layer southerly jet and the blocking effect of the coastal terrain of western Guangdong on the southward flow are conducive to the triggering of convection in this area, At the same time, the existence and maintenance of cold pool is conducive to the development and maintenance of rainstorm in the warm coastal sector of western Guangdong. When the low-level jet is significantly strengthened, expands to the east and retracts to the north, and the boundary layer jet turns to the southwest and extends to the north of the Pearl River Delta, it is not conducive to the triggering and development of convection in the west coast of Guangdong.
Under the similar atmospheric circulation background, the precipitation characteristics along the coast of Guangdong on June 2 and June 3, 2020 are quite different, its mechanism is worthy of in depth exploration. Based on ERA5 reanalysis data, wind profile radar products and observation data, the differences of precipitation, atmospheric circulation and physical quantity field in the warm coastal sector of western Guangdong in the past two days are compared and analyzed, and the trigger and maintenance mechanism of double low-level jets on precipitation in the warm sector of the region is discussed. The main conclusions are as follows: when the low-level southwest jet axis is located in eastern Guangxi, the boundary layer southerly jet over the northwest of the South China Sea strengthens at night, and its front side reaches the coast of western Guangdong and maintains for a long time, the dynamic convergence and uplift caused by the convergence of wind speed in front of the boundary layer southerly jet and the blocking effect of the coastal terrain of western Guangdong on the southward flow are conducive to the triggering of convection in this area, At the same time, the existence and maintenance of cold pool is conducive to the development and maintenance of rainstorm in the warm coastal sector of western Guangdong. When the low-level jet is significantly strengthened, expands to the east and retracts to the north, and the boundary layer jet turns to the southwest and extends to the north of the Pearl River Delta, it is not conducive to the triggering and development of convection in the west coast of Guangdong.
Abstract:
Based on the rainfall data of the middle and lower reaches of the Yangtze River(MLRYR) during Meiyu season(MYS), NCEP/NCAR daily reanalysis data, NOAA monthly average sea surface temperature(SST) and Arctic sea ice(ASI) indices data, the circulation characteristics and precursory signals of the abnormal rainfall in MLRYR after 2000 were studied by correlation, regression and other methods. A prediction model was established and a prediction experiment was carried out. Results show that when there is more precipitation in MLRYR, the low-value systems near Balkhash Lake and Bohai Bay in the Eurasian mid-latitudes are more active. The upper-level westerly jet stream is southward and eastward, the low-level wind field distributed in meridional wave train, the East Asian summer monsoon weaker, and the Meiyu front is strong in the area from the Sea of Japan to MLRYR,there is anticyclone anomaly circulation over South China Sea, which results in strong ascending motion and convergence of water vapor flux over MLRYR, and thus increasing the rainfall therein. The anomalous SST over tropical eastern Pacific (TEP) and ASI in previous winter are the main precursors of abnormal Meiyu rainfall over MLRYR. The anomalous anticyclone over South China Sea during MYS induced by the positive phase of SST over TEP and ASI are beneficial to the convergence of cold air and warm moist air over MLRYR. As a result, the rainfall over MLRYR increases. The SST and ASI factors are used to construct the rainfall multiple regression prediction model over MLRYR during MYS, the results of fitting and prediction well Reflect real situations.
Based on the rainfall data of the middle and lower reaches of the Yangtze River(MLRYR) during Meiyu season(MYS), NCEP/NCAR daily reanalysis data, NOAA monthly average sea surface temperature(SST) and Arctic sea ice(ASI) indices data, the circulation characteristics and precursory signals of the abnormal rainfall in MLRYR after 2000 were studied by correlation, regression and other methods. A prediction model was established and a prediction experiment was carried out. Results show that when there is more precipitation in MLRYR, the low-value systems near Balkhash Lake and Bohai Bay in the Eurasian mid-latitudes are more active. The upper-level westerly jet stream is southward and eastward, the low-level wind field distributed in meridional wave train, the East Asian summer monsoon weaker, and the Meiyu front is strong in the area from the Sea of Japan to MLRYR,there is anticyclone anomaly circulation over South China Sea, which results in strong ascending motion and convergence of water vapor flux over MLRYR, and thus increasing the rainfall therein. The anomalous SST over tropical eastern Pacific (TEP) and ASI in previous winter are the main precursors of abnormal Meiyu rainfall over MLRYR. The anomalous anticyclone over South China Sea during MYS induced by the positive phase of SST over TEP and ASI are beneficial to the convergence of cold air and warm moist air over MLRYR. As a result, the rainfall over MLRYR increases. The SST and ASI factors are used to construct the rainfall multiple regression prediction model over MLRYR during MYS, the results of fitting and prediction well Reflect real situations.
Abstract:
Based on the observational and NCEP reanalysis data, the frontogenesis and instabilities in two continuous autumn torrential rain days that occurred in Henan province in September, 2011 are diagnosed. The results show that there exists a frontal zone which is from northeast to southwest in north central Henan province in the two torrential rain days. The frontal zone shows the characteristic of quasi-stationary. The similarities between the frontogenetical functions of two days are, before the heavy rain, frontogenesis is demonstrated in most part of frontal zone; in the occurrence of heavy rain, frontogenesis gets strengthened in high and low levels while weakened in middle level of 500-600 hPa and even frontolysis is appeared at about 400hPa, this is caused by the strengthening of vertical motion; when the heavy rain gets weak, frontogenesis in high level and frontolysis area both descend in height, this is corresponding to the weakening of vertical motion. The differences are, the middle tropospheric frontal zone is stiff during the night of the second torrential rain day, frontogenesis centers are getting near to warm region, it is the result of strengthening of convective rainfall and enhancement of precipitation efficiency and condensation latent heat release. The roles of terms of frontogenetical function are different. The contribution of deformation process to forntogenesis is greatest; the contribution of tilting term is mainly frontolysis. The strong frontolysis center at 400hPa during heavy rain is the distinct manifestation of contribution of tilting term. The two torrential rain days are both of inertial stability. The first day is convective stable but symmetric instable, so the rainfall band is the result of symmetric instability. In the second day, convective instability and symmetric instability are coexisted at about 700hPa in frontal zone, so the rainfall band is the result of convective-symmetric instabilities and thunderstorms during the night are of the characteristics of elevated thunderstorms. Furthermore, in the first torrential rain day, there exists consistent slanted upward flow in the warm side of frontal zone; frontogenesis center, symmetric instability center and upward motion center appear together, it shows that frontogenesis provides an advantage for the release of symmetric instability. In the second torrential rain day, there exists an obvious mixture of slanted convection and vertical convection; the starting point of vertical upward flow is just the convective-symmetric instabilities area. Vertical upward flow is stronger than the slanted upward flow in the first day, it shows that gravitational convection is dominative.
Based on the observational and NCEP reanalysis data, the frontogenesis and instabilities in two continuous autumn torrential rain days that occurred in Henan province in September, 2011 are diagnosed. The results show that there exists a frontal zone which is from northeast to southwest in north central Henan province in the two torrential rain days. The frontal zone shows the characteristic of quasi-stationary. The similarities between the frontogenetical functions of two days are, before the heavy rain, frontogenesis is demonstrated in most part of frontal zone; in the occurrence of heavy rain, frontogenesis gets strengthened in high and low levels while weakened in middle level of 500-600 hPa and even frontolysis is appeared at about 400hPa, this is caused by the strengthening of vertical motion; when the heavy rain gets weak, frontogenesis in high level and frontolysis area both descend in height, this is corresponding to the weakening of vertical motion. The differences are, the middle tropospheric frontal zone is stiff during the night of the second torrential rain day, frontogenesis centers are getting near to warm region, it is the result of strengthening of convective rainfall and enhancement of precipitation efficiency and condensation latent heat release. The roles of terms of frontogenetical function are different. The contribution of deformation process to forntogenesis is greatest; the contribution of tilting term is mainly frontolysis. The strong frontolysis center at 400hPa during heavy rain is the distinct manifestation of contribution of tilting term. The two torrential rain days are both of inertial stability. The first day is convective stable but symmetric instable, so the rainfall band is the result of symmetric instability. In the second day, convective instability and symmetric instability are coexisted at about 700hPa in frontal zone, so the rainfall band is the result of convective-symmetric instabilities and thunderstorms during the night are of the characteristics of elevated thunderstorms. Furthermore, in the first torrential rain day, there exists consistent slanted upward flow in the warm side of frontal zone; frontogenesis center, symmetric instability center and upward motion center appear together, it shows that frontogenesis provides an advantage for the release of symmetric instability. In the second torrential rain day, there exists an obvious mixture of slanted convection and vertical convection; the starting point of vertical upward flow is just the convective-symmetric instabilities area. Vertical upward flow is stronger than the slanted upward flow in the first day, it shows that gravitational convection is dominative.
Abstract:
Using the observation data of Ka band scanning millimeter-wave radar and automatic weather station, the sea fog remote sensing experiment was carried out in coastal area of Pingtan, Fujian Province. The characteristics of six sea fog processes occurred during the May 2020 to March 2021 were analyzed, and visibility inversion in fog area was carried out based on millimeter-wave radar. The results show that :(1) Millimeter-wave radar could effectively detect the horizontal distribution and vertical structure of sea fog, and could be used to monitor the evolution of sea fog. (2) In the flourishing stage of sea fog, the reflectivity factor of millimeter-wave radar showed a strong filamile-like echo structure extending from the top of fog layer to the surface, and the echo intensity of bottom layer was larger than that of upper layer. (3) The radar reflectivity factor of sea fog was negatively correlated with the forward-scatter visibility, but for each sea fog process, between the radar reflectivity factor and forward scatter visibility did not follow a clear general equation. (4) The radar reflectance factor of sea fog was concentrated in the range from -30 to -10dBZ, and the frequency histogram accords with normal distribution. The echo of fog area was uniform on the whole, but the dynamic range of reflectance factor was large in fog generation and dissipation stage, while the dynamic range was small in fog persistence stage. (5) Millimeter-wave radar inversion visibility and forward dispersion visibility have relatively consistent fluctuations, which could reflect the change of visibility in fog area, but different sample processes present differences.
Using the observation data of Ka band scanning millimeter-wave radar and automatic weather station, the sea fog remote sensing experiment was carried out in coastal area of Pingtan, Fujian Province. The characteristics of six sea fog processes occurred during the May 2020 to March 2021 were analyzed, and visibility inversion in fog area was carried out based on millimeter-wave radar. The results show that :(1) Millimeter-wave radar could effectively detect the horizontal distribution and vertical structure of sea fog, and could be used to monitor the evolution of sea fog. (2) In the flourishing stage of sea fog, the reflectivity factor of millimeter-wave radar showed a strong filamile-like echo structure extending from the top of fog layer to the surface, and the echo intensity of bottom layer was larger than that of upper layer. (3) The radar reflectivity factor of sea fog was negatively correlated with the forward-scatter visibility, but for each sea fog process, between the radar reflectivity factor and forward scatter visibility did not follow a clear general equation. (4) The radar reflectance factor of sea fog was concentrated in the range from -30 to -10dBZ, and the frequency histogram accords with normal distribution. The echo of fog area was uniform on the whole, but the dynamic range of reflectance factor was large in fog generation and dissipation stage, while the dynamic range was small in fog persistence stage. (5) Millimeter-wave radar inversion visibility and forward dispersion visibility have relatively consistent fluctuations, which could reflect the change of visibility in fog area, but different sample processes present differences.
Abstract:
Since the meridional positions of the east and west part of Western Pacific Subtropical High (WPSH) affect the climate over China differently, we re-defined the meridional index of WPSH in this study. The mean latitude of the location of 500 hPa geopotential height maximum along several meridian in 10°N-60°N, 110°E-130°E and 10°N-60°N, 130°E-150°E is defined as new west index (Index_NEW_west) and new east index (Index_NEW_east), respectively. Their average value is defined as new meridional index of WPSH (Index_NEW). The correlation between the indices and summer precipitation over eastern China is more significant than the ridge index defined by National Climate Center (Index_NCC), specifically for the positive correlation between Index_NEW_west and precipitation over North China plain. The negative correlation between Index_NEW_east and precipitation over Yangtze River basin is similar to that of Index_NCC. Regression of the 500 hPa horizontal wind with respect to Index_NEW_west (Index_NEW_east) presents anticyclonic circulation over western North Pacific and the anticyclone center locates near 38°N,130°E (40°N,145°E). The various collocations between north/south anomalies of Index_NEW_west/Index_NEW_east correspond to four types of rainfall patterns. The good relationship between the interannual variation of new indices and summer precipitation over eastern China provides more valuable reference for the study of precipitation prediction and interseasonal movement of rainfall band.
Since the meridional positions of the east and west part of Western Pacific Subtropical High (WPSH) affect the climate over China differently, we re-defined the meridional index of WPSH in this study. The mean latitude of the location of 500 hPa geopotential height maximum along several meridian in 10°N-60°N, 110°E-130°E and 10°N-60°N, 130°E-150°E is defined as new west index (Index_NEW_west) and new east index (Index_NEW_east), respectively. Their average value is defined as new meridional index of WPSH (Index_NEW). The correlation between the indices and summer precipitation over eastern China is more significant than the ridge index defined by National Climate Center (Index_NCC), specifically for the positive correlation between Index_NEW_west and precipitation over North China plain. The negative correlation between Index_NEW_east and precipitation over Yangtze River basin is similar to that of Index_NCC. Regression of the 500 hPa horizontal wind with respect to Index_NEW_west (Index_NEW_east) presents anticyclonic circulation over western North Pacific and the anticyclone center locates near 38°N,130°E (40°N,145°E). The various collocations between north/south anomalies of Index_NEW_west/Index_NEW_east correspond to four types of rainfall patterns. The good relationship between the interannual variation of new indices and summer precipitation over eastern China provides more valuable reference for the study of precipitation prediction and interseasonal movement of rainfall band.
Abstract:
In the summer of 2020, the precipitation in Chongqing was the fourth most since the same period with meteorological records. During the period, with heavy rain and strong intensity, the precipitation was extremely abnormal.This paper uses the daily precipitation data from 1961 to 2020, daily height field, wind field, water vapor field and sea temperature field of 34 stations in Chongqing, and uses relevant and main component analysis to analyze the main reasons for the abnormal deviation and abnormal changes in summer precipitation in Chongqing in 2020.The analysis shows that in the summer of 2020, the atmospheric circulation in the
In the summer of 2020, the precipitation in Chongqing was the fourth most since the same period with meteorological records. During the period, with heavy rain and strong intensity, the precipitation was extremely abnormal.This paper uses the daily precipitation data from 1961 to 2020, daily height field, wind field, water vapor field and sea temperature field of 34 stations in Chongqing, and uses relevant and main component analysis to analyze the main reasons for the abnormal deviation and abnormal changes in summer precipitation in Chongqing in 2020.The analysis shows that in the summer of 2020, the atmospheric circulation in the
Abstract:
The mesoscale characteristics of a local short-time severe convective rainstorm that occurred at the eastern foot of Helan Mountains in August Ningxia in 2019 were analyzed based on the data from H8 satellite, Doppler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that: (1) The southerly jet of 700 hPa that established 6 hours before the rainstorm and strengthened at night not only contributed to high temperature, high humidity, and the enhancement of atmospheric instability and dynamic and thermal uplift mechanisms in the lower layers of the rainstorm area, but also helped mesoscale ground convergence line to trigger the meso-β scale convective system in the eastern slope of Helan Mountains and strengthen it to meso-α scale convective system, leading to the generation and development of the severe convective rainstorm eventually. (2) The rainstorm occurred in the front-left of jet axis of 700 hPa, the high humidity area with water vapor flux ≥6 g?cm-1?s-1?hPa-1 of 700 hPa and specific humidity ≥12 g?kg-1 of 850 hPa, the high energy area with convective available potential energy ≥1500 J?kg-1, the high temperature area with θse ≥346 K of 850 hPa, the vertical upwarding area with centric intensity ≤-1.2 Pa?s-1 of 800 hPa, and the front of cold cloud where the large gradient (G) of cloud top brightness temperature (TBB) occurred. (3) During the strongest rainfall period, the jet axis was closest to the rainstorm area, the TBB ≤-66 ℃, the G ≥27 ℃?km-1, the radar composite reflectivity (Z) ≥65 dBZ, the echo tops (H ) ≥10 km, the vertical integrated liquid water (VIL) ≥11 kg?m-2, and the area of the cold cloud below -52 ℃ was about 1/5 of mesoscale convective complex. (4) The lower TBB was and the higher G and cooling rate (CR) were, the greater intensity of precipitation would be. The minimum TBB, the maximum G, the leap of Z and VIL, and the increase of echo height appeared 10~20 minutes earlier than the maximum rainfall, and the mesoscale ground convergence line appeared 30 minutes earlier than the rainfall.
The mesoscale characteristics of a local short-time severe convective rainstorm that occurred at the eastern foot of Helan Mountains in August Ningxia in 2019 were analyzed based on the data from H8 satellite, Doppler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that: (1) The southerly jet of 700 hPa that established 6 hours before the rainstorm and strengthened at night not only contributed to high temperature, high humidity, and the enhancement of atmospheric instability and dynamic and thermal uplift mechanisms in the lower layers of the rainstorm area, but also helped mesoscale ground convergence line to trigger the meso-β scale convective system in the eastern slope of Helan Mountains and strengthen it to meso-α scale convective system, leading to the generation and development of the severe convective rainstorm eventually. (2) The rainstorm occurred in the front-left of jet axis of 700 hPa, the high humidity area with water vapor flux ≥6 g?cm-1?s-1?hPa-1 of 700 hPa and specific humidity ≥12 g?kg-1 of 850 hPa, the high energy area with convective available potential energy ≥1500 J?kg-1, the high temperature area with θse ≥346 K of 850 hPa, the vertical upwarding area with centric intensity ≤-1.2 Pa?s-1 of 800 hPa, and the front of cold cloud where the large gradient (G) of cloud top brightness temperature (TBB) occurred. (3) During the strongest rainfall period, the jet axis was closest to the rainstorm area, the TBB ≤-66 ℃, the G ≥27 ℃?km-1, the radar composite reflectivity (Z) ≥65 dBZ, the echo tops (H ) ≥10 km, the vertical integrated liquid water (VIL) ≥11 kg?m-2, and the area of the cold cloud below -52 ℃ was about 1/5 of mesoscale convective complex. (4) The lower TBB was and the higher G and cooling rate (CR) were, the greater intensity of precipitation would be. The minimum TBB, the maximum G, the leap of Z and VIL, and the increase of echo height appeared 10~20 minutes earlier than the maximum rainfall, and the mesoscale ground convergence line appeared 30 minutes earlier than the rainfall.
Select AllDeselectExport
Display Method:
2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
Abstract:
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
Abstract:
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Zhou Yuquan, Chen Yingying, Li Juan, Huang Yimei, He Xiaodong, Zhou Feifei, Wu Menxin, Hu Bo, Mao Jietai
2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
Abstract:
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
Abstract:
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
Abstract:
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
Abstract:
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
Abstract:
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
FU Jiaolan, MA Xuekuan, CHEN Tao, ZHANG Fang, ZHANG Xidi, SUN Jun, QUAN Wanqing, YANG Shunan, SHEN Xiaolin
2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
Abstract:
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
Abstract:
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.1.001
Abstract:
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
Abstract:
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
Abstract:
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
Abstract:
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
Abstract:
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
Abstract:
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
Abstract:
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
2013,39(3):281-290, DOI: 10.7519/j.issn.1000-0526.2013.03.002
Abstract:
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
2011,37(2):142-155, DOI: 10.7519/j.issn.1000-0526.2011.2.003
Abstract:
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
Mobile website
® 2022 All Rights Reserved
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
ISSN:1000-0526 CN:11-2282/P