ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,Issue 9,2024 Table of Contents
2024, 50(9):1033-1042.
DOI: 10.7519/j.issn.1000-0526.2024.080902
Abstract:
During mid and late February of 2024, a strong cold surge, dust storm and various freezing weathers (snowstorm, sleet, freezing rain, rainstorm and severe convection producing large hail and damaging gust), associated with severe convection to the south, occurred in a large area over China. Multiple high-impact-weather events showed up during this extreme complicated process. In order to provide an introduction for the subsequent detailed and in-depth analysis and research of this process, in this article we discuss briefly the mechanisms and forecasting challenges of these high-impact-weather events, without exploration in details and in depth.
During mid and late February of 2024, a strong cold surge, dust storm and various freezing weathers (snowstorm, sleet, freezing rain, rainstorm and severe convection producing large hail and damaging gust), associated with severe convection to the south, occurred in a large area over China. Multiple high-impact-weather events showed up during this extreme complicated process. In order to provide an introduction for the subsequent detailed and in-depth analysis and research of this process, in this article we discuss briefly the mechanisms and forecasting challenges of these high-impact-weather events, without exploration in details and in depth.
2024, 50(9):1043-1056.
DOI: 10.7519/j.issn.1000-0526.2024.042401
Abstract:
FY-3D Vertical Atmospheric Sounding System (VASS) temperature and humidity profile products are evaluated using radiosonde observations and ERA5 reanalysis dataset in Sichuan Basin and Western Sichuan Plateau. The results show that relative to ERA5 data, the average bias of FY-3D/VASS temperature in different seasons is from -0.631 to 0.500℃ and from -2.230 to -1.234℃ respectively, and the root mean square error is from 2.117 to 3.222℃ and from 3.077 to 3.460℃ in the basin and the plateau area respectively. Vertically, the accuracy of temperature is low at 800-700 hPa in the basin area and gradually decreases as the height decreases in the plateau area. The average bias of FY-3D/VASS specific humidity relative to ERA5 data is generally negative, while the average bias in different seasons is from -0.775 to -0.525 g·kg-1 and from -1.096 to -0.347 g·kg-1 respectively, and the root mean square error is from 1.251 to 2.367 g·kg-1 and from 0.696 to 1.991 g·kg-1 at the basin and the plateau area respectively. The accuracy of specific humidity is relatively low at 700-600 hPa. In consideration of the small diurnal difference in the accuracy of FY-3D/VASS temperature and humidity, the average biases of the two groups of evaluations are properly added. As a result, the average biases of FY-3D/VASS temperature and specific humidity can be indirectly obtained based on the radiosonde observations. Relative to radiosonde observations, the average bias of FY-3D/VASS temperature in the basin area is relatively small and the average bias in the plateau area is lower by about 2.440℃. The average bias of FY-3D/VASS specific humidity in the basin and plateau area is lower by about 0.612 g·kg-1. The above-mentioned results are significant for improving the weather and climate application ability of FY-3D/VASS temperature and humidity profile products in Sichuan Basin and Western Sichuan Plateau.
FY-3D Vertical Atmospheric Sounding System (VASS) temperature and humidity profile products are evaluated using radiosonde observations and ERA5 reanalysis dataset in Sichuan Basin and Western Sichuan Plateau. The results show that relative to ERA5 data, the average bias of FY-3D/VASS temperature in different seasons is from -0.631 to 0.500℃ and from -2.230 to -1.234℃ respectively, and the root mean square error is from 2.117 to 3.222℃ and from 3.077 to 3.460℃ in the basin and the plateau area respectively. Vertically, the accuracy of temperature is low at 800-700 hPa in the basin area and gradually decreases as the height decreases in the plateau area. The average bias of FY-3D/VASS specific humidity relative to ERA5 data is generally negative, while the average bias in different seasons is from -0.775 to -0.525 g·kg-1 and from -1.096 to -0.347 g·kg-1 respectively, and the root mean square error is from 1.251 to 2.367 g·kg-1 and from 0.696 to 1.991 g·kg-1 at the basin and the plateau area respectively. The accuracy of specific humidity is relatively low at 700-600 hPa. In consideration of the small diurnal difference in the accuracy of FY-3D/VASS temperature and humidity, the average biases of the two groups of evaluations are properly added. As a result, the average biases of FY-3D/VASS temperature and specific humidity can be indirectly obtained based on the radiosonde observations. Relative to radiosonde observations, the average bias of FY-3D/VASS temperature in the basin area is relatively small and the average bias in the plateau area is lower by about 2.440℃. The average bias of FY-3D/VASS specific humidity in the basin and plateau area is lower by about 0.612 g·kg-1. The above-mentioned results are significant for improving the weather and climate application ability of FY-3D/VASS temperature and humidity profile products in Sichuan Basin and Western Sichuan Plateau.
2024, 50(9):1057-1070.
DOI: 10.7519/j.issn.1000-0526.2024.063001
Abstract:
Cloud is one of the most important and active factors in weather and climate, and plays an important role in modulating the radiation-energy balance and water cycle of atmospheric system. The effective forecast of total cloud cover can lay a basis for better grasp of weather phenomena and prediction of new energy output such as photovoltaic power generation. The model CMA-BJ (Beijing Rapid Update Cycle System) can provide hourly high-resolution total cloud cover prediction products. In this paper, the prediction performance of CMA-BJ is systematically examined and evaluated by the time scale separation method, and the error sources are analyzed, so as to provide a reference for product interpretation and model improvement. The results show that the spatial distribution characteristics and diurnal variation intensity of total cloud cover can be well predicted by CMA-BJ. The pattern correlation coefficients between the CMA-BJ forecasted and observed total cloud cover with 1-24 h lead time are all greater than 0.6 in each month. However, the total cloud cover and diurnal variation intensity are significantly underestimated in winter (January), with the deviation of CMA-BJ reaching -0.133. As the forecasting time increases, the prediction ability of CMA-BJ decreases, with the averaged TCC skills being 0.470, 0.409, 0.355 and 0.315 for the 1-4 d forecast, which means the skillful prediction can be maintained up to 48-72 hours. The diagnostic analysis shows that the low relative humidity in the model may largely contribute to the negative deviation in total cloud cover prediction. Besides, the bias of vertical velocity prediction is also an important reason for the cloud cover prediction error.
Cloud is one of the most important and active factors in weather and climate, and plays an important role in modulating the radiation-energy balance and water cycle of atmospheric system. The effective forecast of total cloud cover can lay a basis for better grasp of weather phenomena and prediction of new energy output such as photovoltaic power generation. The model CMA-BJ (Beijing Rapid Update Cycle System) can provide hourly high-resolution total cloud cover prediction products. In this paper, the prediction performance of CMA-BJ is systematically examined and evaluated by the time scale separation method, and the error sources are analyzed, so as to provide a reference for product interpretation and model improvement. The results show that the spatial distribution characteristics and diurnal variation intensity of total cloud cover can be well predicted by CMA-BJ. The pattern correlation coefficients between the CMA-BJ forecasted and observed total cloud cover with 1-24 h lead time are all greater than 0.6 in each month. However, the total cloud cover and diurnal variation intensity are significantly underestimated in winter (January), with the deviation of CMA-BJ reaching -0.133. As the forecasting time increases, the prediction ability of CMA-BJ decreases, with the averaged TCC skills being 0.470, 0.409, 0.355 and 0.315 for the 1-4 d forecast, which means the skillful prediction can be maintained up to 48-72 hours. The diagnostic analysis shows that the low relative humidity in the model may largely contribute to the negative deviation in total cloud cover prediction. Besides, the bias of vertical velocity prediction is also an important reason for the cloud cover prediction error.
2024, 50(9):1071-1080.
DOI: 10.7519/j.issn.1000-0526.2024.051301
Abstract:
Due to the unique geographical location of the Beijing-Tianjin-Hebei Region, topography and mesoscale weather play a crucial role in the formation of regional air pollution in this region. A typical air pollution process was observed in the region from 29 to 30 December 2023. To explore the causes and deep formation mechanism for this pollution process, the influences of mesoscale weather and boundary layer structure on the intensification of heavy pollution under the warm front and special terrain background are studied on the basis of the numerical simulation of RMAPS-CHEM system, the PM2.5 concentration observation and the meteorological data. It is found that under the influence of North China topographic trough, the southwest wind not only transported the pollutants, but also brought the warm and humid air mass from south to north, resulting in the formation of an obvious low-level warm front on the southeast side of the Beijing-Tianjin-Hebei Plain. Synergistically, impacted by warm front and topographic thermal characteristics, the polluted cold air mass was driven by warm front in the southeast side and restricted by terrain in the northwest side, forming accumulation called cold pool near the surface of the plain area close to the mountains. The strong stable atmospheric condition of the temperature inversion in the cold pool, calm wind and extremely low boundary layer height led to the pollutants to be trapped in a limited vertical space. At the same time, the weak wind caused the stagnation of air mass and inhibited the horizontal transmission and diffusion of pollutants. These adverse factors ultimately resulted in the continuous accumulation of pollutant concentrations.
Due to the unique geographical location of the Beijing-Tianjin-Hebei Region, topography and mesoscale weather play a crucial role in the formation of regional air pollution in this region. A typical air pollution process was observed in the region from 29 to 30 December 2023. To explore the causes and deep formation mechanism for this pollution process, the influences of mesoscale weather and boundary layer structure on the intensification of heavy pollution under the warm front and special terrain background are studied on the basis of the numerical simulation of RMAPS-CHEM system, the PM2.5 concentration observation and the meteorological data. It is found that under the influence of North China topographic trough, the southwest wind not only transported the pollutants, but also brought the warm and humid air mass from south to north, resulting in the formation of an obvious low-level warm front on the southeast side of the Beijing-Tianjin-Hebei Plain. Synergistically, impacted by warm front and topographic thermal characteristics, the polluted cold air mass was driven by warm front in the southeast side and restricted by terrain in the northwest side, forming accumulation called cold pool near the surface of the plain area close to the mountains. The strong stable atmospheric condition of the temperature inversion in the cold pool, calm wind and extremely low boundary layer height led to the pollutants to be trapped in a limited vertical space. At the same time, the weak wind caused the stagnation of air mass and inhibited the horizontal transmission and diffusion of pollutants. These adverse factors ultimately resulted in the continuous accumulation of pollutant concentrations.
2024, 50(9):1081-1092.
DOI: 10.7519/j.issn.1000-0526.2024.031403
Abstract:
Based on hourly precipitation data from the National Meteorological Information Centre of CMA, combined with the diversity of the terrain, the temporal and spatial characteristics of hourly precipitation, as well as characteristics of different types of heavy rainfall event (HRE) before (1992-2002) and after (2003-2021) the impoundment in the Three Gorges Reservoir Area in summer (June-August) are analyzed. The results are as follows. After impoundment, the precipitation and frequency decrease but intensity increases. There is an obvious geographical distribution pattern of precipitation changes, with precipitation, frequency and intensity increasing in the north central part of the Three Gorges Reservoir Area, mostly located in the area north of the Yangtze River, and the precipitation and frequency decrease in the southwest and the intensity weakens in the south central part and northwest of the Three Gorges Reservoir Area, mostly located to the south of 31°N. The spatial difference degree of diurnal peak phases of hourly precipitation before and after impoundment is precipitation intensity>precipitation>precipitation frequency. After impoundment, the stations with increasing trend of precipitation, frequency and intensity become more, and the diurnal peak phases of precipitation and intensity have the feature of phase advance in high altitude mountainous areas. There is no significant change in the precipitation probability and proportion of hourly precipitation at various grades before and after impoundment. The precipitation probability is the maximum at the grade of ［0.1, 0.5） mm, and the minimum at the grade of ≥20 mm. The precipitation proportion shows the maximum at the grade of ［1, 5） mm, the minimum at the grade of ［0.1, 0.5） mm, and about 15% at the grade of ≥20 mm. The diurnal 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, and the diurnal scale fluctuations of hourly precipitation intensity at each grade are more frequent. Analysis of different duration types of HRE shows that before and after impoundment, the short-duration type of HRE is the highest and the long-duration type is the lowest. The short-duration type of HRE mostly starts in the afternoon, while medium-duration and long-duration types of HRE mostly start at night. After impoundment, the condition is beneficial for HRE maintenance. The probability of short-duration type of HRE starting at noon and in the afternoon increases, and the probability of medium-duration and long-duration types of HRE starting in the morning increase.
Based on hourly precipitation data from the National Meteorological Information Centre of CMA, combined with the diversity of the terrain, the temporal and spatial characteristics of hourly precipitation, as well as characteristics of different types of heavy rainfall event (HRE) before (1992-2002) and after (2003-2021) the impoundment in the Three Gorges Reservoir Area in summer (June-August) are analyzed. The results are as follows. After impoundment, the precipitation and frequency decrease but intensity increases. There is an obvious geographical distribution pattern of precipitation changes, with precipitation, frequency and intensity increasing in the north central part of the Three Gorges Reservoir Area, mostly located in the area north of the Yangtze River, and the precipitation and frequency decrease in the southwest and the intensity weakens in the south central part and northwest of the Three Gorges Reservoir Area, mostly located to the south of 31°N. The spatial difference degree of diurnal peak phases of hourly precipitation before and after impoundment is precipitation intensity>precipitation>precipitation frequency. After impoundment, the stations with increasing trend of precipitation, frequency and intensity become more, and the diurnal peak phases of precipitation and intensity have the feature of phase advance in high altitude mountainous areas. There is no significant change in the precipitation probability and proportion of hourly precipitation at various grades before and after impoundment. The precipitation probability is the maximum at the grade of ［0.1, 0.5） mm, and the minimum at the grade of ≥20 mm. The precipitation proportion shows the maximum at the grade of ［1, 5） mm, the minimum at the grade of ［0.1, 0.5） mm, and about 15% at the grade of ≥20 mm. The diurnal 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, and the diurnal scale fluctuations of hourly precipitation intensity at each grade are more frequent. Analysis of different duration types of HRE shows that before and after impoundment, the short-duration type of HRE is the highest and the long-duration type is the lowest. The short-duration type of HRE mostly starts in the afternoon, while medium-duration and long-duration types of HRE mostly start at night. After impoundment, the condition is beneficial for HRE maintenance. The probability of short-duration type of HRE starting at noon and in the afternoon increases, and the probability of medium-duration and long-duration types of HRE starting in the morning increase.
2024, 50(9):1093-1104.
DOI: 10.7519/j.issn.1000-0526.2024.051601
Abstract:
Based on the high spatio-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, we comparatively analyze 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 was no obvious synoptic scale system dominating the three local sudden heavy rainstorms, but the ambient atmosphere had high convective available potential energy and low convective inhibition energy. The lifting condensation height was only 0.2-0.4 km, with a certain wet layer in the lower level. Generally, the occurrence of local sudden rainstorm is mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the three local sudden rainstorms, the differences in temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious nonuniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of the local convection. In addition, before the occurrence of the local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened. The converged thermal low pressure of the urban heat island and the converged sea breeze jointly made the mesoscale convergence intensity significantly strengthened, which was the main cause for the occurrence of local sudden rainstorm. The meso-γ scale convective cells were triggered at the edge of the strong convergence center.
Based on the high spatio-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, we comparatively analyze 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 was no obvious synoptic scale system dominating the three local sudden heavy rainstorms, but the ambient atmosphere had high convective available potential energy and low convective inhibition energy. The lifting condensation height was only 0.2-0.4 km, with a certain wet layer in the lower level. Generally, the occurrence of local sudden rainstorm is mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the three local sudden rainstorms, the differences in temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious nonuniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of the local convection. In addition, before the occurrence of the local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened. The converged thermal low pressure of the urban heat island and the converged sea breeze jointly made the mesoscale convergence intensity significantly strengthened, which was the main cause for the occurrence of local sudden rainstorm. The meso-γ scale convective cells were triggered at the edge of the strong convergence center.
2024, 50(9):1105-1119.
DOI: 10.7519/j.issn.1000-0526.2024.071202
Abstract:
Based on conventional observation, three-dimensional lightning locator, Doppler weather radar and ERA5 reanalysis data, the characteristics of a convective event on 14 December 2023 in Shandong Province are analyzed. The position of the ground cold front is determined by using the frontogenesis function, the dense zone of pseudo-equivalent temperature, and the temperature variation. A conceptual model diagram of the physical process is proposed. The results show that thunderstorm and heavy snowfall occurred at the rear of the ground cold front, with a deep and stable cold cushion in the low altitude, and strong warm and humid air above the temperature inversion layer, forming the environment for elevated thunderstorm. During the blizzard, there was convective-symmetric instability, and the symmetric instability and potential instability were at different levels. The symmetric instability was below 700 hPa, and the tilting convection developed during the forced uplift of warm and humid air flow along the low-level cold cushion. The potential instability was located at 700-500 hPa and was established with the advancement of the southwest jet. When the tilting convection caused by symmetric instability reached a level of 700-500 hPa, the energy of potential instability was released, leading to the development of deep and strong vertical convection. The establishment of potential instability was consistent with the northward advance of 20 m·s-1 wind speed at 700-500 hPa, which was 1-2 h ahead of the heaviest snowfall and thunder. The triggering of elevated thunderstorm was not only related to the uplift of the low-level cold cushion, but also to the enhancement of wind near 700-500 hPa in the middle layer. With the increase of wind speed at 700-500 hPa, the positive vorticity advection was strengthened, and then the upward airflow further developed, causing severe snowfall and high-frequency lightning. The convective property of this elevated convection was not typical and the echo intensity was mainly concentrated in 20-35 dBz, but the echo top height exceeded the -30℃ layer height and the 35 dBz echo extended above the -10℃ layer height. Therefore, it is still necessary to pay close attention to the occurrence of lightning in winter.
Based on conventional observation, three-dimensional lightning locator, Doppler weather radar and ERA5 reanalysis data, the characteristics of a convective event on 14 December 2023 in Shandong Province are analyzed. The position of the ground cold front is determined by using the frontogenesis function, the dense zone of pseudo-equivalent temperature, and the temperature variation. A conceptual model diagram of the physical process is proposed. The results show that thunderstorm and heavy snowfall occurred at the rear of the ground cold front, with a deep and stable cold cushion in the low altitude, and strong warm and humid air above the temperature inversion layer, forming the environment for elevated thunderstorm. During the blizzard, there was convective-symmetric instability, and the symmetric instability and potential instability were at different levels. The symmetric instability was below 700 hPa, and the tilting convection developed during the forced uplift of warm and humid air flow along the low-level cold cushion. The potential instability was located at 700-500 hPa and was established with the advancement of the southwest jet. When the tilting convection caused by symmetric instability reached a level of 700-500 hPa, the energy of potential instability was released, leading to the development of deep and strong vertical convection. The establishment of potential instability was consistent with the northward advance of 20 m·s-1 wind speed at 700-500 hPa, which was 1-2 h ahead of the heaviest snowfall and thunder. The triggering of elevated thunderstorm was not only related to the uplift of the low-level cold cushion, but also to the enhancement of wind near 700-500 hPa in the middle layer. With the increase of wind speed at 700-500 hPa, the positive vorticity advection was strengthened, and then the upward airflow further developed, causing severe snowfall and high-frequency lightning. The convective property of this elevated convection was not typical and the echo intensity was mainly concentrated in 20-35 dBz, but the echo top height exceeded the -30℃ layer height and the 35 dBz echo extended above the -10℃ layer height. Therefore, it is still necessary to pay close attention to the occurrence of lightning in winter.
2024, 50(9):1120-1128.
DOI: 10.7519/j.issn.1000-0526.2024.071601
Abstract:
Using hourly ERA5 reanalysis data and observation data, the characteristics of mesoscale vortices during the extreme rain and snow event in North China from 13 to 14 February 2020 are analyzed. Besides, the development mechanism of the mesoscale vortices is diagnosed by the circulation integral equation of relative vorticity. The results show that the average vorticity vertical profile of the mesoscale vortex activity area (referred to as the vortex zone) exhibits an “S” shaped distribution, with extreme positive and negative vorticity values at 800 hPa and 400 hPa, respectively. The average vorticity intensity from 900 hPa to 700 hPa varies in the same phases with the precipitation intensity in the plain area. The peak of vortex intensity is about two hours earlier than the peak of precipitation intensity, and the correlation coefficient between the two is 0.76, suggesting that the intensity of lower-level vorticity has indicative significance for snowfall forecasting. From the perspective of the dynamical mechanisms driving vortex development, the positive vorticity below 800 hPa in the vortex zone mainly originates from horizontal wind convergence. The upward motion from 800 hPa to 700 hPa and the clockwise rotation of wind with increasing altitude contribute more to vorticity. Compared to the snowfall process without mesoscale vortex on 14 February 2019, the structure of vorticity in the vertical direction has no “S” shape, and the intensity of vorticity in the middle and lower layers is weak, resulting in obviously lower snowfall amount over Beijing.The existence or absence of mesoscale vortex development in the vortex zone has indicative significance for predicting winter snowfall magnitude and extremity in Beijing.
Using hourly ERA5 reanalysis data and observation data, the characteristics of mesoscale vortices during the extreme rain and snow event in North China from 13 to 14 February 2020 are analyzed. Besides, the development mechanism of the mesoscale vortices is diagnosed by the circulation integral equation of relative vorticity. The results show that the average vorticity vertical profile of the mesoscale vortex activity area (referred to as the vortex zone) exhibits an “S” shaped distribution, with extreme positive and negative vorticity values at 800 hPa and 400 hPa, respectively. The average vorticity intensity from 900 hPa to 700 hPa varies in the same phases with the precipitation intensity in the plain area. The peak of vortex intensity is about two hours earlier than the peak of precipitation intensity, and the correlation coefficient between the two is 0.76, suggesting that the intensity of lower-level vorticity has indicative significance for snowfall forecasting. From the perspective of the dynamical mechanisms driving vortex development, the positive vorticity below 800 hPa in the vortex zone mainly originates from horizontal wind convergence. The upward motion from 800 hPa to 700 hPa and the clockwise rotation of wind with increasing altitude contribute more to vorticity. Compared to the snowfall process without mesoscale vortex on 14 February 2019, the structure of vorticity in the vertical direction has no “S” shape, and the intensity of vorticity in the middle and lower layers is weak, resulting in obviously lower snowfall amount over Beijing.The existence or absence of mesoscale vortex development in the vortex zone has indicative significance for predicting winter snowfall magnitude and extremity in Beijing.
2024, 50(9):1129-1141.
DOI: 10.7519/j.issn.1000-0526.2023.092802
Abstract:
In order to investigate microphysical characteristics in hailstorm, this paper uses the dual-polarization radar and raindrop spectrum data, as well as the hydrometer classification algorithm to analyze a hail event that occurred in Mount Taishan on 1 June 2020. The distribution features of radar variables, hydrometer and the raindrops in the region around the Mount Taishan Station are obtained when the hailstorm cloud passes through the Mount Taishan. The results show that when the front edge of hailstorm began to affect the Mount Taishan Station, the large gradient area of reflectivity (ZH) was next to the Mount Taishan Station coinciding with differential reflectivity (ZDR) arc position. The particles identified in ZDR arc were mainly composed of abundant big raindrops, which were formed by melting graupel particles over Mount Taishan Station. The structure of the raindrop spectrum was double-peak, and the greater contribution to precipitation was from 2-3 mm particles. When the main body of the hailstorm cloud influenced the Mount Taishan 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 Taishan Station, there was the bounded weak echo region (BWER), where the convergent ascending motion was enhanced. The BWER was semi-surrounded by the large value of ZDR (ZDR ring), and the particles in ZDR ring were mainly identified as big drops and hail, mixed with small amount of graupel and wet snow. The contoured frequency by altitude diagram (CFAD) shows that the ice phase process was enhanced. The hail particles under the -10℃ were mainly formed by the graupel particles between -10℃ layer and 0℃ layer riming the big drops 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 most contribution to precipitation was made by 14-16 mm particles. When the hailstorm cloud left the Mount Taishan Station, CFAD shows the ZH corresponding to the high frequency region decreased, the ice phase process was weaken, and the efficiency of the cold cloud droplets attached to the ice crystals to convert into graupel was reduced. A large number of ice crystals and dry snow particles were identified above Mount Taishan Station, where the feature of the stratiform cloud precipitation appeared. The structure of the raindrop spectrum became double-peak again， and the second peak value of particles was 2-3 mm, which contributed more to the precipitation.
In order to investigate microphysical characteristics in hailstorm, this paper uses the dual-polarization radar and raindrop spectrum data, as well as the hydrometer classification algorithm to analyze a hail event that occurred in Mount Taishan on 1 June 2020. The distribution features of radar variables, hydrometer and the raindrops in the region around the Mount Taishan Station are obtained when the hailstorm cloud passes through the Mount Taishan. The results show that when the front edge of hailstorm began to affect the Mount Taishan Station, the large gradient area of reflectivity (ZH) was next to the Mount Taishan Station coinciding with differential reflectivity (ZDR) arc position. The particles identified in ZDR arc were mainly composed of abundant big raindrops, which were formed by melting graupel particles over Mount Taishan Station. The structure of the raindrop spectrum was double-peak, and the greater contribution to precipitation was from 2-3 mm particles. When the main body of the hailstorm cloud influenced the Mount Taishan 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 Taishan Station, there was the bounded weak echo region (BWER), where the convergent ascending motion was enhanced. The BWER was semi-surrounded by the large value of ZDR (ZDR ring), and the particles in ZDR ring were mainly identified as big drops and hail, mixed with small amount of graupel and wet snow. The contoured frequency by altitude diagram (CFAD) shows that the ice phase process was enhanced. The hail particles under the -10℃ were mainly formed by the graupel particles between -10℃ layer and 0℃ layer riming the big drops 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 most contribution to precipitation was made by 14-16 mm particles. When the hailstorm cloud left the Mount Taishan Station, CFAD shows the ZH corresponding to the high frequency region decreased, the ice phase process was weaken, and the efficiency of the cold cloud droplets attached to the ice crystals to convert into graupel was reduced. A large number of ice crystals and dry snow particles were identified above Mount Taishan Station, where the feature of the stratiform cloud precipitation appeared. The structure of the raindrop spectrum became double-peak again， and the second peak value of particles was 2-3 mm, which contributed more to the precipitation.
2024, 50(9):1142-1152.
DOI: 10.7519/j.issn.1000-0526.2024.071201
Abstract:
We use Baodi S-Band Dual-Polarization Weather Radar data from June 2022 to March 2023 in analyzing the biological activity in the sky over Tianjin Region. The results show that there are obvious seasonal and diurnal variations of biological activities in the sky over Tianjin Region. The migration echoes of migratory birds detected by radar are concentrated from late February to late November, during which wetland bird activity is more obvious in summer, and migratory bird activity is particularly frequent in February and November. The appearence time of bird echo is obviously correlated to sunrise and sunset. The echoes of birds show obvious circular characteristics in the reflectivity products, with the echo inten-sity exceeding 35 dBz. It can be seen from the radial velocity product that the flight speed of birds is about 10-27 m·s-1; and from the product of correlation coefficient (CC) that the overall CC of bird echo is low, mainly distributed in the range of 0.1-0.8. And then from the differential reflectivity （ZDR） products, we can see that the distribution of ZDR is not uniform, up to 3-5 dB as the highest. Compared to single polarization weather radar, S-band dual-polarization weather radar has significant advantages in recognizing biological echoes in the sky.
We use Baodi S-Band Dual-Polarization Weather Radar data from June 2022 to March 2023 in analyzing the biological activity in the sky over Tianjin Region. The results show that there are obvious seasonal and diurnal variations of biological activities in the sky over Tianjin Region. The migration echoes of migratory birds detected by radar are concentrated from late February to late November, during which wetland bird activity is more obvious in summer, and migratory bird activity is particularly frequent in February and November. The appearence time of bird echo is obviously correlated to sunrise and sunset. The echoes of birds show obvious circular characteristics in the reflectivity products, with the echo inten-sity exceeding 35 dBz. It can be seen from the radial velocity product that the flight speed of birds is about 10-27 m·s-1; and from the product of correlation coefficient (CC) that the overall CC of bird echo is low, mainly distributed in the range of 0.1-0.8. And then from the differential reflectivity （ZDR） products, we can see that the distribution of ZDR is not uniform, up to 3-5 dB as the highest. Compared to single polarization weather radar, S-band dual-polarization weather radar has significant advantages in recognizing biological echoes in the sky.
2024, 50(9):1153-1160.
DOI: 10.7519/j.issn.1000-0526.2024.080901
Abstract:
The main characteristics of the general circulation of atmosphere in June 2024 are as follows. There were four polar vortex centers in the Northern Hemisphere. The circulation of the mid-high latitude westerlies was distributed in the pattern of four upper-level troughs and four ridges of high pressure, and the position of frontal zone was generally by north. The western Pacific subtropical high was obviously stronger, located more westward than normal during this month. The monthly mean temperature of China was 0.6℃ higher than the normal June temperature (20.4℃). During this month, four high temperature processes were experienced in Northwest China, North China and the Yellow River and Huaihe River regions. With the outbreak of the Indian monsoon and the middle and lower reaches of the Yangtze River into the Meiyu season on 17 June, the monthly average precipitation of China was more than the usual precipitation 102.8 mm by 11.9%. Totally, five regional torrential rain events occurred in most parts of southern China, especially in the south regions of the Yangtze River and Huaihe River where the accumulated precipitation was more excessive clearly. In addition, precipitation in some regions broke the record of extreme precipitation for the same period.
The main characteristics of the general circulation of atmosphere in June 2024 are as follows. There were four polar vortex centers in the Northern Hemisphere. The circulation of the mid-high latitude westerlies was distributed in the pattern of four upper-level troughs and four ridges of high pressure, and the position of frontal zone was generally by north. The western Pacific subtropical high was obviously stronger, located more westward than normal during this month. The monthly mean temperature of China was 0.6℃ higher than the normal June temperature (20.4℃). During this month, four high temperature processes were experienced in Northwest China, North China and the Yellow River and Huaihe River regions. With the outbreak of the Indian monsoon and the middle and lower reaches of the Yangtze River into the Meiyu season on 17 June, the monthly average precipitation of China was more than the usual precipitation 102.8 mm by 11.9%. Totally, five regional torrential rain events occurred in most parts of southern China, especially in the south regions of the Yangtze River and Huaihe River where the accumulated precipitation was more excessive clearly. In addition, precipitation in some regions broke the record of extreme precipitation for the same period.
Mobile website
® 2025 All Rights Reserved
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
ISSN:1000-0526 CN:11-2282/P