ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,2024 Issue 6
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- The Future Projections of Extreme Weather, Climate and Water Events and Strategic Responses
- A Review of Downburst Genesis Mechanism and Warning
- The Pattern Structure and Thermodynamic and Dynamic Processes of Severe Storms Associated with Linear Convective Gales
- Analysis on Extremity and Characteristics of the “21·7” Severe Torrential Rain in Henan Province
- Diagnostic Analysis on Water Vapor and Jet Characteristics of the July 2021 Severe Torrential Rain in Henan Province
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2024,50(6):649-660, DOI: 10.7519/j.issn.1000-0526.2024.031402
Abstract:
In this paper, the performance of the forecasting system of short-term multi-category convective phenomena in the event that happened on 13 June 2022 is analyzed first. Then, based on the objective probability forecasts of thunderstorm, short-time severe rainfall, thunderstorm gale and hail events in 2022 as well as available multi-category severe convective monitoring data, the performance of objective probability forecast products of the four types of severe convective weather provided by the short-term forecasting system is evaluated in detail by adopting the spatial test methods used in the severe convection forecast operations and the indices that indicate deterministic and probabilistic properties. The evaluated forecast period of the forecast products initiated at 08:00 BT from 1 April to 30 September 2022 is 96 h with interval of 12 h. Case studies show that the potential area of the four different convective phenomena could be well forecasted 24 h in advance. Statistical verification results show that the short-time severe rainfall forecast has the best performance among the four convective weather phenomena, followed by the forecast of thunderstorm. The forecast of the thunderstorm gale has certain applicability as well. There are obvious problems of overestimation in all the four convective weather phenomena compared to the observations. The diurnal variations of thunderstorm, short-time severe rainfall and thunderstorm gale forecasts are related to the forecast coverage time. These evaluation results are beneficial to subsequent improvement and development of forecast model and system, and could provide a useful reference for the operational application of multi-category severe convection forecast results based on the fusion of physical understanding and fuzzy logic artificial intelligence.
In this paper, the performance of the forecasting system of short-term multi-category convective phenomena in the event that happened on 13 June 2022 is analyzed first. Then, based on the objective probability forecasts of thunderstorm, short-time severe rainfall, thunderstorm gale and hail events in 2022 as well as available multi-category severe convective monitoring data, the performance of objective probability forecast products of the four types of severe convective weather provided by the short-term forecasting system is evaluated in detail by adopting the spatial test methods used in the severe convection forecast operations and the indices that indicate deterministic and probabilistic properties. The evaluated forecast period of the forecast products initiated at 08:00 BT from 1 April to 30 September 2022 is 96 h with interval of 12 h. Case studies show that the potential area of the four different convective phenomena could be well forecasted 24 h in advance. Statistical verification results show that the short-time severe rainfall forecast has the best performance among the four convective weather phenomena, followed by the forecast of thunderstorm. The forecast of the thunderstorm gale has certain applicability as well. There are obvious problems of overestimation in all the four convective weather phenomena compared to the observations. The diurnal variations of thunderstorm, short-time severe rainfall and thunderstorm gale forecasts are related to the forecast coverage time. These evaluation results are beneficial to subsequent improvement and development of forecast model and system, and could provide a useful reference for the operational application of multi-category severe convection forecast results based on the fusion of physical understanding and fuzzy logic artificial intelligence.
2024,50(6):661-674, DOI: 10.7519/j.issn.1000-0526.2024.032601
Abstract:
Using the FY-4A satellite water vapor images and geostationary interferometric infrared sounder (GIIRS) products combined with potential vorticity products, the cold wave in central and eastern China from 6 to 8 January in 2021 is analyzed, based on the interpretation principle of meteorological satellite images and basic theory of potential vorticity conservation. It is found that this cold wave event was affected mainly by the high-altitude cold vortex and the surface cold high. The low-level cold air moved from the south of Baikal Lake to southeast and strengthened at 08:00 BT 5 January. By 20:00 BT 8, it weakened. The comparison of 850 hPa 24 h temperature changes of FY-4A/GIIRS and ERA5 shows that the characteristics of the low troposphere cold air moving to southeast and the cold and warm temperature change regional distribution monitored by FY-4A/GIIRS are basically consistent with the ERA5 data. The 24 h negative temperature change center at 850 hPa and the location of 0℃ isallotherm by FY-4A/GIIRS were similar to the ERA5 data. The intensity of the 24 h temperature change center at 850 hPa by FY-4A/GIIRS was slightly higher than that of ERA5. The increase of high-level potential vorticity near the enhancement of the dark area of the water vapor image triggered the enhancement of the subsidence movement behind the high-level cyclonic circulation, and the dry air subsidence caused the enhancement of the surface high pressure. The increase of absolute vorticity near the center of 500 hPa cold vortex was one of the reasons for the enhancement of cold air. During the period of sharp strengthening of cold air, the increase of vortices in the middle and lower layers resulted in the accumulation of cold air on the ground and the enhancement of cold wave. The analysis result of potential vorticity theory on the enhancement mechanism of cold air is consistent with the development characteristic of cold wave movement of FY-4A/GIIRS temperature data. This indicates that the application of FY-4A/GIIRS temperature data can be effectively used to analyze the evolution characteristics of cold wave.
Using the FY-4A satellite water vapor images and geostationary interferometric infrared sounder (GIIRS) products combined with potential vorticity products, the cold wave in central and eastern China from 6 to 8 January in 2021 is analyzed, based on the interpretation principle of meteorological satellite images and basic theory of potential vorticity conservation. It is found that this cold wave event was affected mainly by the high-altitude cold vortex and the surface cold high. The low-level cold air moved from the south of Baikal Lake to southeast and strengthened at 08:00 BT 5 January. By 20:00 BT 8, it weakened. The comparison of 850 hPa 24 h temperature changes of FY-4A/GIIRS and ERA5 shows that the characteristics of the low troposphere cold air moving to southeast and the cold and warm temperature change regional distribution monitored by FY-4A/GIIRS are basically consistent with the ERA5 data. The 24 h negative temperature change center at 850 hPa and the location of 0℃ isallotherm by FY-4A/GIIRS were similar to the ERA5 data. The intensity of the 24 h temperature change center at 850 hPa by FY-4A/GIIRS was slightly higher than that of ERA5. The increase of high-level potential vorticity near the enhancement of the dark area of the water vapor image triggered the enhancement of the subsidence movement behind the high-level cyclonic circulation, and the dry air subsidence caused the enhancement of the surface high pressure. The increase of absolute vorticity near the center of 500 hPa cold vortex was one of the reasons for the enhancement of cold air. During the period of sharp strengthening of cold air, the increase of vortices in the middle and lower layers resulted in the accumulation of cold air on the ground and the enhancement of cold wave. The analysis result of potential vorticity theory on the enhancement mechanism of cold air is consistent with the development characteristic of cold wave movement of FY-4A/GIIRS temperature data. This indicates that the application of FY-4A/GIIRS temperature data can be effectively used to analyze the evolution characteristics of cold wave.
2024,50(6):675-685, DOI: 10.7519/j.issn.1000-0526.2024.022002
Abstract:
Using the basic reflectivity factor PPI image data of 47 severe convective cases from 50 S-band Doppler weather radars in the central-eastern region of China from 2016 to 2020, the three-body scatter spike (TBSS) characteristics are analyzed based on the screening of 2626 TBSS samples. The results show that TBSS is most frequently observed at altitudes of 1.5 km and 5 km and at the elevation 2.4°. TBSS is mainly observed in the range from the edge of the radar static cone area to the radar radial distance of 210 km. It reaches its peak at the spot 115 km away from the radar. In the radar polar coordinate system, TBSS appears more in the south than in the north, and more in the west than in the east. It is better to observe TBSS when the angle between the moving direction of the convective storm and the radial direction of the radar is larger than 30°. The TBSS echo strength decreases rapidly to 5 dBz within 0-15 km radially outward from the beginning, and fluctuates in the range of -5 and 10 dBz after 15 km, with more than 70% of the TBSS zone being weak echoes weaker than 25 dBz. 99% of TBSS length is under 40 km, and the patterns of TBSSs with varying lengths follow a normal distribution. No significant correlation is found between the frequency and length of TBSS occurrences and the highest value of the high echo core and the area of the high echo.
Using the basic reflectivity factor PPI image data of 47 severe convective cases from 50 S-band Doppler weather radars in the central-eastern region of China from 2016 to 2020, the three-body scatter spike (TBSS) characteristics are analyzed based on the screening of 2626 TBSS samples. The results show that TBSS is most frequently observed at altitudes of 1.5 km and 5 km and at the elevation 2.4°. TBSS is mainly observed in the range from the edge of the radar static cone area to the radar radial distance of 210 km. It reaches its peak at the spot 115 km away from the radar. In the radar polar coordinate system, TBSS appears more in the south than in the north, and more in the west than in the east. It is better to observe TBSS when the angle between the moving direction of the convective storm and the radial direction of the radar is larger than 30°. The TBSS echo strength decreases rapidly to 5 dBz within 0-15 km radially outward from the beginning, and fluctuates in the range of -5 and 10 dBz after 15 km, with more than 70% of the TBSS zone being weak echoes weaker than 25 dBz. 99% of TBSS length is under 40 km, and the patterns of TBSSs with varying lengths follow a normal distribution. No significant correlation is found between the frequency and length of TBSS occurrences and the highest value of the high echo core and the area of the high echo.
2024,50(6):686-700, DOI: 10.7519/j.issn.1000-0526.2024.033001
Abstract:
Using the detection results of Global Precipitation Measurement (GPM) dual-frequency precipitation radar (DPR) and microwave imager (GMI) from 2014 to 2021, the differences in observing snowfall processes between different precipitation products of DPR are compared. Moreover, the macro and micro characteristics of three types of snowfall systems (deep, shallow, and near surface) are clarified, and the structural characteristics of four typical snowfall clouds in Xinjiang are analyzed by means of equal frequency height statistical method. The results show that the probability of shallow snowfall clouds exceeds 60%, while deep snowfall clouds contribute the most to snowfall. The liquid water path (LWP) and ice water path (IWP) of the three types of clouds are mostly distributed in 80-450 g·m-2 and 100-380 g·m-2, with a positive correlation between the echo top height, LWP, and IWP and the near-surface snowfall rate as a whole. The four selected cases are located in the Ale Mount Taishan area (A), the Ili River Valley (B), the hinterland of the Gurban Tunggut Desert (C), and the northern foot of the Kunlun Mountains in southern Xinjiang (D).The snow system observation results of GMI’s 166 GHz high-frequency channel are more detailed, 〖JP2〗and the brightness temperature is concentrated in the range of 200-275 K.〖JP〗 Cases A and B are mainly ice clouds, and cases C and D are mostly ice water mixed clouds, and the snowfall intensity and area of the former are greater than the latter. The radar reflectivity factor (Z) of the cloud profile is concentrated in 16-25 dBz and 0.75-4.65 km height. Cloud clusters in cases A, B, and D exhibit a “left leaning” structure, with the highest echo intensity in the upper and middle parts of the cloud, belonging to a typical development stage of cloud cluster. The echo intensity of case C is mainly located in the lower part of the cloud, and the cloud cluster is in the mature stage. Dm (mass weighted average diameter) and dBNw (particle number concentration) produce more snowfall between 1.00-1.22 mm and 33-35, respectively. The snowfall intensity is not only related to the particle size of ice crystals or supercooled water, but also affected by the particle number concentration. This study is of significance for improving the level of snow monitoring in Xinjiang, understanding the formation mechanism of snowfall and evaluating the potential and effectiveness of artificial snow seeding and cloud seeding in different regions of northern and southern Xinjiang.
Using the detection results of Global Precipitation Measurement (GPM) dual-frequency precipitation radar (DPR) and microwave imager (GMI) from 2014 to 2021, the differences in observing snowfall processes between different precipitation products of DPR are compared. Moreover, the macro and micro characteristics of three types of snowfall systems (deep, shallow, and near surface) are clarified, and the structural characteristics of four typical snowfall clouds in Xinjiang are analyzed by means of equal frequency height statistical method. The results show that the probability of shallow snowfall clouds exceeds 60%, while deep snowfall clouds contribute the most to snowfall. The liquid water path (LWP) and ice water path (IWP) of the three types of clouds are mostly distributed in 80-450 g·m-2 and 100-380 g·m-2, with a positive correlation between the echo top height, LWP, and IWP and the near-surface snowfall rate as a whole. The four selected cases are located in the Ale Mount Taishan area (A), the Ili River Valley (B), the hinterland of the Gurban Tunggut Desert (C), and the northern foot of the Kunlun Mountains in southern Xinjiang (D).The snow system observation results of GMI’s 166 GHz high-frequency channel are more detailed, 〖JP2〗and the brightness temperature is concentrated in the range of 200-275 K.〖JP〗 Cases A and B are mainly ice clouds, and cases C and D are mostly ice water mixed clouds, and the snowfall intensity and area of the former are greater than the latter. The radar reflectivity factor (Z) of the cloud profile is concentrated in 16-25 dBz and 0.75-4.65 km height. Cloud clusters in cases A, B, and D exhibit a “left leaning” structure, with the highest echo intensity in the upper and middle parts of the cloud, belonging to a typical development stage of cloud cluster. The echo intensity of case C is mainly located in the lower part of the cloud, and the cloud cluster is in the mature stage. Dm (mass weighted average diameter) and dBNw (particle number concentration) produce more snowfall between 1.00-1.22 mm and 33-35, respectively. The snowfall intensity is not only related to the particle size of ice crystals or supercooled water, but also affected by the particle number concentration. This study is of significance for improving the level of snow monitoring in Xinjiang, understanding the formation mechanism of snowfall and evaluating the potential and effectiveness of artificial snow seeding and cloud seeding in different regions of northern and southern Xinjiang.
2024,50(6):701-710, DOI: 10.7519/j.issn.1000-0526.2024.020201
Abstract:
In order to improve the understanding of precipitation characteristics of hailstorm in the Tibetan Plateau, based on the raindrop size distribution data observed by DSG5 disdrometer, radar reflectivity, FY-4A satellite and minutely precipitation data, etc., the precipitation microphysical characteristics of the hailstorm that occurred in Lhasa on 23 July 2020 is analyzed. The results show that there were some slightly differences at the time of beginning and end of the hailstorm, precipitation peak and total precipitation between rain gauge and DSG5 disdrometer although the minutely precipitation amounts of the two were similar. The fitted curves of the average spectrum distribution of raindrops and hailstones were monotonously decreasing. The raindrop size spectrum conformed to Γ distribution and the hail size spectrum accorded with M-P distribution. In the early stage of hail process, the precipitation particles were mostly small, which was mainly caused by the evaporation of the raindrops. In the later stage, the spectral width of precipitation particles became wider, the collision and fragmentation of the particles and the melting of graupel particles produced a large number of small raindrops, leading to a sharp increase in the number of particle concentration. The significant increase of number concentration and the widening of the droplet spectrum in this stage were the reason for the increased rainfall. The number concentration of hailstones only accounted for 1.6% of the total number concentration of precipitation particles, while the hailstones were the major contributors of the surface total precipitation. The empirical formula for the average terminal falling velocity and the diameter of the hails was fitted based on the observation.
In order to improve the understanding of precipitation characteristics of hailstorm in the Tibetan Plateau, based on the raindrop size distribution data observed by DSG5 disdrometer, radar reflectivity, FY-4A satellite and minutely precipitation data, etc., the precipitation microphysical characteristics of the hailstorm that occurred in Lhasa on 23 July 2020 is analyzed. The results show that there were some slightly differences at the time of beginning and end of the hailstorm, precipitation peak and total precipitation between rain gauge and DSG5 disdrometer although the minutely precipitation amounts of the two were similar. The fitted curves of the average spectrum distribution of raindrops and hailstones were monotonously decreasing. The raindrop size spectrum conformed to Γ distribution and the hail size spectrum accorded with M-P distribution. In the early stage of hail process, the precipitation particles were mostly small, which was mainly caused by the evaporation of the raindrops. In the later stage, the spectral width of precipitation particles became wider, the collision and fragmentation of the particles and the melting of graupel particles produced a large number of small raindrops, leading to a sharp increase in the number of particle concentration. The significant increase of number concentration and the widening of the droplet spectrum in this stage were the reason for the increased rainfall. The number concentration of hailstones only accounted for 1.6% of the total number concentration of precipitation particles, while the hailstones were the major contributors of the surface total precipitation. The empirical formula for the average terminal falling velocity and the diameter of the hails was fitted based on the observation.
2024,50(6):711-722, DOI: 10.7519/j.issn.1000-0526.2023.092001
Abstract:
Based on observations and the 24 h mid-low level wind speed and temperature forecast data from the ECMWF deterministic model in the period of January to December 2021, a support vector machine regression method was employed to develop a gust forecast model for the offshore areas of China so as to enhance the capability of predicting gusts at sea. Independent sample verification was conducted using data from January to September 2022, and a comparative analysis was performed against the gust factor method. The following conclusions were drawn. Changes in wind speed and temperature at different heights or vertical wind speed and temperature variations can all have an impact on gust forecasts. Consequently, relying solely on the 10 m wind speed forecast from the model, as done in the gust factor method, may lead to overestimation or underestimation of gusts in certain situations. The forecast model that incorporates upper-level meteorological elements based on the gust factor method can achieve better forecast performance. For gust of scale 9, the accuracy of this model is 50%, significantly higher than the 30% accuracy of the gust factor method. It also demonstrates good performance for gusts of large scales in different sea areas. When there is a certain deviation between the 10 m wind speed forecast from the ECMWF deterministic model and the observed wind speed, the gust forecast results of the support vector machine regression model, which considers upper-level element information, are closer to the observation compared to the result by the gust factor method.
Based on observations and the 24 h mid-low level wind speed and temperature forecast data from the ECMWF deterministic model in the period of January to December 2021, a support vector machine regression method was employed to develop a gust forecast model for the offshore areas of China so as to enhance the capability of predicting gusts at sea. Independent sample verification was conducted using data from January to September 2022, and a comparative analysis was performed against the gust factor method. The following conclusions were drawn. Changes in wind speed and temperature at different heights or vertical wind speed and temperature variations can all have an impact on gust forecasts. Consequently, relying solely on the 10 m wind speed forecast from the model, as done in the gust factor method, may lead to overestimation or underestimation of gusts in certain situations. The forecast model that incorporates upper-level meteorological elements based on the gust factor method can achieve better forecast performance. For gust of scale 9, the accuracy of this model is 50%, significantly higher than the 30% accuracy of the gust factor method. It also demonstrates good performance for gusts of large scales in different sea areas. When there is a certain deviation between the 10 m wind speed forecast from the ECMWF deterministic model and the observed wind speed, the gust forecast results of the support vector machine regression model, which considers upper-level element information, are closer to the observation compared to the result by the gust factor method.
2024,50(6):723-732, DOI: 10.7519/j.issn.1000-0526.2024.031901
Abstract:
Addressing the limitations of traditional models in capturing long-term dependencies and generalization ability in meteorological sequences, we propose a novel air temperature forecasting model based on sparse attention and adaptive seasonal and trend decomposition using loess (ATFSAS) in this paper. ATFSAS employs an encoder-decoder architecture, and integrates a sparse attention mechanism to effectively capture long-term dependencies in meteorological observation data. An information distillation method is introduced to reduce redundancy during the encoding process. The model refines the periodic and trend components in the forecast signals by combining a multi-layer decoder with an adaptive timing decomposition unit, achieving precise air temperature forecast. Based on the climate dataset in Jena, Germany, 24 h refined air temperature forecast is performed by ATFSAS, abtaining a mean absolute error of 1.7108℃. Compared to the LSTM model, ATFSAS demonstrates superior performance in medium-short term daily average air temperature and multi-region single-day average air temperature forecasts based on the China ground climate daily dataset, and their mean absolute errors get improved by 35.56% and 23.66%, respectively.
Addressing the limitations of traditional models in capturing long-term dependencies and generalization ability in meteorological sequences, we propose a novel air temperature forecasting model based on sparse attention and adaptive seasonal and trend decomposition using loess (ATFSAS) in this paper. ATFSAS employs an encoder-decoder architecture, and integrates a sparse attention mechanism to effectively capture long-term dependencies in meteorological observation data. An information distillation method is introduced to reduce redundancy during the encoding process. The model refines the periodic and trend components in the forecast signals by combining a multi-layer decoder with an adaptive timing decomposition unit, achieving precise air temperature forecast. Based on the climate dataset in Jena, Germany, 24 h refined air temperature forecast is performed by ATFSAS, abtaining a mean absolute error of 1.7108℃. Compared to the LSTM model, ATFSAS demonstrates superior performance in medium-short term daily average air temperature and multi-region single-day average air temperature forecasts based on the China ground climate daily dataset, and their mean absolute errors get improved by 35.56% and 23.66%, respectively.
2024,50(6):733-745, DOI: 10.7519/j.issn.1000-0526.2024.041701
Abstract:
In order to analyze the distribution characteristics of ice crystals in cold clouds and reveal the evolution mechanism of their growth, ice crystals are classified into 8 categories and labeled according to their shapes and sizes. At the same time, one type of partition column is labeled for data quality control. Then, the 9 types of labeled images are integrated to build an image dataset. The transfer learning VGGNet16 model is adopted for identification training, and the classification accuracy of the trained model reaches 98%. The model is applied to the study of ice crystal characteristics of cold clouds in autumn. Three cumulus-stratiform mixed cloud precipitation processes and three stratiform cloud precipitation processes in 2019 are selected to analyze the proportion of ice crystal shapes in different temperature ranges and the change characteristics of ice crystal size distribution. The results show that the initial shape distribution of ice crystal is determined by the temperature’s affecting the ratio of base surface to edge surface of ice crystals. In the same temperature range, the proportion of spherical ice crystals and linear ice crystals in cumulus-stratiform mixed clouds is higher than that in stratiform cloud, and the proportion of various ice crystals is relatively fixed when the temperature is below -12℃. In cumulus-stratiform mixed clouds, the diameters of linear ice crystals are concentrated in 300-800 μm with the ice crystal size distribution being multimodal. The diameters of aggregated ice crystals are greater than 600 μm. The concentrations at the beginning and the end of the ice crystal spectrum are equal. The diameters of spherical ice crystals are concentrated in the range of 120-300 μm, and the ice crystal size distribution shows a monotonically decreasing trend.
In order to analyze the distribution characteristics of ice crystals in cold clouds and reveal the evolution mechanism of their growth, ice crystals are classified into 8 categories and labeled according to their shapes and sizes. At the same time, one type of partition column is labeled for data quality control. Then, the 9 types of labeled images are integrated to build an image dataset. The transfer learning VGGNet16 model is adopted for identification training, and the classification accuracy of the trained model reaches 98%. The model is applied to the study of ice crystal characteristics of cold clouds in autumn. Three cumulus-stratiform mixed cloud precipitation processes and three stratiform cloud precipitation processes in 2019 are selected to analyze the proportion of ice crystal shapes in different temperature ranges and the change characteristics of ice crystal size distribution. The results show that the initial shape distribution of ice crystal is determined by the temperature’s affecting the ratio of base surface to edge surface of ice crystals. In the same temperature range, the proportion of spherical ice crystals and linear ice crystals in cumulus-stratiform mixed clouds is higher than that in stratiform cloud, and the proportion of various ice crystals is relatively fixed when the temperature is below -12℃. In cumulus-stratiform mixed clouds, the diameters of linear ice crystals are concentrated in 300-800 μm with the ice crystal size distribution being multimodal. The diameters of aggregated ice crystals are greater than 600 μm. The concentrations at the beginning and the end of the ice crystal spectrum are equal. The diameters of spherical ice crystals are concentrated in the range of 120-300 μm, and the ice crystal size distribution shows a monotonically decreasing trend.
2024,50(6):746-755, DOI: 10.7519/j.issn.1000-0526.2024.030401
Abstract:
In view of the difficulties in monitoring summer rainy season in North China, the concept of the summer potential rainy season in North China is proposed, and a new monitoring method， i.e., the speci-fic humidity subtropical high method, is established. The main monitoring results are as follows. The average start date of the summer rainy season in North China from 1961 to 2022 is 10 July, the end date is 8 August, and the rainy season lasts for 28 days. The start and end time of the rainy season in North China has no obvious long-term change trend, but the interdecadal change is significant. The summer rainy season precipitation and the comprehensive intensity index of rainy season monitored by this method in North China are very consistent with the changes in summer precipitation, which is a high positive correlation. This indicates that the monitored rainy season parameters have a good indication of the changes in summer precipitation in North China. The start and end of the summer rainy season in North China are accompanied by significant changes in atmospheric circulation. The East Asian subtropical summer monsoon at 850 hPa strengthens and weakens, and the atmospheric specific humidity in North China north of 30°N rapidly increases and decreases. The 500 hPa height field presents positive and negative anomaly centers in North China, and the Northwest Pacific subtropical high begins to significantly lift northward or retreat eastward along the coast of East Asia. The upper westerly jet axis at 200 hPa moves north from 37.5°N to 41.5°N or south from 44.5°N to 40.5°N.
In view of the difficulties in monitoring summer rainy season in North China, the concept of the summer potential rainy season in North China is proposed, and a new monitoring method， i.e., the speci-fic humidity subtropical high method, is established. The main monitoring results are as follows. The average start date of the summer rainy season in North China from 1961 to 2022 is 10 July, the end date is 8 August, and the rainy season lasts for 28 days. The start and end time of the rainy season in North China has no obvious long-term change trend, but the interdecadal change is significant. The summer rainy season precipitation and the comprehensive intensity index of rainy season monitored by this method in North China are very consistent with the changes in summer precipitation, which is a high positive correlation. This indicates that the monitored rainy season parameters have a good indication of the changes in summer precipitation in North China. The start and end of the summer rainy season in North China are accompanied by significant changes in atmospheric circulation. The East Asian subtropical summer monsoon at 850 hPa strengthens and weakens, and the atmospheric specific humidity in North China north of 30°N rapidly increases and decreases. The 500 hPa height field presents positive and negative anomaly centers in North China, and the Northwest Pacific subtropical high begins to significantly lift northward or retreat eastward along the coast of East Asia. The upper westerly jet axis at 200 hPa moves north from 37.5°N to 41.5°N or south from 44.5°N to 40.5°N.
2024,50(6):756-769, DOI: 10.7519/j.issn.1000-0526.2024.040802
Abstract:
In order to determine the sections with potential wind disasters along the high-speed railway and reduce the occurrence of floating objects invasion disasters caused by strong winds, based on the observation data of meteorological stations along the high-speed railway in Tianjin, high-resolution series of satellite remote sensing image data, historical disaster of high-speed railway and basic geographic information, this article analyzes the impact of strong wind on the invasion disaster of light floating objects and proposes the wind speed threshold range and dominant wind direction of disasters in different regional sections of the Tianjin High-Speed Railway. Then, based the risk assessment theory of natural disasters, the meteorological risk analysis model of the wind-induced light floating objects invasion disaster of high-speed railway is established, and the risk zoning is formed. The results show that the invasion disasters of light floating objects along the high-speed railway mainly occur in spring and winter, accounting for 73.75% of the total invasion disasters of the whole year. The most concentrated occurrence time is from 12:00 BT to 15:00 BT in the afternoon, with most seen in the central and eastern parts of Tianjin and then in the northwestern and the southwestern parts in order. Disasters mainly occur in the wind speed range with the maximum wind speed of 8-17 m·s-1 and extreme wind speed of 13-21 m·s-1. When the wind direction is from west to north and the wind direction is at the angle of more than 45 ° with the line, disasters are more likely to occur. By means of satellite remote sensing technology, the distribution of hidden dangers along the Tianjin High-Speed Railway could be well identified, and the highest identification accuracy could reach 72.7%. Based on the characteristics of wind speed and wind direction and the distribution of hidden dangers, the meteorological risk analysis model of the Tianjin High-Speed Railway wind disaster is established, and the zoning results show that the Beijing-Shanghai High-Speed Railway and the Beijing-Tianjin Intercity Railway have higher risks, followed by the Tianjin-Qinhuangdao High-Speed Railway, and the Tianjin-Bazhou Passenger Dedicated-Line has the lowest risk. High risk sections are mainly concentrated in first, the north of the Wuqing District, Beichen District and Xiqing District of the Beijing-Shanghai High-Speed Railway, second, the Beichen District, the east of the Dongli District and the Binhai New Area section of the Beijing-Tianjin Intercity, and third, the east of the Dongli District of the Tianjin-Qinhuangdao High-Speed Railway.
In order to determine the sections with potential wind disasters along the high-speed railway and reduce the occurrence of floating objects invasion disasters caused by strong winds, based on the observation data of meteorological stations along the high-speed railway in Tianjin, high-resolution series of satellite remote sensing image data, historical disaster of high-speed railway and basic geographic information, this article analyzes the impact of strong wind on the invasion disaster of light floating objects and proposes the wind speed threshold range and dominant wind direction of disasters in different regional sections of the Tianjin High-Speed Railway. Then, based the risk assessment theory of natural disasters, the meteorological risk analysis model of the wind-induced light floating objects invasion disaster of high-speed railway is established, and the risk zoning is formed. The results show that the invasion disasters of light floating objects along the high-speed railway mainly occur in spring and winter, accounting for 73.75% of the total invasion disasters of the whole year. The most concentrated occurrence time is from 12:00 BT to 15:00 BT in the afternoon, with most seen in the central and eastern parts of Tianjin and then in the northwestern and the southwestern parts in order. Disasters mainly occur in the wind speed range with the maximum wind speed of 8-17 m·s-1 and extreme wind speed of 13-21 m·s-1. When the wind direction is from west to north and the wind direction is at the angle of more than 45 ° with the line, disasters are more likely to occur. By means of satellite remote sensing technology, the distribution of hidden dangers along the Tianjin High-Speed Railway could be well identified, and the highest identification accuracy could reach 72.7%. Based on the characteristics of wind speed and wind direction and the distribution of hidden dangers, the meteorological risk analysis model of the Tianjin High-Speed Railway wind disaster is established, and the zoning results show that the Beijing-Shanghai High-Speed Railway and the Beijing-Tianjin Intercity Railway have higher risks, followed by the Tianjin-Qinhuangdao High-Speed Railway, and the Tianjin-Bazhou Passenger Dedicated-Line has the lowest risk. High risk sections are mainly concentrated in first, the north of the Wuqing District, Beichen District and Xiqing District of the Beijing-Shanghai High-Speed Railway, second, the Beichen District, the east of the Dongli District and the Binhai New Area section of the Beijing-Tianjin Intercity, and third, the east of the Dongli District of the Tianjin-Qinhuangdao High-Speed Railway.
2024,50(6):770-776, DOI: 10.7519/j.issn.1000-0526.2024.051101
Abstract:
The main characteristics of the general atmospheric circulation in March 2024 are as follows. There was one polar vortex center in the Northern Hemisphere, which was stronger than usual. The circulation in mid-high latitudes showed an anomalous four-wave pattern, and the Asian circulation was relatively flat and straight. The northern part of China was basically in a negative anomaly zone of the 500 hPa geopotential height field. The strength of Western Pacific subtropical high was stronger and more westward than in normal years, while the south branch trough was a little weaker than usual. The monthly mean temperature was 6.0℃ across China, which is 1.2℃ warmer than normal. The monthly mean precipitation amount was 24.0 mm, 18.4% less than in normal period (29.4 mm). However，the precipitation in the north of Inner Mongolia and the east of Northwest China was significantly more than that in normal years. During this month, one large-scale precipitation process occurred, and severe convection weather appeared frequently with three regional convection events with strong localized intensities. In addition, there were two cold air processes without causing large range of drop in temperature. Three sand-dust weather processes occurred in northern China, and the drought condition continued in winter and spring in the southwestern region of China.
The main characteristics of the general atmospheric circulation in March 2024 are as follows. There was one polar vortex center in the Northern Hemisphere, which was stronger than usual. The circulation in mid-high latitudes showed an anomalous four-wave pattern, and the Asian circulation was relatively flat and straight. The northern part of China was basically in a negative anomaly zone of the 500 hPa geopotential height field. The strength of Western Pacific subtropical high was stronger and more westward than in normal years, while the south branch trough was a little weaker than usual. The monthly mean temperature was 6.0℃ across China, which is 1.2℃ warmer than normal. The monthly mean precipitation amount was 24.0 mm, 18.4% less than in normal period (29.4 mm). However，the precipitation in the north of Inner Mongolia and the east of Northwest China was significantly more than that in normal years. During this month, one large-scale precipitation process occurred, and severe convection weather appeared frequently with three regional convection events with strong localized intensities. In addition, there were two cold air processes without causing large range of drop in temperature. Three sand-dust weather processes occurred in northern China, and the drought condition continued in winter and spring in the southwestern region of China.
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Available online: June 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022003
Abstract:
Based on forecast products of the European Center for Medium-Range Weather Forecasts - Integrated Forecasting System(ECMWF-IFS) and hourly temperature observation data from the China Meteorological Administration Land Data Assimilation System(CLDAS), an enhanced model named ED-LSTM-FCNN is constructed, incorporating an embedding layer module to handle high-dimensional spatial and temporal features. A fully connected neural network was utilized to integrate various features types and achieve regression prediction of temperature, generating gridded hourly temperature forecast products with a resolution of 0.05°×0.05°. Verification for the 2022 forecast in Hunan Province revealed that the model exhibits a notable capacity to mitigate forecast errors inherent in the numerical model, thereby enhancing the overall forecast stability. The root mean square errors (RMSE) for forecast lead times ranging from 1 to 24 hours exhibit a reduction of 25.4% to 37.7% when compared to ECMWF-IFS and a decrease of 15.8% to 40.0% in comparison to the SCMOC. The model significantly enhances the forecast performance of ECMWF-IFS in spatial prediction, particularly in regions characterized by intricate terrain features. The RMSEs across most areas vary within the range of 1.2 ℃ to 1.6 ℃. The forecast accuracy of the model, with an error margin of ±2 ℃, surpasses 85.0% across various seasons, demonstrating a significant improvement compared to both ECMWF-IFS and SCMOC. The forecasting performance is notably superior, particularly in stable extreme high-temperature weather conditions, when compared to alternative products. In conclusion, this method proved to be effective for high-resolution temperature grid forecasting operations.
Based on forecast products of the European Center for Medium-Range Weather Forecasts - Integrated Forecasting System(ECMWF-IFS) and hourly temperature observation data from the China Meteorological Administration Land Data Assimilation System(CLDAS), an enhanced model named ED-LSTM-FCNN is constructed, incorporating an embedding layer module to handle high-dimensional spatial and temporal features. A fully connected neural network was utilized to integrate various features types and achieve regression prediction of temperature, generating gridded hourly temperature forecast products with a resolution of 0.05°×0.05°. Verification for the 2022 forecast in Hunan Province revealed that the model exhibits a notable capacity to mitigate forecast errors inherent in the numerical model, thereby enhancing the overall forecast stability. The root mean square errors (RMSE) for forecast lead times ranging from 1 to 24 hours exhibit a reduction of 25.4% to 37.7% when compared to ECMWF-IFS and a decrease of 15.8% to 40.0% in comparison to the SCMOC. The model significantly enhances the forecast performance of ECMWF-IFS in spatial prediction, particularly in regions characterized by intricate terrain features. The RMSEs across most areas vary within the range of 1.2 ℃ to 1.6 ℃. The forecast accuracy of the model, with an error margin of ±2 ℃, surpasses 85.0% across various seasons, demonstrating a significant improvement compared to both ECMWF-IFS and SCMOC. The forecasting performance is notably superior, particularly in stable extreme high-temperature weather conditions, when compared to alternative products. In conclusion, this method proved to be effective for high-resolution temperature grid forecasting operations.
Available online: June 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.042601
Abstract:
Based on the characteristics of simultaneous observation of cloud tops by ground-based millimeter-wave cloud radar and FY-4A satellite, the relationship between cloud top height observed by cloud radar and AGRI load channel data of FY-4A satellite was analyzed, and a joint inversion of cloud top height based on cloud radar and FY-4A Satellite is proposed. The cloud top height of the satellite in a certain area around the installation point of the cloud radar is retrieved, and the inversion results are verified and analyzed. The results show that the 11-14 channel DN value of FY-4A satellite is linearly correlated with the cloud top height of cloud radar. Moreover, the ratio of FY-4A satellite channel value to cloud top height observed by cloud radar shows the seasonal characteristics of minimum in winter, followed by spring and autumn, and maximum in summer. The correlation coefficient between cloud top height obtained from satellite-ground fusion inversion and cloud top height measured by cloud radar is 0.84, and the root-mean-square error decreases by 0.7km after fusion, which improves the inversion accuracy of satellite cloud top height.
Based on the characteristics of simultaneous observation of cloud tops by ground-based millimeter-wave cloud radar and FY-4A satellite, the relationship between cloud top height observed by cloud radar and AGRI load channel data of FY-4A satellite was analyzed, and a joint inversion of cloud top height based on cloud radar and FY-4A Satellite is proposed. The cloud top height of the satellite in a certain area around the installation point of the cloud radar is retrieved, and the inversion results are verified and analyzed. The results show that the 11-14 channel DN value of FY-4A satellite is linearly correlated with the cloud top height of cloud radar. Moreover, the ratio of FY-4A satellite channel value to cloud top height observed by cloud radar shows the seasonal characteristics of minimum in winter, followed by spring and autumn, and maximum in summer. The correlation coefficient between cloud top height obtained from satellite-ground fusion inversion and cloud top height measured by cloud radar is 0.84, and the root-mean-square error decreases by 0.7km after fusion, which improves the inversion accuracy of satellite cloud top height.
Available online: June 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.043001
Abstract:
One squall line influenced by Southwest Vortex occurred in the eastern Sichuan Basin from the night of June 4 to the day of June 5, 2019. Using multi-source observation data and ECMWF Reanalysis 5 (ERA5) data, the characteristic and formation of the squall line was analyzed. The results showed that convective heavy rainfall before occurrence of the squall line was formatted in the central Sichuan Basin under the background of the high-altitude trough and the warm Southwest Vortex, combined with troposphere atmospheric environment of the deep wet layer and certain convective available potential energy. The squall line occurred during the prominent frontogenesis process of cold front which surmounted the Qinling Mountains and entered the rear of the Southwest Vortex. With the joint influence of the high-altitude trough, the Southwest Vortex and the strong cold front, the cold front vertical circulation merged with the Southwest Vortex vertical circulation, and the combined vertical circulation circle significantly strengthened the uplift mechanism of the frontal zone. It provided favorable dynamic lifting conditions for the formation of the squall line in western Chongqing. The atmospheric environment in western Chongqing was conducive to the formation of the squall line, which had dry air in the middle troposphere, large vertical temperature lapse rate in the lower and middle troposphere layers, significant convective available potential energy, and large deep vertical wind shear. The formation process of the squall line on radar was characterized by the combined development of linear convection with the cold shear line and strong rainfall convection in the Southwest Vortex frontogenesis region, forming the "herringbone" echo in the west of Chongqing. The cold front behind the "herringbone" echo moved southward, combined with the evaporation and cooling of raindrops in the dry environment behind the front, cooled down the cold area formed by the rainstorm to the cold pool outflow in the boundary layer, which promoted the formation of the squall line. The arc-shaped squall line maintained for about 1.5 hours after the formation. The southward and downward transport of low-level horizontal kinetic energy at the rear of the front area and the enhancing of the potential temperature gradient between the ground cold and warm air during the formation of the squall line were all conducive to the formation of the ground gales.
One squall line influenced by Southwest Vortex occurred in the eastern Sichuan Basin from the night of June 4 to the day of June 5, 2019. Using multi-source observation data and ECMWF Reanalysis 5 (ERA5) data, the characteristic and formation of the squall line was analyzed. The results showed that convective heavy rainfall before occurrence of the squall line was formatted in the central Sichuan Basin under the background of the high-altitude trough and the warm Southwest Vortex, combined with troposphere atmospheric environment of the deep wet layer and certain convective available potential energy. The squall line occurred during the prominent frontogenesis process of cold front which surmounted the Qinling Mountains and entered the rear of the Southwest Vortex. With the joint influence of the high-altitude trough, the Southwest Vortex and the strong cold front, the cold front vertical circulation merged with the Southwest Vortex vertical circulation, and the combined vertical circulation circle significantly strengthened the uplift mechanism of the frontal zone. It provided favorable dynamic lifting conditions for the formation of the squall line in western Chongqing. The atmospheric environment in western Chongqing was conducive to the formation of the squall line, which had dry air in the middle troposphere, large vertical temperature lapse rate in the lower and middle troposphere layers, significant convective available potential energy, and large deep vertical wind shear. The formation process of the squall line on radar was characterized by the combined development of linear convection with the cold shear line and strong rainfall convection in the Southwest Vortex frontogenesis region, forming the "herringbone" echo in the west of Chongqing. The cold front behind the "herringbone" echo moved southward, combined with the evaporation and cooling of raindrops in the dry environment behind the front, cooled down the cold area formed by the rainstorm to the cold pool outflow in the boundary layer, which promoted the formation of the squall line. The arc-shaped squall line maintained for about 1.5 hours after the formation. The southward and downward transport of low-level horizontal kinetic energy at the rear of the front area and the enhancing of the potential temperature gradient between the ground cold and warm air during the formation of the squall line were all conducive to the formation of the ground gales.
Available online: June 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.040801
Abstract:
Based on the precipitation process of strong convective clouds in Xinjiang from 2015 to 2021 and the corresponding NPP/VIIRS satellite data, the microphysical characteristics of hail clouds and deep convective clouds were quantitatively analyzed by using the satellite cloud microphysical inversion technology, and the differences in the microphysical parameters of hail clouds in northern and southern Xinjiang were compared. The results show that:(1) the crystallization temperature of hail cloud (-34 ℃) is lower than that of deep convective cloud (-30.5 ℃), the height of deep convective cloud top is higher, and the hail cloud top has anvil structure; (2) Hail mostly occurs in June and July in northern Xinjiang, and mainly occurs in May and July in southern Xinjiang. Hail time is mainly distributed from 15:00-20:00. Hail in southern Xinjiang occurs in the early morning and early morning, accounting for more than that in northern Xinjiang; The mean duration of hail in northern and southern Xinjiang is 12.60 min and 12.27 min, and the mean maximum diameter of hail is 13.53 mm and 12.80 mm, respectively. The hail cloud top in northern Xinjiang is higher, the duration of hail is longer, the diameter of hail is larger, and the freezing temperature is lower than that in southern Xinjiang; (3) The mean cloud bottom temperature and cloud bottom height of hail in northern and southern Xinjiang are 5.15 ℃, 1.96 km and 4.85 ℃, 2.19 km respectively. The cloud bottom temperature in northern Xinjiang is warmer than that in southern Xinjiang, and the cloud bottom height is lower than that in southern Xinjiang; The rising speed of cloud base in South Xinjiang (2.07 m/s) is 1.13 times that in North Xinjiang (1.84 m/s), and the average thickness of hail cloud in North Xinjiang (8.90 km) is 1.25% greater than that in South Xinjiang (8.78 km); Influenced by human activities, industrial pollution and other factors, the mean concentration of condensation nuclei at the bottom of hail cloud in northern Xinjiang (396/cm3) is 65% higher than that in southern Xinjiang (240/cm3), which is dominated by agriculture. The mean maximum supersaturation of hail cloud bottom is 0.55% and 0.85% respectively. (4) Affected by the strong updraft, the growth time of hail cloud particles is short, and each growth zone develops slowly, and there is no rain embryo formation zone. Targeted seeding of hygroscopic nuclei in the middle and lower layers of the cloud in advance will promote the formation of precipitation at the bottom of the cloud as soon as possible, and excessive seeding of AgI ice nuclei near the 0 ℃ layer will compete for the supercooled water in the cloud, which can achieve the goal of increasing rain and preventing hail.
Based on the precipitation process of strong convective clouds in Xinjiang from 2015 to 2021 and the corresponding NPP/VIIRS satellite data, the microphysical characteristics of hail clouds and deep convective clouds were quantitatively analyzed by using the satellite cloud microphysical inversion technology, and the differences in the microphysical parameters of hail clouds in northern and southern Xinjiang were compared. The results show that:(1) the crystallization temperature of hail cloud (-34 ℃) is lower than that of deep convective cloud (-30.5 ℃), the height of deep convective cloud top is higher, and the hail cloud top has anvil structure; (2) Hail mostly occurs in June and July in northern Xinjiang, and mainly occurs in May and July in southern Xinjiang. Hail time is mainly distributed from 15:00-20:00. Hail in southern Xinjiang occurs in the early morning and early morning, accounting for more than that in northern Xinjiang; The mean duration of hail in northern and southern Xinjiang is 12.60 min and 12.27 min, and the mean maximum diameter of hail is 13.53 mm and 12.80 mm, respectively. The hail cloud top in northern Xinjiang is higher, the duration of hail is longer, the diameter of hail is larger, and the freezing temperature is lower than that in southern Xinjiang; (3) The mean cloud bottom temperature and cloud bottom height of hail in northern and southern Xinjiang are 5.15 ℃, 1.96 km and 4.85 ℃, 2.19 km respectively. The cloud bottom temperature in northern Xinjiang is warmer than that in southern Xinjiang, and the cloud bottom height is lower than that in southern Xinjiang; The rising speed of cloud base in South Xinjiang (2.07 m/s) is 1.13 times that in North Xinjiang (1.84 m/s), and the average thickness of hail cloud in North Xinjiang (8.90 km) is 1.25% greater than that in South Xinjiang (8.78 km); Influenced by human activities, industrial pollution and other factors, the mean concentration of condensation nuclei at the bottom of hail cloud in northern Xinjiang (396/cm3) is 65% higher than that in southern Xinjiang (240/cm3), which is dominated by agriculture. The mean maximum supersaturation of hail cloud bottom is 0.55% and 0.85% respectively. (4) Affected by the strong updraft, the growth time of hail cloud particles is short, and each growth zone develops slowly, and there is no rain embryo formation zone. Targeted seeding of hygroscopic nuclei in the middle and lower layers of the cloud in advance will promote the formation of precipitation at the bottom of the cloud as soon as possible, and excessive seeding of AgI ice nuclei near the 0 ℃ layer will compete for the supercooled water in the cloud, which can achieve the goal of increasing rain and preventing hail.
Available online: June 14, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061301
Abstract:
Using the observation data of microrain radar, raindrop disdrometerand rain gauge at Jingyu station Jilin Province from 24 to 25 August 2021, the vertical distribution of raindrop size and the evolution of microphysical characteristic parameters for a mixed cloud precipitation process at Changbai Mountain foothills are analyzed. The results show that the rainfall variation trends which are detected by microrain radar with high resolution of 150 m, raindrop disdrometer and rain gauge are basically consistent, but there are some deviations between observed values and inversion values. The Gamma function goodness of fit clocks up 0.99 for ground raindrop size distribution, which is better than that of micro rain radar.In addition, the fitting value for number concentration of large raindrops (D>3.0 mm)inverted by micro rain radar is significantly smaller.. Research also shows that different diameterraindrops have different contributions to microphysical parameters at different heights. For small raindrops (D≤1.0 mm), the contribution rate to rainfall intensity, reflectivity factor, liquid water content, and total number concentration decreases with degression of height meanwhile the contribution rate to these parameters increasesas height decreasing for medium raindrops（1.0 mm＜D≤3.0mm）and large raindrops. Besides, the evaporation and coalescence effect of raindrops show varieties in different precipitation stages. In the antecedent precipitation period, the evaporation effect of raindrops is stronger with higher temperature and lower relative humidity during the falling process.In the precipitation concentration period,the collision coalescence effect of raindrops is more obvious with the relative humidity approaching saturation meanwhile this effect of raindrops is particularly significant in the convective precipitation period.
Using the observation data of microrain radar, raindrop disdrometerand rain gauge at Jingyu station Jilin Province from 24 to 25 August 2021, the vertical distribution of raindrop size and the evolution of microphysical characteristic parameters for a mixed cloud precipitation process at Changbai Mountain foothills are analyzed. The results show that the rainfall variation trends which are detected by microrain radar with high resolution of 150 m, raindrop disdrometer and rain gauge are basically consistent, but there are some deviations between observed values and inversion values. The Gamma function goodness of fit clocks up 0.99 for ground raindrop size distribution, which is better than that of micro rain radar.In addition, the fitting value for number concentration of large raindrops (D>3.0 mm)inverted by micro rain radar is significantly smaller.. Research also shows that different diameterraindrops have different contributions to microphysical parameters at different heights. For small raindrops (D≤1.0 mm), the contribution rate to rainfall intensity, reflectivity factor, liquid water content, and total number concentration decreases with degression of height meanwhile the contribution rate to these parameters increasesas height decreasing for medium raindrops（1.0 mm＜D≤3.0mm）and large raindrops. Besides, the evaporation and coalescence effect of raindrops show varieties in different precipitation stages. In the antecedent precipitation period, the evaporation effect of raindrops is stronger with higher temperature and lower relative humidity during the falling process.In the precipitation concentration period,the collision coalescence effect of raindrops is more obvious with the relative humidity approaching saturation meanwhile this effect of raindrops is particularly significant in the convective precipitation period.
Available online: June 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031405
Abstract:
Abstract: Based on the ground observation data of daily precipitation, snow depth, daily mean temperature, daily minimum temperature and weather phenomena in Henan Province from November to March, 1991-2020, the low temperature threshold, the process and duration of cryogenic freezing rain and snow were determined by mathematical statistics. The factors that characterize the intensity of rain and snow and the degree of low temperature were selected to construct the meteorological index of cryogenic freezing rain and snow. The calculation and standardization of the cryogenic freezing rain and snow meteorological index were carried out at each observation station over the past years, and the standard deviation classification method was adopted, combined with the percentage distribution of each interval of the standardized meteorological index and the practical performance. Based on the above operations, the cryogenic freezing rain and snow events were divided into four levels: light, medium, heavy and extra heavy, respectively. The meteorological index and its standardized calculation of cryogenic freezing rain and snow at each observation station were carried out. According to the classification standard, the frequency of cryogenic freezing rain and snow of the multi-year average of each station and the representative stations in the past years were classified and counted. The results showed that: The mountainous area of western Henan is a high incidence area of cryogenic freezing rain and snow, while the basin of southwestern Henan and northwestern Henan are the low incidence areas. The multi-year average frequency of occurrence at all sites showed a decreasing trend from light to extra heavy. There is not a positive correlation between latitude and the frequency of cryogenic freezing rain and snow, and extra-heavy events occur even more frequently at low-latitude sites than at high-latitude and mountain sites.
Abstract: Based on the ground observation data of daily precipitation, snow depth, daily mean temperature, daily minimum temperature and weather phenomena in Henan Province from November to March, 1991-2020, the low temperature threshold, the process and duration of cryogenic freezing rain and snow were determined by mathematical statistics. The factors that characterize the intensity of rain and snow and the degree of low temperature were selected to construct the meteorological index of cryogenic freezing rain and snow. The calculation and standardization of the cryogenic freezing rain and snow meteorological index were carried out at each observation station over the past years, and the standard deviation classification method was adopted, combined with the percentage distribution of each interval of the standardized meteorological index and the practical performance. Based on the above operations, the cryogenic freezing rain and snow events were divided into four levels: light, medium, heavy and extra heavy, respectively. The meteorological index and its standardized calculation of cryogenic freezing rain and snow at each observation station were carried out. According to the classification standard, the frequency of cryogenic freezing rain and snow of the multi-year average of each station and the representative stations in the past years were classified and counted. The results showed that: The mountainous area of western Henan is a high incidence area of cryogenic freezing rain and snow, while the basin of southwestern Henan and northwestern Henan are the low incidence areas. The multi-year average frequency of occurrence at all sites showed a decreasing trend from light to extra heavy. There is not a positive correlation between latitude and the frequency of cryogenic freezing rain and snow, and extra-heavy events occur even more frequently at low-latitude sites than at high-latitude and mountain sites.
Available online: June 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.052801
Abstract:
In order to enhance the prediction accuracy of 0-2 h now-casting of short-time heavy precipitation and thunderstorm gale, this paper proposes a severe convection probability now-casting method based on the vertical profile characteristics of the dual-polarization radar (referred to as the CSCPVP method). By using the improved Bayesian probability method, the vertical profile characteristics of polarization radar of two types of severe convection disasters are introduced into the extrapolation model to realize the advanced identification of severe convection attributes, and the broad constraints of regional model prediction are integrated to ensure that the proximity extrapolation prediction results of severe convection are more consistent with the actual dynamic and microphysical characteristics. The evaluation results of the entire flood season (June-September 2023) in Zhejiang show that the CSCPVP method has significantly improved 0-2 h now-casting ability of two types of severe convection than the existing operational methods. The new method significantly improves 0-2 h now-casting ability of systematic, local and distributed classified severe convection (the critical success index of short-time heavy precipitation increases from 8%-16% to 22%-26%; The critical success index of thunderstorm gale was increased from 7% to 10%-11%), which effectively improved the problem of false alarms and missing prediction.
In order to enhance the prediction accuracy of 0-2 h now-casting of short-time heavy precipitation and thunderstorm gale, this paper proposes a severe convection probability now-casting method based on the vertical profile characteristics of the dual-polarization radar (referred to as the CSCPVP method). By using the improved Bayesian probability method, the vertical profile characteristics of polarization radar of two types of severe convection disasters are introduced into the extrapolation model to realize the advanced identification of severe convection attributes, and the broad constraints of regional model prediction are integrated to ensure that the proximity extrapolation prediction results of severe convection are more consistent with the actual dynamic and microphysical characteristics. The evaluation results of the entire flood season (June-September 2023) in Zhejiang show that the CSCPVP method has significantly improved 0-2 h now-casting ability of two types of severe convection than the existing operational methods. The new method significantly improves 0-2 h now-casting ability of systematic, local and distributed classified severe convection (the critical success index of short-time heavy precipitation increases from 8%-16% to 22%-26%; The critical success index of thunderstorm gale was increased from 7% to 10%-11%), which effectively improved the problem of false alarms and missing prediction.
Available online: June 04, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.030501
Abstract:
In order to explore the possible formation mechanism and flow pattern of extreme precipitation caused by the echo training of typhoon rainbands, we researched the circulation situation and the convection organization of there echo training processes after the landfall of the typhoon Soudelor (No.1513, process 1)，the typhoon Fitow (No.1323, process 2) and the typhoon Matsa (No.0509, process 3) by using multiple observation data and the ERA5 reanalysis data. The results show that the rainstorms of the three processes all occurred on the windward slope of the hills at the eastern part of Zhejiang province, directions of the rain belts were consistent with the background air flows, and convergence of water vapor flux were mainly concentrated below 850 hPa. In process 1, the rain belt happend between the low pressure and the subtropical high, the vertical wind shear and the CAPE are large, and the water vapor comes from tropical ocean surface and the wet layer is thick. Process 2 takes place in a saddle-shaped field between the residual vortex of a typhoon over land and another typhoon over the sea, and the vertical wind shear and CAPE were weak, water vapor comes from the sea surface at mid-latitude, and the wet layer is located in the middle and lower level of the troposphere. Process 3 is caused by the spiral rain band in core region of typhoon, the vertical wind shear is strong and the CAPE is the minimum. The structure and organization of the rain belts in the three process are obviously different. In Process 1, the boundary layer convergence and the convective system are the most highly developed, the baroclinic structure of the mesoscale convergence line promotes the uplift of warm and humid air from the sea surface, and the convergence field strengthenned the degree of organization. In Process 2, the wind direction of the weak cold pool is opposite to the easterly airflow, while with similar wind speed and shallow convergence, the new cells continue to form at the eastern boundary of the rain belt, and disappear at the western boundary, the stagnation of rain belt caused continuous belt-like heavy rainfall area. In Process 3, the spiral bands were affected by the typhoon vortex dynamics, the rain belts developed lowly, and the structure tilts slightly to the outside, and the rain belt developed with the wind speed convergence caused by the fluctuating of southeast jet, which resulted in the echo training with the largest hourly rainfall intensity among the three processes. The above facts show that the echo training of typhoon rainbands that causes extreme precipitation is formed in various ways, and the short-term forecast faces challenges.
In order to explore the possible formation mechanism and flow pattern of extreme precipitation caused by the echo training of typhoon rainbands, we researched the circulation situation and the convection organization of there echo training processes after the landfall of the typhoon Soudelor (No.1513, process 1)，the typhoon Fitow (No.1323, process 2) and the typhoon Matsa (No.0509, process 3) by using multiple observation data and the ERA5 reanalysis data. The results show that the rainstorms of the three processes all occurred on the windward slope of the hills at the eastern part of Zhejiang province, directions of the rain belts were consistent with the background air flows, and convergence of water vapor flux were mainly concentrated below 850 hPa. In process 1, the rain belt happend between the low pressure and the subtropical high, the vertical wind shear and the CAPE are large, and the water vapor comes from tropical ocean surface and the wet layer is thick. Process 2 takes place in a saddle-shaped field between the residual vortex of a typhoon over land and another typhoon over the sea, and the vertical wind shear and CAPE were weak, water vapor comes from the sea surface at mid-latitude, and the wet layer is located in the middle and lower level of the troposphere. Process 3 is caused by the spiral rain band in core region of typhoon, the vertical wind shear is strong and the CAPE is the minimum. The structure and organization of the rain belts in the three process are obviously different. In Process 1, the boundary layer convergence and the convective system are the most highly developed, the baroclinic structure of the mesoscale convergence line promotes the uplift of warm and humid air from the sea surface, and the convergence field strengthenned the degree of organization. In Process 2, the wind direction of the weak cold pool is opposite to the easterly airflow, while with similar wind speed and shallow convergence, the new cells continue to form at the eastern boundary of the rain belt, and disappear at the western boundary, the stagnation of rain belt caused continuous belt-like heavy rainfall area. In Process 3, the spiral bands were affected by the typhoon vortex dynamics, the rain belts developed lowly, and the structure tilts slightly to the outside, and the rain belt developed with the wind speed convergence caused by the fluctuating of southeast jet, which resulted in the echo training with the largest hourly rainfall intensity among the three processes. The above facts show that the echo training of typhoon rainbands that causes extreme precipitation is formed in various ways, and the short-term forecast faces challenges.
Available online: May 30, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.052201
Abstract:
Based on the observational datasets from National Meteorological Information Center (NMIC) of China and NCEP/NCAR reanalysis, the characteristics of spatial-temporal distributions of climate anomalies in winter 2023/2024 and its possible mechanisms are analyzed. In the winter of 2023/2024, the average temperature in China was 0.3℃ higher than climatology. The fluctuation of temperature is significant, with warmer early winter and colder late winter. The average precipitation was 19.8% more than climatology, with above normal precipitation for most parts of central and eastern China. The intensity of East Asian winter monsoon and Siberian high was near normal. The East Asian trough was weak than normal. The 500hPa geopotential height in the middle and high latitudes of Eurasia was low in the west and high in the east, with significant subseasonal fluctuation. Zonal atmospheric circulation prevails in December 2023 and January 2024, and transition to meridional patterns in February 2024, which was favorable for cold surge outbreak. In response to the synergistic effect of El Ni?o mature phase, warm tropical Indian and Atlantic ocean, cold phase of Pacific decadal oscillation, an anomalous lower tropospheric anticyclone developed in the western North Pacific, the western Pacific subtropical high intensified and extends westward, a Rossby wave train propagates along Asian westerly jet in the upper troposphere, which was favorable for the water vapor transport into central and eastern China. The confluence of cold air intrusion and warm air leads to frequent snow and rain process in central and eastern China.
Based on the observational datasets from National Meteorological Information Center (NMIC) of China and NCEP/NCAR reanalysis, the characteristics of spatial-temporal distributions of climate anomalies in winter 2023/2024 and its possible mechanisms are analyzed. In the winter of 2023/2024, the average temperature in China was 0.3℃ higher than climatology. The fluctuation of temperature is significant, with warmer early winter and colder late winter. The average precipitation was 19.8% more than climatology, with above normal precipitation for most parts of central and eastern China. The intensity of East Asian winter monsoon and Siberian high was near normal. The East Asian trough was weak than normal. The 500hPa geopotential height in the middle and high latitudes of Eurasia was low in the west and high in the east, with significant subseasonal fluctuation. Zonal atmospheric circulation prevails in December 2023 and January 2024, and transition to meridional patterns in February 2024, which was favorable for cold surge outbreak. In response to the synergistic effect of El Ni?o mature phase, warm tropical Indian and Atlantic ocean, cold phase of Pacific decadal oscillation, an anomalous lower tropospheric anticyclone developed in the western North Pacific, the western Pacific subtropical high intensified and extends westward, a Rossby wave train propagates along Asian westerly jet in the upper troposphere, which was favorable for the water vapor transport into central and eastern China. The confluence of cold air intrusion and warm air leads to frequent snow and rain process in central and eastern China.
Available online: May 22, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031403
Abstract:
Based on hourly precipitation data from the National Meteorological Information Center of the China Meteorological Administration, combined with the diversity of the terrain, the temporal and spatial characteristics of hourly precipitation, as well as characteristics of different types of Hourly Heavy Rainfall Event（HHRE） before（1992-2002）and after（2003-2021）the impoundment in Three Gorges Reservoir Area in the summer（from June to August）are analyzed. The results show that:（1）After impoundment, the precipitation and frequency decrease but intensity increases, while the change trends of the three are not significant. There is an obvious geographical distribution pattern for precipitation changes, with precipitation, frequency and intensity increasing in the central north of Three Gorges Reservoir Area, mostly located in the north of the Yangtze River, and the precipitation and frequency decreasing in the southwest while the intensity decreasing in the central south and northwest of Three Gorges Reservoir Area, mostly located south of 31°N.（2）There is a spatial distribution difference in the diurnal peak phases of precipitation, frequency, and intensity of hourly precipitation before and after impoundment, with the degree of difference being as follows: precipitation intensity>precipitation>precipitation frequency. After impoundment, the number of stations increases with increasing trend for precipitation, frequency and intensity, and the diurnal peak phases of precipitation and intensity have phase shift features in high altitude mountainous areas..（3）There is no significant change in the precipitation probability and proportion of hourly precipitation at various grades before and after impoundment. The precipitation probability shows the maximum（about 42%）at the grade of [0.1, 0.5）mm, and the minimum（about 1%）at the grade of ≥20 mm. The precipitation proportion shows the maximum（about 35%）at the grade of [1, 5）mm, the minimum（not more than 4%）at the grade of [0.1, 0.5）mm, and about 15% at the grade of ≥20 mm.（4）The daily variation characteristics of hourly precipitation after the impoundment are more obvious. The bimodal structures of precipitation and frequency of hourly precipitation at the grade of ≥20 mm are more prominent, while the peak time ranges of precipitation and frequency of hourly precipitation at other grades tend to expand, while the diurnal scale fluctuations of hourly precipitation intensity at each grade are more frequent.（5）Analysis of different duration types of HHREs shows that both before and after impoundment, the short-duration type of HHRE is the highest（more than 50%）, followed by medium-duration type（less than 30%）, and the long-duration type is the lowest（less than 20%）. The short-duration type of HHREs mostly start in the afternoon, while the other two types of HHREs mostly start at night. After impoundment, it is beneficial for HHRE maintenance, with a decrease in the proportion of short-duration type of HHRE and an increase in the proportion of medium-duration and long-duration types of HHREs, and the probability of the former starting at noon and afternoon increases, while the probability of the latter two starting in the morning increases.
Based on hourly precipitation data from the National Meteorological Information Center of the China Meteorological Administration, combined with the diversity of the terrain, the temporal and spatial characteristics of hourly precipitation, as well as characteristics of different types of Hourly Heavy Rainfall Event（HHRE） before（1992-2002）and after（2003-2021）the impoundment in Three Gorges Reservoir Area in the summer（from June to August）are analyzed. The results show that:（1）After impoundment, the precipitation and frequency decrease but intensity increases, while the change trends of the three are not significant. There is an obvious geographical distribution pattern for precipitation changes, with precipitation, frequency and intensity increasing in the central north of Three Gorges Reservoir Area, mostly located in the north of the Yangtze River, and the precipitation and frequency decreasing in the southwest while the intensity decreasing in the central south and northwest of Three Gorges Reservoir Area, mostly located south of 31°N.（2）There is a spatial distribution difference in the diurnal peak phases of precipitation, frequency, and intensity of hourly precipitation before and after impoundment, with the degree of difference being as follows: precipitation intensity>precipitation>precipitation frequency. After impoundment, the number of stations increases with increasing trend for precipitation, frequency and intensity, and the diurnal peak phases of precipitation and intensity have phase shift features in high altitude mountainous areas..（3）There is no significant change in the precipitation probability and proportion of hourly precipitation at various grades before and after impoundment. The precipitation probability shows the maximum（about 42%）at the grade of [0.1, 0.5）mm, and the minimum（about 1%）at the grade of ≥20 mm. The precipitation proportion shows the maximum（about 35%）at the grade of [1, 5）mm, the minimum（not more than 4%）at the grade of [0.1, 0.5）mm, and about 15% at the grade of ≥20 mm.（4）The daily variation characteristics of hourly precipitation after the impoundment are more obvious. The bimodal structures of precipitation and frequency of hourly precipitation at the grade of ≥20 mm are more prominent, while the peak time ranges of precipitation and frequency of hourly precipitation at other grades tend to expand, while the diurnal scale fluctuations of hourly precipitation intensity at each grade are more frequent.（5）Analysis of different duration types of HHREs shows that both before and after impoundment, the short-duration type of HHRE is the highest（more than 50%）, followed by medium-duration type（less than 30%）, and the long-duration type is the lowest（less than 20%）. The short-duration type of HHREs mostly start in the afternoon, while the other two types of HHREs mostly start at night. After impoundment, it is beneficial for HHRE maintenance, with a decrease in the proportion of short-duration type of HHRE and an increase in the proportion of medium-duration and long-duration types of HHREs, and the probability of the former starting at noon and afternoon increases, while the probability of the latter two starting in the morning increases.
Available online: May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.033002
Abstract:
Based on the squall line recognition standards, 36 squall line processes were identified using the radar combination reflectance mosaic product from May to September 2015 to 2020 in Liaoning Province,and the squall line characteristics and several different formation environment characteristics were summarized. The results show that: (1) The area with the largest frequency of squall line formation in Liaoning Province is obviously from the northwest of Liaoning Province and Chifeng City to Aohan Banner, followed by the west of Bohai Sea to the sea surface of Bohai Strait, and the area with the lowest frequency of squall line formation is the mountain line of Tangshan and Qinhuangdao in the east of Hebei Province. (2)The vast majority of squall line processes occur in June and August, while the least squall line processes occur in May. Squall lines are mainly formed from 12:00 to 21:00, and from 14:00 to 17:00 is the concentration period of squall lines. The length of squall line is between 114 km and 273 km, the maximum reflectivity is 65 bz, the average life cycle is 3.2 hours, and the average moving speed is 59.4 km/h (16.5 m/s). (3) The squall line process in Liaoning Province is 33.3% of the fault line, 19.4% of the rear extension type, 36.1% of the fragment type, and 11.1% of the stratiform cloud embedding type. The main organizational form is stratiform cloud trailing type TS, parallel stratiform cloud type PS and stratiform cloud leading type LS have fewer occurrences. 55.6% of squall lines dissipated in the form of reverse broken lines, and 8.3% of squall lines dissipated in the form of contraction lines. 36.1% of squall lines dissipated in the form of reverse fault zone. (4) In the circulation situation of squall line formation in Liaoning, the cold vortex front type is the most common, followed by the low trough front type. The circulation situation of squall line formation in Liaoning is the cold vortex rear type, accounting for 16.7%. The convective effective potential energy and the sink convective effective potential energy of each circulation pattern show the characteristics of "double 1000". Different circulation patterns have different characteristics in water vapor supply, stratification instability, vertical wind shear and other physical quantities.
Based on the squall line recognition standards, 36 squall line processes were identified using the radar combination reflectance mosaic product from May to September 2015 to 2020 in Liaoning Province,and the squall line characteristics and several different formation environment characteristics were summarized. The results show that: (1) The area with the largest frequency of squall line formation in Liaoning Province is obviously from the northwest of Liaoning Province and Chifeng City to Aohan Banner, followed by the west of Bohai Sea to the sea surface of Bohai Strait, and the area with the lowest frequency of squall line formation is the mountain line of Tangshan and Qinhuangdao in the east of Hebei Province. (2)The vast majority of squall line processes occur in June and August, while the least squall line processes occur in May. Squall lines are mainly formed from 12:00 to 21:00, and from 14:00 to 17:00 is the concentration period of squall lines. The length of squall line is between 114 km and 273 km, the maximum reflectivity is 65 bz, the average life cycle is 3.2 hours, and the average moving speed is 59.4 km/h (16.5 m/s). (3) The squall line process in Liaoning Province is 33.3% of the fault line, 19.4% of the rear extension type, 36.1% of the fragment type, and 11.1% of the stratiform cloud embedding type. The main organizational form is stratiform cloud trailing type TS, parallel stratiform cloud type PS and stratiform cloud leading type LS have fewer occurrences. 55.6% of squall lines dissipated in the form of reverse broken lines, and 8.3% of squall lines dissipated in the form of contraction lines. 36.1% of squall lines dissipated in the form of reverse fault zone. (4) In the circulation situation of squall line formation in Liaoning, the cold vortex front type is the most common, followed by the low trough front type. The circulation situation of squall line formation in Liaoning is the cold vortex rear type, accounting for 16.7%. The convective effective potential energy and the sink convective effective potential energy of each circulation pattern show the characteristics of "double 1000". Different circulation patterns have different characteristics in water vapor supply, stratification instability, vertical wind shear and other physical quantities.
Available online: May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.051601
Abstract:
Based on the high spatial-temporal resolution data such as ERA5(0.25°×0.25°) reanalysis data, automatic weather stations data, doppler weather radar data and the retrieval data from Variational Doppler Radar Analysis System(VDRAS), we compared and analyzed the mesoscale characteristics and triggering mechanism of three local sudden rainstorms in the urban area of Tianjin on 22 July 2018, 18 July 2019 and 23 August 2021.The results show that there is no obvious synoptic scale system leading the three local sudden heavy rainstorms, but the ambient atmosphere has a high convective available potential energy (CAPE) and a low convective inhibition energy (CIN). The lifting condensation height (LCL) was 0.2~ 0.4 km, and there was a certain wet layer in the lower level. The occurrence of local sudden rainstorm was mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the local sudden rainstorm, the difference of temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious non-uniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of local convection. In addition, before the occurrence of local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened, resulting in the convergence of wind speed. The thermal low pressure of the urban heat island and the disturbance of sea breeze made the mesoscale convergence intensity significantly strengthened, which was the main reason for the occurrence of local sudden rainstorm. γ-mesoscale convective cells were triggered at the edge of the strong convergence center.
Based on the high spatial-temporal resolution data such as ERA5(0.25°×0.25°) reanalysis data, automatic weather stations data, doppler weather radar data and the retrieval data from Variational Doppler Radar Analysis System(VDRAS), we compared and analyzed the mesoscale characteristics and triggering mechanism of three local sudden rainstorms in the urban area of Tianjin on 22 July 2018, 18 July 2019 and 23 August 2021.The results show that there is no obvious synoptic scale system leading the three local sudden heavy rainstorms, but the ambient atmosphere has a high convective available potential energy (CAPE) and a low convective inhibition energy (CIN). The lifting condensation height (LCL) was 0.2~ 0.4 km, and there was a certain wet layer in the lower level. The occurrence of local sudden rainstorm was mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the local sudden rainstorm, the difference of temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious non-uniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of local convection. In addition, before the occurrence of local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened, resulting in the convergence of wind speed. The thermal low pressure of the urban heat island and the disturbance of sea breeze made the mesoscale convergence intensity significantly strengthened, which was the main reason for the occurrence of local sudden rainstorm. γ-mesoscale convective cells were triggered at the edge of the strong convergence center.
Available online: May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.051701
Abstract:
Based on the outpatient and inpatient data of heatstroke in Tianjin from 2016 to 2020, a comparative analysis of the relationship between meteorological factors and the heatstroke visit rate was conducted using the Generalized Additive Model (GAM) and Distributed Lag Nonlinear Model (DLNM). By introducing the human heat balance model and predicted mean vote (PMV), a localized heatstroke meteorological risk warning index was established. The results show that the number of outpatient and inpatient cases of heatstroke in Tianjin is concentrated from late June to early August each year, with 84% of the peak heatstroke days occurring in 6 continuous weather process over the 5 years. The occurrence is most correlated with the meteorological conditions of the current day and the previous day, with a significant increase in heatstroke cases when the maximum temperature exceeds 35°C. Males are more susceptible to heatstroke than females, and the visit rate of the elderly is significantly higher than the general population. The heatstroke visit rate is positively correlated with average temperature, maximum temperature, relative humidity, and solar radiation intensity, with the strongest correlation with average temperature and a negative correlation with wind speed. Introducing the human heat balance model, PMV shows a higher correlation with the heatstroke visit rate than any single meteorological factor, indicating PMV has a clear advantage in evaluating heatstroke meteorological risk. A forecasting equation with PMV as the key indicator was developed, which demonstrated significant advantages in predicting heatstroke high-incidence events.
Based on the outpatient and inpatient data of heatstroke in Tianjin from 2016 to 2020, a comparative analysis of the relationship between meteorological factors and the heatstroke visit rate was conducted using the Generalized Additive Model (GAM) and Distributed Lag Nonlinear Model (DLNM). By introducing the human heat balance model and predicted mean vote (PMV), a localized heatstroke meteorological risk warning index was established. The results show that the number of outpatient and inpatient cases of heatstroke in Tianjin is concentrated from late June to early August each year, with 84% of the peak heatstroke days occurring in 6 continuous weather process over the 5 years. The occurrence is most correlated with the meteorological conditions of the current day and the previous day, with a significant increase in heatstroke cases when the maximum temperature exceeds 35°C. Males are more susceptible to heatstroke than females, and the visit rate of the elderly is significantly higher than the general population. The heatstroke visit rate is positively correlated with average temperature, maximum temperature, relative humidity, and solar radiation intensity, with the strongest correlation with average temperature and a negative correlation with wind speed. Introducing the human heat balance model, PMV shows a higher correlation with the heatstroke visit rate than any single meteorological factor, indicating PMV has a clear advantage in evaluating heatstroke meteorological risk. A forecasting equation with PMV as the key indicator was developed, which demonstrated significant advantages in predicting heatstroke high-incidence events.
Available online: May 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.020701
Abstract:
Based on Guangdong meteorological disaster archives, ERA5 reanalysis data and Doppler radar data, the spatiotemporal distribution, weather background and parent storm patterns of Guangdong tornadoes during 1961-2022 are analyzed, results are as follows:In the past 62 years, Guangdong has recorded a total of 225 tornadoes. Among them, since 2006, when multiple sources of observation data are relatively complete, about 6 tornadoes have occurred annually, about 50% of tornadoes occur in the background of tropical cyclone weather, followed by 40% of tornadoes in the Westerlies weather system, but the number of tornadoes fluctuates greatly year by year, up to 17 (2008), and only one tornado or no tornado record in some years. Tornadoes mainly occur from April to September, with 54% occurring from April to June, mostly in the context of the westerly weather system, and 34% occurring from July to September, mainly in the context of tropical cyclones and disturbances. More than 85% of tornadoes occur between 0800-2000 BJT (Beijing Time, the same below), with the highest occurrence occurring between 1400-1800 BJT (accounting for about 40%). Tornadoes occur most frequently in the Pearl River Delta, Leizhou Peninsula and Chaoshan Plain. There are few tornadoes in the northern mountainous areas. Foshan, Zhanjiang and Guangzhou are the cities with the highest incidence of tornadoes. Among the convection patterns that generate tornadoes in Guangdong, more than 50% of tornadoes are generated from miniature supercells embedded in the zonal convective system, and about 30% of tornadoes are generated from supercell in the multicells storm system. Different from the situation that isolated convection cell in the United States are more likely to generate tornadoes, the relative frequency of isolated convection cell that generate tornadoes in Guangdong is very low, accounting for about 5%. More than 90% of tornado parent storms have low-level mesocyclone, but only about 44% of tornado parent storms are accompanied by low-level TVS. Strong tornadoes (EF2+) are typically characterized by low-level mesocyclones with rotational speeds exceeding 20 m·s-1 and TVS velocity differences exceeding 40 m·s-1 .
Based on Guangdong meteorological disaster archives, ERA5 reanalysis data and Doppler radar data, the spatiotemporal distribution, weather background and parent storm patterns of Guangdong tornadoes during 1961-2022 are analyzed, results are as follows:In the past 62 years, Guangdong has recorded a total of 225 tornadoes. Among them, since 2006, when multiple sources of observation data are relatively complete, about 6 tornadoes have occurred annually, about 50% of tornadoes occur in the background of tropical cyclone weather, followed by 40% of tornadoes in the Westerlies weather system, but the number of tornadoes fluctuates greatly year by year, up to 17 (2008), and only one tornado or no tornado record in some years. Tornadoes mainly occur from April to September, with 54% occurring from April to June, mostly in the context of the westerly weather system, and 34% occurring from July to September, mainly in the context of tropical cyclones and disturbances. More than 85% of tornadoes occur between 0800-2000 BJT (Beijing Time, the same below), with the highest occurrence occurring between 1400-1800 BJT (accounting for about 40%). Tornadoes occur most frequently in the Pearl River Delta, Leizhou Peninsula and Chaoshan Plain. There are few tornadoes in the northern mountainous areas. Foshan, Zhanjiang and Guangzhou are the cities with the highest incidence of tornadoes. Among the convection patterns that generate tornadoes in Guangdong, more than 50% of tornadoes are generated from miniature supercells embedded in the zonal convective system, and about 30% of tornadoes are generated from supercell in the multicells storm system. Different from the situation that isolated convection cell in the United States are more likely to generate tornadoes, the relative frequency of isolated convection cell that generate tornadoes in Guangdong is very low, accounting for about 5%. More than 90% of tornado parent storms have low-level mesocyclone, but only about 44% of tornado parent storms are accompanied by low-level TVS. Strong tornadoes (EF2+) are typically characterized by low-level mesocyclones with rotational speeds exceeding 20 m·s-1 and TVS velocity differences exceeding 40 m·s-1 .
QIN Hao, FAN Jiao, NONG Mengsong, LAI Zhenquan, zhaishunan, LIU Le, LIU Xiaomei, PANG Fang, ZHOU Yijing, QIU Zi
Available online: May 07, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.030801
Abstract:
Guangxi encountered a double convective bands process from 20:00 BT 25 March to 08:00 BT 26 March 2023, which are significantly different from that of the double traditional rain belts, resulting in a significant deviation in the subjective forecast. Based on multi-source observation data and ERA5 reanalysis data, the Rossby wave energy dispersion, moist potential vorticity and horizontal frontogenic forcing were diagnosis and analyzed in this process. The results show that the process occurred under the background of large-scale circulation adjustment. The two Rossby wave trains originated from the polar vortex and the Black Sea in the middle and high-latitude jointly promoted the gradual vertical rotation of the northeast transversal trough, and guided the mid and high latitude cold air further southward. During this period, the south branch trough in the low latitude gradually moved eastward, which provided the dynamic lifting above the cold cushion in Guangxi, and also promoted the convergence of cold and warm air in the low level in Guangxi. With the addition of cold air to the south and southerly winds advance northward under the inertial oscillation, the convergence of warm and cold air in Guangxi was enhanced, and the enhancement of atmospheric moist baroclinicity leads to the development of moist potential vorticity, resulting in conditional symmetric instability of stratification. Warm and moist air climbed from south to north to the conditional symmetric instability area near 700 hPa, and then combined with the positive vorticity advection in front of the upper level trough to trigger elevated convection, resulting in the development of the northern branch convective band. Influenced by the special topography of Guangxi, the favorable configuration of the θse isoline and the flow formed a tensile deformation effect, resulting in frontogenic forcing, which triggered the initial convection in the south branch of Northeast Vietnam. The large θse latitudinal gradient and strong vertical wind shear in the low level of the central Beibu Gulf resulted in strong moist baroclinicity, which promoted the organization development of the southern branch convective system when it passed through, and formed bow echo due to the mid-level dry air ensnagging.
Guangxi encountered a double convective bands process from 20:00 BT 25 March to 08:00 BT 26 March 2023, which are significantly different from that of the double traditional rain belts, resulting in a significant deviation in the subjective forecast. Based on multi-source observation data and ERA5 reanalysis data, the Rossby wave energy dispersion, moist potential vorticity and horizontal frontogenic forcing were diagnosis and analyzed in this process. The results show that the process occurred under the background of large-scale circulation adjustment. The two Rossby wave trains originated from the polar vortex and the Black Sea in the middle and high-latitude jointly promoted the gradual vertical rotation of the northeast transversal trough, and guided the mid and high latitude cold air further southward. During this period, the south branch trough in the low latitude gradually moved eastward, which provided the dynamic lifting above the cold cushion in Guangxi, and also promoted the convergence of cold and warm air in the low level in Guangxi. With the addition of cold air to the south and southerly winds advance northward under the inertial oscillation, the convergence of warm and cold air in Guangxi was enhanced, and the enhancement of atmospheric moist baroclinicity leads to the development of moist potential vorticity, resulting in conditional symmetric instability of stratification. Warm and moist air climbed from south to north to the conditional symmetric instability area near 700 hPa, and then combined with the positive vorticity advection in front of the upper level trough to trigger elevated convection, resulting in the development of the northern branch convective band. Influenced by the special topography of Guangxi, the favorable configuration of the θse isoline and the flow formed a tensile deformation effect, resulting in frontogenic forcing, which triggered the initial convection in the south branch of Northeast Vietnam. The large θse latitudinal gradient and strong vertical wind shear in the low level of the central Beibu Gulf resulted in strong moist baroclinicity, which promoted the organization development of the southern branch convective system when it passed through, and formed bow echo due to the mid-level dry air ensnagging.
Available online: April 25, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022401
Abstract:
Based on the Tianjin Doppler radar data, conventional observation, ground automatic station meteorological data, ERA5 reanalysis data and VDRAS data, a rare heavy precipitation(HP) supercell storm which was guided by a multi-cell strong storm occurred in the eastern Hebei on 19 June 2017 was analyzed, the evolution characteristics and maintenance mechanism of supercell storms are mainly discussed. The results indicate that the sea-breeze front and the gust front of the multi-cell strong storm provide better dynamic conditions, the high temperature and high humidity area of tongue shaped by sea-breeze front and the gust front in the lower layer surrounding provide better thermal conditions for the formation of the supercell, when the convection cell moves into the tongue area, then it rapidly develops into a supercell and moves southeastward along the outflow boundary of multi-cell strong storm. The relatively stable gust front provided by the slowly weakening severe thunderstorm not only provides long-term thermodynamic conditions for the development and maintenance of supercell, but also guides its movement, which is of great significance for the short-term and imminent warning of the convective weather. At the beginning of the formation of supercell, affected by the outflow of multi-cell strong storm cold pool, the southerly winds near the ground turn to stronger easterly winds, the configuration of mesoscale environment has changed significantly, the vertical wind shear of 0~6 km increases to 27 m.s-1 and the shear of 0~3 km increases to 17~19 m.s-1 is the main reason for the rapid formation of mesocyclone, Secondly, the strong vertical vorticity advection on the convergence line is also conducive to the formation and maintenance of mesocyclone. The reason why the cyclone in supercell started at the lower level is that the vertical wind shear of 0~3 km obtained from VDRAS data is always about 20 m.s-1, the oblique vortex effect is obvious which provides a large and long-term horizontal vorticity input for the development and maintenance of supercell. During the formation and development of supercell, the relative helicity (SRH) of the storm is between 140 and 171 m2.s-2, which is more than 150 m2.s-2 for most of the time, Before the formation of supercell and near the dissipation stage, the SRH is significantly smaller, which is less than 150 m2.s-2 for most of the time, that indicates the SRH has a clear indication for the occurrence and development of supercell. The outflow of the cold pool precedes the formation of the supercell, which strengthens the convergence and uplift of the inflow, and is conducive to the development and maintenance of the supercell, In addition, there are more cells splitting from parent storm, which to some extent weakens the strong development of the supercell, but it just makes the sinking outflow not too strong and causes the gust front to move away quickly, making the cold pool always maintain a certain intensity, at the same time, the front of multi-cell storm provides a stable vertical wind shear of 0~3 km (maintained at about 20 m.s-1) for the supercell, this results in a long-term balance between the wind shear and the strength of the cold pool, and finally the supercell maintains a stable state for a long time. In a word, the main reason why the supercell maintains self-organization for a long time is that the appropriate vertical wind shear provided by the mesoscale environment keeps balance with the development of the storm.
Based on the Tianjin Doppler radar data, conventional observation, ground automatic station meteorological data, ERA5 reanalysis data and VDRAS data, a rare heavy precipitation(HP) supercell storm which was guided by a multi-cell strong storm occurred in the eastern Hebei on 19 June 2017 was analyzed, the evolution characteristics and maintenance mechanism of supercell storms are mainly discussed. The results indicate that the sea-breeze front and the gust front of the multi-cell strong storm provide better dynamic conditions, the high temperature and high humidity area of tongue shaped by sea-breeze front and the gust front in the lower layer surrounding provide better thermal conditions for the formation of the supercell, when the convection cell moves into the tongue area, then it rapidly develops into a supercell and moves southeastward along the outflow boundary of multi-cell strong storm. The relatively stable gust front provided by the slowly weakening severe thunderstorm not only provides long-term thermodynamic conditions for the development and maintenance of supercell, but also guides its movement, which is of great significance for the short-term and imminent warning of the convective weather. At the beginning of the formation of supercell, affected by the outflow of multi-cell strong storm cold pool, the southerly winds near the ground turn to stronger easterly winds, the configuration of mesoscale environment has changed significantly, the vertical wind shear of 0~6 km increases to 27 m.s-1 and the shear of 0~3 km increases to 17~19 m.s-1 is the main reason for the rapid formation of mesocyclone, Secondly, the strong vertical vorticity advection on the convergence line is also conducive to the formation and maintenance of mesocyclone. The reason why the cyclone in supercell started at the lower level is that the vertical wind shear of 0~3 km obtained from VDRAS data is always about 20 m.s-1, the oblique vortex effect is obvious which provides a large and long-term horizontal vorticity input for the development and maintenance of supercell. During the formation and development of supercell, the relative helicity (SRH) of the storm is between 140 and 171 m2.s-2, which is more than 150 m2.s-2 for most of the time, Before the formation of supercell and near the dissipation stage, the SRH is significantly smaller, which is less than 150 m2.s-2 for most of the time, that indicates the SRH has a clear indication for the occurrence and development of supercell. The outflow of the cold pool precedes the formation of the supercell, which strengthens the convergence and uplift of the inflow, and is conducive to the development and maintenance of the supercell, In addition, there are more cells splitting from parent storm, which to some extent weakens the strong development of the supercell, but it just makes the sinking outflow not too strong and causes the gust front to move away quickly, making the cold pool always maintain a certain intensity, at the same time, the front of multi-cell storm provides a stable vertical wind shear of 0~3 km (maintained at about 20 m.s-1) for the supercell, this results in a long-term balance between the wind shear and the strength of the cold pool, and finally the supercell maintains a stable state for a long time. In a word, the main reason why the supercell maintains self-organization for a long time is that the appropriate vertical wind shear provided by the mesoscale environment keeps balance with the development of the storm.
Observation Analysis of Dual Polarization Radar andRaindrop Spectrumfor Microphysical Characteristic
Available online: April 12, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.092802
Abstract:
In order to investigate microphysical characteristic in the hailstorm, the dual polarization radar and raindrop spectrum data, with the hydrometer classification algorithm were used to analyse a hail weather occurred in Mount Tai on 1 June 2020, the distribution of the radar variable, hydrometer and the raindrop in the region around the Mount Tai station were obtained when the hailstorm cloud passed through the Mount Tai, the studies showed: 1) when the edge of hailstorm began to effect the Mount Tai station, the large gradient area of reflectivity (ZH), which coinciding with differential reflectivity(ZDR) arc position, was next to the Mount Tai station, the particles identified in ZDR arc were mainly composed of abundant big drop, which was formed by melting graupel particles over Mount Tai station; the structure of the raindrop spectrum was double-peak, the greater contribution to precipitation is 2-3mm particles. 2) When the main part of the hailstorm cloud influenced the Mount Tai station, there occurred three-body scattering echo in radial front of the station and overhang echo over the station, the particles in the vicinity of the station were mainly identified as hail; on the south side of Mount Tai station there occurred the bounded weak echoSregion(BWER), the convergent ascending motion was enhanced in the BWER, which was semi-surrounded by the large value of ZDR(ZDR ring), the particles in ZDR ring were mainly identified as big drop and hail, with small amount of graupel and wet snow; the contoured frequency by altitude diagram(CFAD) showed the ice phase process was enhanced, the hail particles under the -10℃ were mainly formed by the graupel particles between 0℃ and -10℃ layer riming the big drop and light rain particles carried by updrafts, these particles could not fall and collide to form larger precipitation particles during this period, therefore the structure of the raindrop spectrum became single-peak, the greater contribution to precipitation was 14-16mm particles. 3) When the hailstorm cloud left the Mount Tai station, CFAD showed the ZHcorresponding toSthe high frequency region decrease, the ice phase process was weaken, the efficiency of the cold cloud droplets attached to the ice crystals to converted into graupel was reduced, a large number of ice crystals and dry snow particles were identified above Mount Tai station, where the feature of the stratiform cloud precipitation appeared; big drop particles were formed by the melting hail, the structure of the raindrop spectrum became double-peak again, the second peak value of particles was 2-3mm, which contributed more to the precipitation.
In order to investigate microphysical characteristic in the hailstorm, the dual polarization radar and raindrop spectrum data, with the hydrometer classification algorithm were used to analyse a hail weather occurred in Mount Tai on 1 June 2020, the distribution of the radar variable, hydrometer and the raindrop in the region around the Mount Tai station were obtained when the hailstorm cloud passed through the Mount Tai, the studies showed: 1) when the edge of hailstorm began to effect the Mount Tai station, the large gradient area of reflectivity (ZH), which coinciding with differential reflectivity(ZDR) arc position, was next to the Mount Tai station, the particles identified in ZDR arc were mainly composed of abundant big drop, which was formed by melting graupel particles over Mount Tai station; the structure of the raindrop spectrum was double-peak, the greater contribution to precipitation is 2-3mm particles. 2) When the main part of the hailstorm cloud influenced the Mount Tai station, there occurred three-body scattering echo in radial front of the station and overhang echo over the station, the particles in the vicinity of the station were mainly identified as hail; on the south side of Mount Tai station there occurred the bounded weak echoSregion(BWER), the convergent ascending motion was enhanced in the BWER, which was semi-surrounded by the large value of ZDR(ZDR ring), the particles in ZDR ring were mainly identified as big drop and hail, with small amount of graupel and wet snow; the contoured frequency by altitude diagram(CFAD) showed the ice phase process was enhanced, the hail particles under the -10℃ were mainly formed by the graupel particles between 0℃ and -10℃ layer riming the big drop and light rain particles carried by updrafts, these particles could not fall and collide to form larger precipitation particles during this period, therefore the structure of the raindrop spectrum became single-peak, the greater contribution to precipitation was 14-16mm particles. 3) When the hailstorm cloud left the Mount Tai station, CFAD showed the ZHcorresponding toSthe high frequency region decrease, the ice phase process was weaken, the efficiency of the cold cloud droplets attached to the ice crystals to converted into graupel was reduced, a large number of ice crystals and dry snow particles were identified above Mount Tai station, where the feature of the stratiform cloud precipitation appeared; big drop particles were formed by the melting hail, the structure of the raindrop spectrum became double-peak again, the second peak value of particles was 2-3mm, which contributed more to the precipitation.
Available online: April 08, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.040101
Abstract:
The snowfall in Beijing on January 12, 2023 was the first snowfall appearing in early and mid-January in last 42 years, and the precipitation types underwent complex changes during this process. In this paper， we utilize various conventional and non-conventional observations such as cloud radar and micro rain radar (MMR) data as well as ERA5 reanalysis data to analyze this event, focusing on causes of complex phase distribution and variation. Our findings indicate the following: The low level warm and wet southerly jet stream provides abundant moisture for precipitation. However, a lack of uplifting of warm and wet air by cold east winds and weak upper trough results in relatively low precipitation amounts, meanwhile the northeast wind just above the surface did not play the role of cold cushion, which was not conducive to the maintenance of snow and snow in the whole city. The disparity in the height of the 0 ℃-layer between western and eastern Beijing, caused by low-level warm advection, explains the snowfall in the west and rain in the east. Additionally, the cooling effect caused by melting and evaporation process is the main reason for the rapid decrease of 0 ℃-layer height just lower than 500 m, which caused rain to snow in plain areas. Thickened > 0 ℃ warm layer and decreased snowflake size and density immediately above the melting layer caused snow to turn into rain reaching the ground. When it comes to forecasting precipitation types, deterministic models struggle to accurately depict the snow-melting process. However, short-range ensemble forecast results can compensate for the errors in deterministic models. Integrating cloud radar, micro rain radar, and microwave radiometer data ETC. enhances our ability to monitor and analyze snow formation within clouds and melting in the boundary layer, thus improving the accuracy of precipitation type now casting.
The snowfall in Beijing on January 12, 2023 was the first snowfall appearing in early and mid-January in last 42 years, and the precipitation types underwent complex changes during this process. In this paper， we utilize various conventional and non-conventional observations such as cloud radar and micro rain radar (MMR) data as well as ERA5 reanalysis data to analyze this event, focusing on causes of complex phase distribution and variation. Our findings indicate the following: The low level warm and wet southerly jet stream provides abundant moisture for precipitation. However, a lack of uplifting of warm and wet air by cold east winds and weak upper trough results in relatively low precipitation amounts, meanwhile the northeast wind just above the surface did not play the role of cold cushion, which was not conducive to the maintenance of snow and snow in the whole city. The disparity in the height of the 0 ℃-layer between western and eastern Beijing, caused by low-level warm advection, explains the snowfall in the west and rain in the east. Additionally, the cooling effect caused by melting and evaporation process is the main reason for the rapid decrease of 0 ℃-layer height just lower than 500 m, which caused rain to snow in plain areas. Thickened > 0 ℃ warm layer and decreased snowflake size and density immediately above the melting layer caused snow to turn into rain reaching the ground. When it comes to forecasting precipitation types, deterministic models struggle to accurately depict the snow-melting process. However, short-range ensemble forecast results can compensate for the errors in deterministic models. Integrating cloud radar, micro rain radar, and microwave radiometer data ETC. enhances our ability to monitor and analyze snow formation within clouds and melting in the boundary layer, thus improving the accuracy of precipitation type now casting.
Available online: April 02, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.021701
Abstract:
Lightning and conventional ground observations provide complementary atmospheric background information, and the combined assimilation of these two types of data has the potential to further improve the accuracy of forecasting severe convective weather compared to assimilating only one type of data. In this study, a mesoscale convective system occurred in Guangdong Province on June 16, 2017 as an example to analyze the effect of the combined assimilation of the above two kinds of data on the simulation and prediction of mesoscale convective system compared with the single assimilation of one of the two kinds of data. The lightning data is continuously assimilated into the model through the WRF-FDDA system with a lightning accumulation window of 15 minutes, the conventional observations data is assimilated into the model by the WRFDA-3DVAR system at one hour interval. The results show that the introduction of lightning data in the joint assimilation experiment improves the accuracy of updrafts, cold pools, and gust fronts in the background fields, which in turn improves the simulation and forecast accuracy of the convective system, compared with the assimilation of conventional ground observations only. The introduction of conventional ground observations in the joint assimilation experiment reduces the background field errors in temperature, water vapor, and wind fields over a larger area, suppresses the spurious convection in some areas, and overall improves the simulation and forecast accuracy of the convective system. The results of prediction skill score show that the combined assimilation of the two kinds of data also improved the prediction skill score of the analysis period and the forecast period to some extent.
Lightning and conventional ground observations provide complementary atmospheric background information, and the combined assimilation of these two types of data has the potential to further improve the accuracy of forecasting severe convective weather compared to assimilating only one type of data. In this study, a mesoscale convective system occurred in Guangdong Province on June 16, 2017 as an example to analyze the effect of the combined assimilation of the above two kinds of data on the simulation and prediction of mesoscale convective system compared with the single assimilation of one of the two kinds of data. The lightning data is continuously assimilated into the model through the WRF-FDDA system with a lightning accumulation window of 15 minutes, the conventional observations data is assimilated into the model by the WRFDA-3DVAR system at one hour interval. The results show that the introduction of lightning data in the joint assimilation experiment improves the accuracy of updrafts, cold pools, and gust fronts in the background fields, which in turn improves the simulation and forecast accuracy of the convective system, compared with the assimilation of conventional ground observations only. The introduction of conventional ground observations in the joint assimilation experiment reduces the background field errors in temperature, water vapor, and wind fields over a larger area, suppresses the spurious convection in some areas, and overall improves the simulation and forecast accuracy of the convective system. The results of prediction skill score show that the combined assimilation of the two kinds of data also improved the prediction skill score of the analysis period and the forecast period to some extent.
Available online: April 01, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.020401
Abstract:
This study employs observational data from stations in the eastern part of the southwestern region and ERA5 reanalysis data to examine the characteristics and causes of the inverse phase shift anomalies in winter temperatures (hereafter referred to as anomalous shifts) in this area. The findings indicate that post-2000, this region tends to experience a pattern of colder temperatures earlier in the winter followed by warmer temperatures later (referred to as P1 type), whereas a pattern of warmer temperatures followed by colder ones (P2 type) was more prevalent in the 1970s. During the occurrence of these anomalous shifts in winter temperatures, the 500 hPa geopotential height field reveals that the Tibetan Plateau plays a crucial role in the circulation system, even surpassing the influence of the Ural blocking high. At the 200 hPa wind field level, systems such as the westerly jet stream affect the East Asian winter monsoon, thereby influencing the intra-seasonal variations in winter temperatures. In terms of sea-level pressure fields, when the Mongolian high exhibits significant weakening after an initial strengthening in winter, P1 type temperature shifts are more likely to occur, and vice versa for P2 type shifts. Additionally, during these anomalous temperature shifts within the winter season, significant anomaly signals are observed in the North Atlantic, the equatorial central and eastern Pacific, and the equatorial Indian Ocean. High sea surface temperature anomalies in these three areas during the preceding summer and autumn seasons tend to lead to P1 type shifts in winter temperatures, whereas the opposite conditions tend to result in P2 type shifts, serving as potential precursors for prediction.
This study employs observational data from stations in the eastern part of the southwestern region and ERA5 reanalysis data to examine the characteristics and causes of the inverse phase shift anomalies in winter temperatures (hereafter referred to as anomalous shifts) in this area. The findings indicate that post-2000, this region tends to experience a pattern of colder temperatures earlier in the winter followed by warmer temperatures later (referred to as P1 type), whereas a pattern of warmer temperatures followed by colder ones (P2 type) was more prevalent in the 1970s. During the occurrence of these anomalous shifts in winter temperatures, the 500 hPa geopotential height field reveals that the Tibetan Plateau plays a crucial role in the circulation system, even surpassing the influence of the Ural blocking high. At the 200 hPa wind field level, systems such as the westerly jet stream affect the East Asian winter monsoon, thereby influencing the intra-seasonal variations in winter temperatures. In terms of sea-level pressure fields, when the Mongolian high exhibits significant weakening after an initial strengthening in winter, P1 type temperature shifts are more likely to occur, and vice versa for P2 type shifts. Additionally, during these anomalous temperature shifts within the winter season, significant anomaly signals are observed in the North Atlantic, the equatorial central and eastern Pacific, and the equatorial Indian Ocean. High sea surface temperature anomalies in these three areas during the preceding summer and autumn seasons tend to lead to P1 type shifts in winter temperatures, whereas the opposite conditions tend to result in P2 type shifts, serving as potential precursors for prediction.
Available online: March 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.121101
Abstract:
In order to reveal the weather causes of the rainstorm process that caused the flood in the Mintuo River and Jialing River basins, the rainfall and flood law of Yichang Control Station, and deepen the research on the occurrence and development mechanism of the flood in Yichang Station, based on the NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)reanalysis data and the conventional meteorological and hydrological observation data, the flood characteristics of 19 flood causing rainstorm processes that occurred in the Mintuo River and Jialing River basins from 1980 to 2020 were analyzed and studied using statistical and synoptic methods Flood causing rainstorm source, rain belt characteristics, topography and weather system configuration, etc. The results show that: (1) Before the continuous rainstorm process starts, the initial inflow flow of Yichang, the main control station in the Yangtze River basin, needs to reach about 19000m3 · s-1, and the average time from the beginning of the continuous rainstorm process of Mintuo River or Jialing River to the peak flood is about 6 days. The duration of rainstorm and cumulative area rainfall have a good correspondence with the flood peak. Each flood generating process requires at least one rainstorm of more than 3 days, most of which are 4-6 days. (2) The entire flood process occurred from July to September. Mid July to mid August is the main month in Yichang where peak type floods occur most frequently, with 62% of the daily average flow of over 50000 cubic meters per second occurring during this period. (3) The process of flood causing rainstorm is dominated by quasi-static rain belt, followed by easterly type and turning type. 85% of the process rain bands are distributed in a northeast southwest direction. The central source of heavy precipitation is closely related to special terrain, mainly distributed in three places: the intersection of the lower reaches of the Minjiang River and the Qingyi River, where turning precipitation mostly occurs; The middle and lower reaches of the Jialing River, the Fujiang River basin, and the Qujiang River basin are mostly of quasi static type; In the middle reaches of the Fujiang River and the northern part of the Qujiang River basin, the eastward moving rainstorm process often occurs here. (4) The precipitation process is divided into two categories: quasi stationary persistent precipitation and mobile persistent precipitation. There are three types of weather conceptual models that are prone to major floods: Type I is the edge of the subtropical high in the Western Pacific. The westerly short wave moves eastward to trigger the rainstorm type. The subtropical high generally presents a north-south meridional type, often blocking in eastern Sichuan, forming a situation of "low in the west and high in the east". The short-wave low value system moving southward and eastward is blocked in the Mintuo River basin by the subtropical high, which is stable and less dynamic, and produces more quasi-static rain belts; Type II is the rainstorm type triggered by the eastward movement of the low value system of the Qinghai Tibet Plateau. The subtropical high is mostly distributed in the latitudinal direction. The multi low value system of the plateau is active, and the shear line is mostly transverse. The vortex is often formed in the west of the shear line, moving eastward along the shear line, which is easy to form mobile precipitation; Type III is a low-level easterly flow rainstorm type, with few precipitation processes, mostly occurring in August. In the north, the continental high pressure or the Western Pacific subtropical high cooperate. The Mintuo River and Jialing River are affected by the northeast flow at the bottom of the low pressure, with weak cold air infiltration. The tropical low-pressure system in the south is blocked for a long time and moves steadily westward. A strong easterly flow is easy to form between the two. Combined with special terrain areas, continuous heavy precipitation is very easy to produce and strengthen. (5) Nearly 70% of the processes involve tropical low value systems or typhoons, among which the existence of the Bay of Bengal tropical depression system is crucial to the continuous rainstorm in the upstream. Not only does it bring enough energy and water vapor to the Mintuo River and Jialing River basins, but the involvement of water vapor on its eastern side can easily trigger low eddies in the Mintuo River and Jialing River basins, combined with special terrain, resulting in strong upward motion.
In order to reveal the weather causes of the rainstorm process that caused the flood in the Mintuo River and Jialing River basins, the rainfall and flood law of Yichang Control Station, and deepen the research on the occurrence and development mechanism of the flood in Yichang Station, based on the NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)reanalysis data and the conventional meteorological and hydrological observation data, the flood characteristics of 19 flood causing rainstorm processes that occurred in the Mintuo River and Jialing River basins from 1980 to 2020 were analyzed and studied using statistical and synoptic methods Flood causing rainstorm source, rain belt characteristics, topography and weather system configuration, etc. The results show that: (1) Before the continuous rainstorm process starts, the initial inflow flow of Yichang, the main control station in the Yangtze River basin, needs to reach about 19000m3 · s-1, and the average time from the beginning of the continuous rainstorm process of Mintuo River or Jialing River to the peak flood is about 6 days. The duration of rainstorm and cumulative area rainfall have a good correspondence with the flood peak. Each flood generating process requires at least one rainstorm of more than 3 days, most of which are 4-6 days. (2) The entire flood process occurred from July to September. Mid July to mid August is the main month in Yichang where peak type floods occur most frequently, with 62% of the daily average flow of over 50000 cubic meters per second occurring during this period. (3) The process of flood causing rainstorm is dominated by quasi-static rain belt, followed by easterly type and turning type. 85% of the process rain bands are distributed in a northeast southwest direction. The central source of heavy precipitation is closely related to special terrain, mainly distributed in three places: the intersection of the lower reaches of the Minjiang River and the Qingyi River, where turning precipitation mostly occurs; The middle and lower reaches of the Jialing River, the Fujiang River basin, and the Qujiang River basin are mostly of quasi static type; In the middle reaches of the Fujiang River and the northern part of the Qujiang River basin, the eastward moving rainstorm process often occurs here. (4) The precipitation process is divided into two categories: quasi stationary persistent precipitation and mobile persistent precipitation. There are three types of weather conceptual models that are prone to major floods: Type I is the edge of the subtropical high in the Western Pacific. The westerly short wave moves eastward to trigger the rainstorm type. The subtropical high generally presents a north-south meridional type, often blocking in eastern Sichuan, forming a situation of "low in the west and high in the east". The short-wave low value system moving southward and eastward is blocked in the Mintuo River basin by the subtropical high, which is stable and less dynamic, and produces more quasi-static rain belts; Type II is the rainstorm type triggered by the eastward movement of the low value system of the Qinghai Tibet Plateau. The subtropical high is mostly distributed in the latitudinal direction. The multi low value system of the plateau is active, and the shear line is mostly transverse. The vortex is often formed in the west of the shear line, moving eastward along the shear line, which is easy to form mobile precipitation; Type III is a low-level easterly flow rainstorm type, with few precipitation processes, mostly occurring in August. In the north, the continental high pressure or the Western Pacific subtropical high cooperate. The Mintuo River and Jialing River are affected by the northeast flow at the bottom of the low pressure, with weak cold air infiltration. The tropical low-pressure system in the south is blocked for a long time and moves steadily westward. A strong easterly flow is easy to form between the two. Combined with special terrain areas, continuous heavy precipitation is very easy to produce and strengthen. (5) Nearly 70% of the processes involve tropical low value systems or typhoons, among which the existence of the Bay of Bengal tropical depression system is crucial to the continuous rainstorm in the upstream. Not only does it bring enough energy and water vapor to the Mintuo River and Jialing River basins, but the involvement of water vapor on its eastern side can easily trigger low eddies in the Mintuo River and Jialing River basins, combined with special terrain, resulting in strong upward motion.
Available online: March 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.082101
Abstract:
Based on CMA best-track and ECMWF fine grid data, 16 variables during TC genesis were calculated. The stepwise regression algorithm of double test was used to select seven prediction factors with significance, and the TC genesis forecasting equation was established. The independent sample test results show that the hit rate of the wind speed predicted by the regression method is higher than that of the wind speed and pressure predicted by the numerical model. In 2022, the stepwise regression algorithm based on double testing was trialed in the TC genesis forecasting operation. The test results of generating forecast for typhoon 2203 " Chaba " show that the regression method has a good performance, which can provide a reference for forecasters to judge whether and when the typhoon is generated.
Based on CMA best-track and ECMWF fine grid data, 16 variables during TC genesis were calculated. The stepwise regression algorithm of double test was used to select seven prediction factors with significance, and the TC genesis forecasting equation was established. The independent sample test results show that the hit rate of the wind speed predicted by the regression method is higher than that of the wind speed and pressure predicted by the numerical model. In 2022, the stepwise regression algorithm based on double testing was trialed in the TC genesis forecasting operation. The test results of generating forecast for typhoon 2203 " Chaba " show that the regression method has a good performance, which can provide a reference for forecasters to judge whether and when the typhoon is generated.
Available online: February 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.071002
Abstract:
The severe convective rainstorm occurred at west side of Liupan Mountains on 15 July 2022 were analyzed based on the data from X-band dual polarization weather radar, C-band Doppler weather radar, wind profiler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that the rainstorm occurred in the northwest of the Western Pacific subtropical high. The main area of heavy rainfall is the south side of the low-level shear line and the left front side of the low-level jet. Affected by the Liupan mountain terrain, the mesoscale ground convergence line, mesoscale low-level southwest jet and mesoscale eddy might be important systems of triggering, maintaining and enhancing of the process. The rainstorm was caused by two mesoscale echo bands, the convective cells on them propagated backward, and the train effect was obvious. The strengthening of low-level jet, the increasing of vertical wind shear, the downward disturbance of wind speed, and the dry intrusion appeared 1~2 hours ahead of the increase of precipitation in five minutes, which had a certain reference value for rainstorm forecast and early warning. The center of heavy rainfall had a better corresponding relationship with the echo area with intensity ≥50 dBz and the large value area of vertical integrated liquid water, echo tops, the large range of differential phase shift (KDP) and differential reflectivity (ZDR). KDP was a good indicator for intensity of heavy rainfall. The maximum value of KDP and ZDR appeared 10 minutes earlier than the maximum rainfall in five minutes. The ZDR arc and ZDR column also appeared 10~20 minutes earlier than the maximum rainfall. During the strongest rainfall period, the KDP was 3.0~4.0 °·km-1, the ZDR was 3.0~3.3 dB, and the correlation coefficient was 0.90~0.95. This suggested that the spectrum of rain particulates contained a large amount of relatively large-sized raindrops, increasing the extremes of precipitation.
The severe convective rainstorm occurred at west side of Liupan Mountains on 15 July 2022 were analyzed based on the data from X-band dual polarization weather radar, C-band Doppler weather radar, wind profiler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that the rainstorm occurred in the northwest of the Western Pacific subtropical high. The main area of heavy rainfall is the south side of the low-level shear line and the left front side of the low-level jet. Affected by the Liupan mountain terrain, the mesoscale ground convergence line, mesoscale low-level southwest jet and mesoscale eddy might be important systems of triggering, maintaining and enhancing of the process. The rainstorm was caused by two mesoscale echo bands, the convective cells on them propagated backward, and the train effect was obvious. The strengthening of low-level jet, the increasing of vertical wind shear, the downward disturbance of wind speed, and the dry intrusion appeared 1~2 hours ahead of the increase of precipitation in five minutes, which had a certain reference value for rainstorm forecast and early warning. The center of heavy rainfall had a better corresponding relationship with the echo area with intensity ≥50 dBz and the large value area of vertical integrated liquid water, echo tops, the large range of differential phase shift (KDP) and differential reflectivity (ZDR). KDP was a good indicator for intensity of heavy rainfall. The maximum value of KDP and ZDR appeared 10 minutes earlier than the maximum rainfall in five minutes. The ZDR arc and ZDR column also appeared 10~20 minutes earlier than the maximum rainfall. During the strongest rainfall period, the KDP was 3.0~4.0 °·km-1, the ZDR was 3.0~3.3 dB, and the correlation coefficient was 0.90~0.95. This suggested that the spectrum of rain particulates contained a large amount of relatively large-sized raindrops, increasing the extremes of precipitation.
Available online: January 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.011801
Abstract:
A large-scale convective gale event was studied based on conventional observation data, automatic weather station data, GFS analysis data at spatial resolution of 0.25°and temporal of 6h, observations of Doppler radar , and Fengyun-4 satellite data in East China on 12 April 2020 under the background of consistent northwesterly air flow from the lower to the middle layer behind the North China Cold Vortex. The results demonstrate that after the strong cold air gales moved southward on the morning of the 12th, a convective storm was triggered near the drylines at the junction of Shandong and Jiangsu province on the afternoon in the favorable thermal background of cold advection at the middle level and warm advection at the lower level, the convective storm occurred in the area with a large temperature difference between 500hPa and 850hPa and the initial shape of the convective cloud matches the dryline well;The convective system was strengthened under favorable conditions such as better water vapor condition, stronger wind speed in the middle layer, merged of gust front and the influence of the special land and sea distribution in Hangzhou Bay, which caused the large-scale convective gale weather in Jiangsu, southeast Anhui and north Zhejiang again, and 13 extreme gales occured near the Zhoushan Islands ; The 13 extreme gales occurred at the fracture area of echo and theγ scale mesoscale vortices, which caused by the radiation of rear inflow jet and the strong downdraft, smooth underlying surface, fast-moving convection system and small-scale downburst currents within the system.
A large-scale convective gale event was studied based on conventional observation data, automatic weather station data, GFS analysis data at spatial resolution of 0.25°and temporal of 6h, observations of Doppler radar , and Fengyun-4 satellite data in East China on 12 April 2020 under the background of consistent northwesterly air flow from the lower to the middle layer behind the North China Cold Vortex. The results demonstrate that after the strong cold air gales moved southward on the morning of the 12th, a convective storm was triggered near the drylines at the junction of Shandong and Jiangsu province on the afternoon in the favorable thermal background of cold advection at the middle level and warm advection at the lower level, the convective storm occurred in the area with a large temperature difference between 500hPa and 850hPa and the initial shape of the convective cloud matches the dryline well;The convective system was strengthened under favorable conditions such as better water vapor condition, stronger wind speed in the middle layer, merged of gust front and the influence of the special land and sea distribution in Hangzhou Bay, which caused the large-scale convective gale weather in Jiangsu, southeast Anhui and north Zhejiang again, and 13 extreme gales occured near the Zhoushan Islands ; The 13 extreme gales occurred at the fracture area of echo and theγ scale mesoscale vortices, which caused by the radiation of rear inflow jet and the strong downdraft, smooth underlying surface, fast-moving convection system and small-scale downburst currents within the system.
Available online: January 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.012301
Abstract:
Based on the hourly rainfall data of 2066 automatic weather stations and rainstorm disaster information in Chongqing from 2011 to 2021, the slide sampling of rainstorm process and the percentile method are used to determine the rainstorm warning signal standards for counties and the disaster risk warning grades for the whole city, which can provide reference for Chongqing local departments to initiate rainstorm emergency response. The main conclusions are as follows: (1) a total of 5363 rainstorm processes occurred in 34 counties with meteorological authorities in Chongqing, with an average of 14.3 times per year in each county and 1h, 3h and 12h are selected as the reference duration for issuing rainstorm process warning signals. (2) Rainstorm warning signal (blue, yellow, orange, and red) standard thresholds of different durations are obtained by taking 30~50%, 70~80%, 90~95%, and 99~99.9% precipitation levels and adjusting according to the actual application, which are as follows: 1h-30-50-70-100 mm, 3h-50-70-100-150 mm, 12h-70-100-150-250 mm. The issuance of warning signals for counties adopts the highest level of different durations. (3) The probability of disaster caused by different warning signals increases both with signal strength and duration, warning signals of blue, yellow, orange, red for each county have an average of 5.4, 4.0, 1.3, 0.18 times per year according to the highest warning level of different durations and each signal takes from maximum disaster probability of different durations as 30%, 60%, 85%, and 95% respectively. (4) A total of 114 regional rainstorm processes occurred in the city, and rainstorm disaster risk warning levels determined by the number of possible disaster counties issue an average of 5.3 (IV), 3.1 (III), 1.6 (II), 0.1 (I) times per year, which is basically consistent with the frequency of counties and conforms to the regularity of warning releases. Key words: rainstorm warning signals; slide sampling during rainstorm process; percentile method; probability of disaster; rainstorm disaster warning.
Based on the hourly rainfall data of 2066 automatic weather stations and rainstorm disaster information in Chongqing from 2011 to 2021, the slide sampling of rainstorm process and the percentile method are used to determine the rainstorm warning signal standards for counties and the disaster risk warning grades for the whole city, which can provide reference for Chongqing local departments to initiate rainstorm emergency response. The main conclusions are as follows: (1) a total of 5363 rainstorm processes occurred in 34 counties with meteorological authorities in Chongqing, with an average of 14.3 times per year in each county and 1h, 3h and 12h are selected as the reference duration for issuing rainstorm process warning signals. (2) Rainstorm warning signal (blue, yellow, orange, and red) standard thresholds of different durations are obtained by taking 30~50%, 70~80%, 90~95%, and 99~99.9% precipitation levels and adjusting according to the actual application, which are as follows: 1h-30-50-70-100 mm, 3h-50-70-100-150 mm, 12h-70-100-150-250 mm. The issuance of warning signals for counties adopts the highest level of different durations. (3) The probability of disaster caused by different warning signals increases both with signal strength and duration, warning signals of blue, yellow, orange, red for each county have an average of 5.4, 4.0, 1.3, 0.18 times per year according to the highest warning level of different durations and each signal takes from maximum disaster probability of different durations as 30%, 60%, 85%, and 95% respectively. (4) A total of 114 regional rainstorm processes occurred in the city, and rainstorm disaster risk warning levels determined by the number of possible disaster counties issue an average of 5.3 (IV), 3.1 (III), 1.6 (II), 0.1 (I) times per year, which is basically consistent with the frequency of counties and conforms to the regularity of warning releases. Key words: rainstorm warning signals; slide sampling during rainstorm process; percentile method; probability of disaster; rainstorm disaster warning.
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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.
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.
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.
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.
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.
2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.01.001
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.
2012,38(10):1255-1266, DOI: 10.7519/j.issn.1000-0526.2012.10.012
Abstract:
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
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.
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.
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.
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.
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