ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,2024 Issue 8
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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(8):905-916, DOI: 10.7519/j.issn.1000-0526.2024.040101
Abstract:
The snowfall in Beijing on 12 January 2023 was the snowfall first 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, with the focus on causes of complex phase distribution and variation. The findings indicate that the low-level warm and wet southerly jet stream provided abundant moisture for the precipitation. However, a lack of uplifting of warm and wet air by cold east winds and weak upper trough resulted in relatively low precipitation amount. Meanwhile, the northeast wind just above the surface did not play the role of cold cushion, so not conducive to the maintenance of snow and the snowfall in the whole city. The disparity at the height of the 0℃-layer between western and eastern parts of 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 processes is the main reason for the rapid decrease of 0℃-layer height to below 500 m, which caused rain to snow in plain areas. The thickened warm layer >0℃ and the decreased snowflake size and density above the melting layer caused snow to turn into rain when reaching the ground. When it comes to forecasting precipitation types, deterministic models failed to accurately depict the snow-melting process, but the short-range ensemble forecast results can compensate for the errors in deterministic models. Integrating the data of cloud radar, micro rain radar and microwave radiometer can enhance our ability to monitor and analyze snow formation within clouds and melting in the boundary layer, and improve the accuracy of now casting of precipitation types.
The snowfall in Beijing on 12 January 2023 was the snowfall first 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, with the focus on causes of complex phase distribution and variation. The findings indicate that the low-level warm and wet southerly jet stream provided abundant moisture for the precipitation. However, a lack of uplifting of warm and wet air by cold east winds and weak upper trough resulted in relatively low precipitation amount. Meanwhile, the northeast wind just above the surface did not play the role of cold cushion, so not conducive to the maintenance of snow and the snowfall in the whole city. The disparity at the height of the 0℃-layer between western and eastern parts of 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 processes is the main reason for the rapid decrease of 0℃-layer height to below 500 m, which caused rain to snow in plain areas. The thickened warm layer >0℃ and the decreased snowflake size and density above the melting layer caused snow to turn into rain when reaching the ground. When it comes to forecasting precipitation types, deterministic models failed to accurately depict the snow-melting process, but the short-range ensemble forecast results can compensate for the errors in deterministic models. Integrating the data of cloud radar, micro rain radar and microwave radiometer can enhance our ability to monitor and analyze snow formation within clouds and melting in the boundary layer, and improve the accuracy of now casting of precipitation types.
QIN Hao, FAN Jiao, NONG Mengsong, LAI Zhenquan, ZHAI Shunan, LIU Le, LIU Xiaomei, PANG Fang, ZHOU Yijing, QIU Zi
2024,50(8):917-928, DOI: 10.7519/j.issn.1000-0526.2024.030801
Abstract:
Guangxi encountered a process of double-convective-bands from 20:00 BT 25 to 08:00 BT 26 March 2023. This process was significantly different from that of the double rain belts in the past, causing significant deviations in the subjective and objective forecasts. Based on multi-source observation data and ERA5 reanalysis data, the Rossby wave energy dispersion, moist potential vorticity and horizontal frontogenic forcing in this process are analyzed. The results show that this process occurred under the background of large-scale circulation adjustment. The two Rossby wave trains that originated from the polar vortex and the Black Sea in the mid- and high-latitude jointly promoted the gradual vertical rotation of the transversal trough in the northeast region, guiding the mid- and high-latitude cold air further southward. During this period, the south branch trough in the low latitude gradually moved eastward, providing the dynamic lifting above the cold cushion in Guangxi, and also promoting the convergence of cold and warm airs in the low troposphere in Guangxi. With the addition of cold air to south and the southerly winds advancing northward under the inertial oscillation, the convergence of warm and cold airs in Guangxi was enhanced. The enhancement of atmospheric moist baroclinicity led to the development of moist potential vorticity, resulting in conditional symmetric instability of stratification. The warm-moist air climbed from south to north reaching 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 north-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, leading to 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 and development of the south-branch convective system when it passed through, and formed bow echo due to the mid-level dry air entrainment. In order to capture the key information of the occurrence and development of elevated convection after the north-branch front, it is necessary to focus on the numerical model in forecasting the mid-level trough and the thermo dynamic conditions above the cold air cushion.
Guangxi encountered a process of double-convective-bands from 20:00 BT 25 to 08:00 BT 26 March 2023. This process was significantly different from that of the double rain belts in the past, causing significant deviations in the subjective and objective forecasts. Based on multi-source observation data and ERA5 reanalysis data, the Rossby wave energy dispersion, moist potential vorticity and horizontal frontogenic forcing in this process are analyzed. The results show that this process occurred under the background of large-scale circulation adjustment. The two Rossby wave trains that originated from the polar vortex and the Black Sea in the mid- and high-latitude jointly promoted the gradual vertical rotation of the transversal trough in the northeast region, guiding the mid- and high-latitude cold air further southward. During this period, the south branch trough in the low latitude gradually moved eastward, providing the dynamic lifting above the cold cushion in Guangxi, and also promoting the convergence of cold and warm airs in the low troposphere in Guangxi. With the addition of cold air to south and the southerly winds advancing northward under the inertial oscillation, the convergence of warm and cold airs in Guangxi was enhanced. The enhancement of atmospheric moist baroclinicity led to the development of moist potential vorticity, resulting in conditional symmetric instability of stratification. The warm-moist air climbed from south to north reaching 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 north-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, leading to 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 and development of the south-branch convective system when it passed through, and formed bow echo due to the mid-level dry air entrainment. In order to capture the key information of the occurrence and development of elevated convection after the north-branch front, it is necessary to focus on the numerical model in forecasting the mid-level trough and the thermo dynamic conditions above the cold air cushion.
2024,50(8):929-940, DOI: 10.7519/j.issn.1000-0526.2023.071002
Abstract:
The severe convective rainstorm that occurred on the west side of Liupan Mountains on 15 July 2022, which is missed by both the numerical weather prediction models and the subjective forecast of forecasters, is analyzed based on the data from regional weather stations, X-band dual-polarization weather radar, C-band Doppler weather radar, wind profiler radar, and the ERA5 hourly reanalysis and conventional observation data. The results show that the rainstorm occurred in the northwest side of the western Pacific subtropical high. The main area of severe rainfall was the south side of the low-level shear line and the left-front side of the low-level jet. Affected by the terrain of Liupan Mountains, the mesoscale ground convergence line, mesoscale low-level southwest jet and mesoscale vortex might be important systems of triggering, maintaining and enhancing of the process. The rainstorm was caused by two mesoscale echo bands, on which the convective cells propagated backward, forming obvious train effect. The strengthening low-level jet, the increasing vertical wind shear, the downward disturbance of wind speed in the jet, and the dry intrusion appeared 1-2 h ahead of the increase in 5 min precipitation, which has a certain reference value for rainstorm forecast and early warning. The center of severe rainfall has a better corresponding relationship with the echo area with intensity ≥50 dBz and the large value area of vertical integrated liquid water, the echo tops, the large ranges of differential phase shift (KDP) and differential reflectivity (ZDR). KDP is a good indicator for intensity of severe rainfall. The maximum values of KDP and ZDR appeared 10 min earlier than the maximum rainfall in five minutes. The ZDR arc and ZDR column also appear 10-20 min earlier than the maximum rainfall. During the heaviest 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, which suggests that the spectrum of rain particulates contained a large amount of relatively large-sized raindrops, increasing the extremity of precipitation.
The severe convective rainstorm that occurred on the west side of Liupan Mountains on 15 July 2022, which is missed by both the numerical weather prediction models and the subjective forecast of forecasters, is analyzed based on the data from regional weather stations, X-band dual-polarization weather radar, C-band Doppler weather radar, wind profiler radar, and the ERA5 hourly reanalysis and conventional observation data. The results show that the rainstorm occurred in the northwest side of the western Pacific subtropical high. The main area of severe rainfall was the south side of the low-level shear line and the left-front side of the low-level jet. Affected by the terrain of Liupan Mountains, the mesoscale ground convergence line, mesoscale low-level southwest jet and mesoscale vortex might be important systems of triggering, maintaining and enhancing of the process. The rainstorm was caused by two mesoscale echo bands, on which the convective cells propagated backward, forming obvious train effect. The strengthening low-level jet, the increasing vertical wind shear, the downward disturbance of wind speed in the jet, and the dry intrusion appeared 1-2 h ahead of the increase in 5 min precipitation, which has a certain reference value for rainstorm forecast and early warning. The center of severe rainfall has a better corresponding relationship with the echo area with intensity ≥50 dBz and the large value area of vertical integrated liquid water, the echo tops, the large ranges of differential phase shift (KDP) and differential reflectivity (ZDR). KDP is a good indicator for intensity of severe rainfall. The maximum values of KDP and ZDR appeared 10 min earlier than the maximum rainfall in five minutes. The ZDR arc and ZDR column also appear 10-20 min earlier than the maximum rainfall. During the heaviest 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, which suggests that the spectrum of rain particulates contained a large amount of relatively large-sized raindrops, increasing the extremity of precipitation.
ZHOU Yan, ZHAI Liping, ZHANG Dingding, FAN Sheng, HUANG Zhuofan, LI Yuping, LI Zitian, PAN Jieli, HUANG Zengjun
2024,50(8):941-952, DOI: 10.7519/j.issn.1000-0526.2024.071001
Abstract:
On June 13, 2022, a large-scale regional 〖JP2〗rainstorm event occurred in Guangxi. During this period,〖JP〗 a rainstorm false alarm was issued for the downtown area of Nanning. The echo attenuated in the north side of Nanning City, maintained in the east side and developed in the south side, which made the process complicated. This article investigates the causes for the generation and dissipation of the convection during this event by utilizing various observational data and ERA5 reanalysis data. The results are as follows. The circulation background of this process was the typical heavy rainfall circulation and ambient condition in the first rainy season in Guangxi. However, under the combined influence of synoptic-scale cold advection and storm cold pool, the cold air quickly moved over Nanning City, and the outflow boundary formed by the storm in the north side of Nanning moved away from the storm parent body. Meanwhile, the low-level water vapor transport in the front of the storm moved eastward, resulting in poor thermodynamic and dynamic conditions, leading to the attenuation and dissipation of echoes in the north side of Nanning City. In the east side of Nanning City, the outflow boundary of the storm was next to the storm parent body during its advancing, and the lower layer ahead of the storm kept the southwest jet stream so that the storm was strengthened or sustained by continuous convective cells triggered along the outflow boundary. There was a low-level high temperature and high humidity environment in the south side of Nanning, which was conducive to the reconstruction or enhancement of convective available potential energy. Based on the above, a conceptual model of the evolution mechanism of convection generation and dissipation in this process has been built, and with it, the short-time and nowcasting forecasts can be supplemented and corrected by analyzing the evolution of cold pool, outflow boundary and ambient conditions.
On June 13, 2022, a large-scale regional 〖JP2〗rainstorm event occurred in Guangxi. During this period,〖JP〗 a rainstorm false alarm was issued for the downtown area of Nanning. The echo attenuated in the north side of Nanning City, maintained in the east side and developed in the south side, which made the process complicated. This article investigates the causes for the generation and dissipation of the convection during this event by utilizing various observational data and ERA5 reanalysis data. The results are as follows. The circulation background of this process was the typical heavy rainfall circulation and ambient condition in the first rainy season in Guangxi. However, under the combined influence of synoptic-scale cold advection and storm cold pool, the cold air quickly moved over Nanning City, and the outflow boundary formed by the storm in the north side of Nanning moved away from the storm parent body. Meanwhile, the low-level water vapor transport in the front of the storm moved eastward, resulting in poor thermodynamic and dynamic conditions, leading to the attenuation and dissipation of echoes in the north side of Nanning City. In the east side of Nanning City, the outflow boundary of the storm was next to the storm parent body during its advancing, and the lower layer ahead of the storm kept the southwest jet stream so that the storm was strengthened or sustained by continuous convective cells triggered along the outflow boundary. There was a low-level high temperature and high humidity environment in the south side of Nanning, which was conducive to the reconstruction or enhancement of convective available potential energy. Based on the above, a conceptual model of the evolution mechanism of convection generation and dissipation in this process has been built, and with it, the short-time and nowcasting forecasts can be supplemented and corrected by analyzing the evolution of cold pool, outflow boundary and ambient conditions.
2024,50(8):953-965, DOI: 10.7519/j.issn.1000-0526.2024.071401
Abstract:
Forecasting the warm-sector rainstorm of low vortex shear type is a difficult point in the rainstorm forecasting operation of Shandong Province. From 30 to 31 August 2021, a large range of warm-sector rainstorm occurred in the central and peninsula area of Shandong Province, but the forecasted rainfall intensity was weaker and affected area was smaller than the observed, resulting in the missing report of the rainstorm in a large scale. Based on numerical forecast products, conventional surface and upper-air observation data, Doppler radar data, we review the forecast errors of this warm-sector rainstorm event. The findings suggest that, during the forecasting process, the symmetric instability characteristics of atmosphere, the characteristics of warm front frontogenesis in the boundary layer, the vertical interactions of ultra-low level jet, low-level jet and upper-level jet, and the function of weak cold air in the boundary layer and middle layer failed to be judged completely by forecasters. In the case that the environmental field had changed, the model products in a short time in the previous period were still used as the basis for the precipitation correction of the model results. This may be the critical reason for the insufficient forecast of this warm-sector rainstorm process. In the future, when forecasting the similar warm-sector rainstorms, forecasters should comprehensively analyze the characteristics of conditional instability, convective instability and symmetric instability, and also pay attention to the characteristics of boundary layer θse dense zone and the warm front frontogenesis characteristics of the boundary layer. Moreover, the vertical three-dimensional structure of jet stream and the role of weak cold air at different heights should be considered, and the overestimation or underestimation of rainstorm forecast by the numerical models should be judged according to the environmental field features, and then reasonable dynamic model correction should be carried out.
Forecasting the warm-sector rainstorm of low vortex shear type is a difficult point in the rainstorm forecasting operation of Shandong Province. From 30 to 31 August 2021, a large range of warm-sector rainstorm occurred in the central and peninsula area of Shandong Province, but the forecasted rainfall intensity was weaker and affected area was smaller than the observed, resulting in the missing report of the rainstorm in a large scale. Based on numerical forecast products, conventional surface and upper-air observation data, Doppler radar data, we review the forecast errors of this warm-sector rainstorm event. The findings suggest that, during the forecasting process, the symmetric instability characteristics of atmosphere, the characteristics of warm front frontogenesis in the boundary layer, the vertical interactions of ultra-low level jet, low-level jet and upper-level jet, and the function of weak cold air in the boundary layer and middle layer failed to be judged completely by forecasters. In the case that the environmental field had changed, the model products in a short time in the previous period were still used as the basis for the precipitation correction of the model results. This may be the critical reason for the insufficient forecast of this warm-sector rainstorm process. In the future, when forecasting the similar warm-sector rainstorms, forecasters should comprehensively analyze the characteristics of conditional instability, convective instability and symmetric instability, and also pay attention to the characteristics of boundary layer θse dense zone and the warm front frontogenesis characteristics of the boundary layer. Moreover, the vertical three-dimensional structure of jet stream and the role of weak cold air at different heights should be considered, and the overestimation or underestimation of rainstorm forecast by the numerical models should be judged according to the environmental field features, and then reasonable dynamic model correction should be carried out.
2024,50(8):966-980, 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 east of Hebei Province on 19 June 2017. In this paper, the evolution characteristics and maintenance mechanism of this supercell storm are mainly analyzed. The results indicate that the sea breeze front and the gust front of the multi-cell strong storm, the tongue-shaped high temperature and high humidity area in the lower layer provided better thermal and dynamic conditions for the formation of the supercell. When the convection cell moved into the tongue area, it rapidly developed into a supercell and moved southeastward along the outflow boundary of multi-cell strong storm. The relatively stable gust front fed by the slowly weakening severe thunderstorm not only provided long-time dynamic conditions for the development and maintenance of supercell, but also guided its movement. This is of great significance for the short-time and nowcasting of 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 turned to stronger easterly winds, changing the configuration of mesoscale environment significantly. The vertical wind shear of 0-6 km increased to 27 m·s-1 and the shear of 0-3 km increased to 17-19 m·s-1, which was the main reason for the rapid formation of mesocyclone. The strong vertical vorticity advection on the convergence line was 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 was always about 20 m·s-1, the baroclinic vortex effect was obvious, providing a large and long-time horizontal vorticity input for the development and maintenance of supercell. During the formation and development of supercell, the storm relative helicity (SRH) was between 140 m2·s-2 and 171 m2·s-2, and exceeded 150 m2·s-2 for most of the time. Before the formation of supercell and near the dissipation stage, the SRH was significantly less than 150 m2·s-2. This indicates the SRH has a clear indication for the occurrence and development of supercell. The outflow of the cold pool preceded the formation of the supercell, strengthening the convergence and uplift of the inflow. This was conducive to the development and maintenance of the supercell. In addition, there were more cells splitting from parent storm, which to some extent weakened the strong development of the supercell, but it just made the sinking outflow not too strong but made the gust front move away quickly, causing the cold pool always to keep a certain intensity. At the same time, the front of multi-cell storm provided a stable vertical wind shear of 0-3 km (maintained at about 20 m·s-1) for the supercell. This resulted in a long-time balance between the wind shear and the strength of the cold pool, and finally made supercell maintain a stable state for a long time. In a word, the main reason why the supercell maintained self-organization for a long time is that the appropriate vertical wind shear provided by the mesoscale envir-onment kept 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 east of Hebei Province on 19 June 2017. In this paper, the evolution characteristics and maintenance mechanism of this supercell storm are mainly analyzed. The results indicate that the sea breeze front and the gust front of the multi-cell strong storm, the tongue-shaped high temperature and high humidity area in the lower layer provided better thermal and dynamic conditions for the formation of the supercell. When the convection cell moved into the tongue area, it rapidly developed into a supercell and moved southeastward along the outflow boundary of multi-cell strong storm. The relatively stable gust front fed by the slowly weakening severe thunderstorm not only provided long-time dynamic conditions for the development and maintenance of supercell, but also guided its movement. This is of great significance for the short-time and nowcasting of 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 turned to stronger easterly winds, changing the configuration of mesoscale environment significantly. The vertical wind shear of 0-6 km increased to 27 m·s-1 and the shear of 0-3 km increased to 17-19 m·s-1, which was the main reason for the rapid formation of mesocyclone. The strong vertical vorticity advection on the convergence line was 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 was always about 20 m·s-1, the baroclinic vortex effect was obvious, providing a large and long-time horizontal vorticity input for the development and maintenance of supercell. During the formation and development of supercell, the storm relative helicity (SRH) was between 140 m2·s-2 and 171 m2·s-2, and exceeded 150 m2·s-2 for most of the time. Before the formation of supercell and near the dissipation stage, the SRH was significantly less than 150 m2·s-2. This indicates the SRH has a clear indication for the occurrence and development of supercell. The outflow of the cold pool preceded the formation of the supercell, strengthening the convergence and uplift of the inflow. This was conducive to the development and maintenance of the supercell. In addition, there were more cells splitting from parent storm, which to some extent weakened the strong development of the supercell, but it just made the sinking outflow not too strong but made the gust front move away quickly, causing the cold pool always to keep a certain intensity. At the same time, the front of multi-cell storm provided a stable vertical wind shear of 0-3 km (maintained at about 20 m·s-1) for the supercell. This resulted in a long-time balance between the wind shear and the strength of the cold pool, and finally made supercell maintain a stable state for a long time. In a word, the main reason why the supercell maintained self-organization for a long time is that the appropriate vertical wind shear provided by the mesoscale envir-onment kept balance with the development of the storm.
2024,50(8):981-996, DOI: 10.7519/j.issn.1000-0526.2023.121101
Abstract:
To reveal the weather causes of the rainstorm process that caused the heavy flood in the Mintuo River and Jialing River basins, the rainfall and flood law at Yichang Control Station, and to deepen the research on the occurrence and development mechanism of heavy flood at Yichang Station, based on the NCEP/NCAR reanalysis data and the conventional meteorological and hydrological observation data, this paper analyzes the characteristics of 19 flood-causing rainstorm processes that occurred in the Mintuo River and Jialing River basins from 1980 to 2020 by means of statistical and synoptic methods. At the sametime, the relationship between rainstorm and flood, flood-causing rainstorm source, underlying surface characteristics, and weather system configuration, etc. are also analyzed. The results show that as the main control station in the Yangtze River Basin, Yichang Station has an initial inflow of more than 19 000 m3·s-1 in the current period, and it just encounters a continuous rainstorm process, so the probability of major floods is greatly increased. The duration from the beginning of the continuous rainstorm process in Mintuo River or Jialing River to the flood peak is about 6 days on average. The rainstorm duration and accumulated area rainfall have a good corresponding relationship with the flood peak. The formation of each major flood requires a rainstorm process lasting more than 3 days, mostly 4-6 days. All of the flood processes occur from July to September. The process of flood-causing rainstorm is dominated by quasi-static rain belt, followed by easterly type and turning type. 89% of the process rain bands are distributed in a northeast-southwest direction. The central source of severe precipitation is closely related to special terrain, mainly distributed in three places: first, the intersection of the lower reaches of the Minjiang River and the Qingyi River, where turning precipitation mostly occurs; second, the middle and lower reaches of the Jia-ling River, the Fujiang River Basin, and the Qujiang River Basin are mostly of quasi-static type; third, 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. The existence of the Bay of Bengal tropical depression system is critical to the continuous rainstorm in the upstream, followed by the low value system in the South China Sea, which accounts for 68% of the process. The depression system not only brings 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 vortexes in the Mintuo River and Jialing River basins, combined with special terrain, resulting in strong upward motion. The precipitation process is divided into two categories: quasi-static persistent precipitation and mobile persistent precipitation. There are three types of synoptic conceptual models that are prone to major floods. Type Ⅰ is rainstorm type triggered by westerly short-wave eastward movement at the edge of Western Pacific subtropical high. Type Ⅱ is the rainstorm type triggered by the eastward movement of the low value system of the Tibetan Plateau. Type Ⅲ is a low-level easterly air flow rainstorm type.
To reveal the weather causes of the rainstorm process that caused the heavy flood in the Mintuo River and Jialing River basins, the rainfall and flood law at Yichang Control Station, and to deepen the research on the occurrence and development mechanism of heavy flood at Yichang Station, based on the NCEP/NCAR reanalysis data and the conventional meteorological and hydrological observation data, this paper analyzes the characteristics of 19 flood-causing rainstorm processes that occurred in the Mintuo River and Jialing River basins from 1980 to 2020 by means of statistical and synoptic methods. At the sametime, the relationship between rainstorm and flood, flood-causing rainstorm source, underlying surface characteristics, and weather system configuration, etc. are also analyzed. The results show that as the main control station in the Yangtze River Basin, Yichang Station has an initial inflow of more than 19 000 m3·s-1 in the current period, and it just encounters a continuous rainstorm process, so the probability of major floods is greatly increased. The duration from the beginning of the continuous rainstorm process in Mintuo River or Jialing River to the flood peak is about 6 days on average. The rainstorm duration and accumulated area rainfall have a good corresponding relationship with the flood peak. The formation of each major flood requires a rainstorm process lasting more than 3 days, mostly 4-6 days. All of the flood processes occur from July to September. The process of flood-causing rainstorm is dominated by quasi-static rain belt, followed by easterly type and turning type. 89% of the process rain bands are distributed in a northeast-southwest direction. The central source of severe precipitation is closely related to special terrain, mainly distributed in three places: first, the intersection of the lower reaches of the Minjiang River and the Qingyi River, where turning precipitation mostly occurs; second, the middle and lower reaches of the Jia-ling River, the Fujiang River Basin, and the Qujiang River Basin are mostly of quasi-static type; third, 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. The existence of the Bay of Bengal tropical depression system is critical to the continuous rainstorm in the upstream, followed by the low value system in the South China Sea, which accounts for 68% of the process. The depression system not only brings 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 vortexes in the Mintuo River and Jialing River basins, combined with special terrain, resulting in strong upward motion. The precipitation process is divided into two categories: quasi-static persistent precipitation and mobile persistent precipitation. There are three types of synoptic conceptual models that are prone to major floods. Type Ⅰ is rainstorm type triggered by westerly short-wave eastward movement at the edge of Western Pacific subtropical high. Type Ⅱ is the rainstorm type triggered by the eastward movement of the low value system of the Tibetan Plateau. Type Ⅲ is a low-level easterly air flow rainstorm type.
2024,50(8):997-1011, 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 train effect of typhoon rainbands, we comparatively analyze the circulation situation and the convection organization of three heavy rainfall processes related to train effect 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 multi-source observation data and the ERA5 reanalysis data. The results show that the extreme precipitation of the three processes all occurred on the windward slope of the hills in the eastern part of Zhejiang Province. The directions of the rainbands were consistent with the background air flows, and convergence of water vapor flux was mainly concentrated below 850 hPa. However, the ambient backgrounds of the three processes are different obviously. In process 1, the rainband happend between the low pressure and the subtropical high, the vertical wind shear and the CAPE were large, the water vapor came from tropical ocean surface, and the wet layer was thick. Process 2 took place in a saddle-shaped field between the residual vortex of a typhoon over land and another typhoon over the sea. The vertical wind shear and CAPE were weak, water vapor was from the sea surface at the same latitude, and the wet layer was located in the middle and lower level of the troposphere. Process 3 was caused by the spiral rainband in the core zone of typhoon. The vertical wind shear was strong and the CAPE was the minimum. Moreover, the structure and organization of the rainbands in the three process are obviously different. In process 1, the boundary layer convergence and the convective system highly developed, the baroclinic structure of the mesoscale convergence line promoted 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 was opposited to the easterly airflow, while with similar wind speed and shallow convergence. The warm cloud rain was dominant. The new cells continued to form at the eastern boundary of the rainbands, and dissipated at the western boundary. The stagnation of rainband caused continuous belt-like heavy rainfall area. In process 3, the spiral bands in the inner-core section of typhoon were affected by the typhoon vortex dynamics, the convection developed at lower height, and the structure tilted slightly to the outside. The rainband developed with the wind speed convergence caused by the fluctuating of southeast jet, which resulted in extreme rainfall. The above facts show that the train effect of typhoon rainbands causing extreme precipitation can be formed in various ways, so there are great challenges faced in the short-time forecasting and nowcasting of such extreme precipitation.
In order to explore the possible formation mechanism and flow pattern of extreme precipitation caused by the train effect of typhoon rainbands, we comparatively analyze the circulation situation and the convection organization of three heavy rainfall processes related to train effect 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 multi-source observation data and the ERA5 reanalysis data. The results show that the extreme precipitation of the three processes all occurred on the windward slope of the hills in the eastern part of Zhejiang Province. The directions of the rainbands were consistent with the background air flows, and convergence of water vapor flux was mainly concentrated below 850 hPa. However, the ambient backgrounds of the three processes are different obviously. In process 1, the rainband happend between the low pressure and the subtropical high, the vertical wind shear and the CAPE were large, the water vapor came from tropical ocean surface, and the wet layer was thick. Process 2 took place in a saddle-shaped field between the residual vortex of a typhoon over land and another typhoon over the sea. The vertical wind shear and CAPE were weak, water vapor was from the sea surface at the same latitude, and the wet layer was located in the middle and lower level of the troposphere. Process 3 was caused by the spiral rainband in the core zone of typhoon. The vertical wind shear was strong and the CAPE was the minimum. Moreover, the structure and organization of the rainbands in the three process are obviously different. In process 1, the boundary layer convergence and the convective system highly developed, the baroclinic structure of the mesoscale convergence line promoted 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 was opposited to the easterly airflow, while with similar wind speed and shallow convergence. The warm cloud rain was dominant. The new cells continued to form at the eastern boundary of the rainbands, and dissipated at the western boundary. The stagnation of rainband caused continuous belt-like heavy rainfall area. In process 3, the spiral bands in the inner-core section of typhoon were affected by the typhoon vortex dynamics, the convection developed at lower height, and the structure tilted slightly to the outside. The rainband developed with the wind speed convergence caused by the fluctuating of southeast jet, which resulted in extreme rainfall. The above facts show that the train effect of typhoon rainbands causing extreme precipitation can be formed in various ways, so there are great challenges faced in the short-time forecasting and nowcasting of such extreme precipitation.
2024,50(8):1012-1023, DOI: 10.7519/j.issn.1000-0526.2024.061301
Abstract:
Using the observation data of micro rain radar, raindrop disdrometer and 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 in a mixed cloud precipitation process at Changbai Mountain are analyzed. The results show that the rainfall variation trend with high resolution of 150 m retrieved by micro rain radar and the ground rainfall measured by raindrop disdrometer and rain gauge are basically consistent, but there are some deviations between the observed values and inversion values. The Gamma function goodness of fit clocks up 0.99 for the 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) retrieved by micro rain radar is significantly smaller. Research also shows that raindrops in different diameters have different contributions to microphysical parameters at different heights. For small raindrops (D≤1.0 mm), its contribution rate to rainfall intensity, reflectivity factor, liquid water content, and total number concentration decreases generally with lowering height. However, the contribution rate of medium raindrops （1.0 mm＜D≤3.0 mm） and large raindrops to these parameters increases as height declines. Besides, the evaporation and coagulation effects of raindrops show varieties in different precipitation stages. In the early precipitation stage, the evaporation effects of raindrops is stronger due to higher temperature and lower relative humidity in the falling process of raindrops. In the stage of concentrated precipitation, the coagulation effect of raindrops is more evident with the relative humidity approaching saturation.
Using the observation data of micro rain radar, raindrop disdrometer and 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 in a mixed cloud precipitation process at Changbai Mountain are analyzed. The results show that the rainfall variation trend with high resolution of 150 m retrieved by micro rain radar and the ground rainfall measured by raindrop disdrometer and rain gauge are basically consistent, but there are some deviations between the observed values and inversion values. The Gamma function goodness of fit clocks up 0.99 for the 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) retrieved by micro rain radar is significantly smaller. Research also shows that raindrops in different diameters have different contributions to microphysical parameters at different heights. For small raindrops (D≤1.0 mm), its contribution rate to rainfall intensity, reflectivity factor, liquid water content, and total number concentration decreases generally with lowering height. However, the contribution rate of medium raindrops （1.0 mm＜D≤3.0 mm） and large raindrops to these parameters increases as height declines. Besides, the evaporation and coagulation effects of raindrops show varieties in different precipitation stages. In the early precipitation stage, the evaporation effects of raindrops is stronger due to higher temperature and lower relative humidity in the falling process of raindrops. In the stage of concentrated precipitation, the coagulation effect of raindrops is more evident with the relative humidity approaching saturation.
2024,50(8):1024-1032, DOI: 10.7519/j.issn.1000-0526.2024.070801
Abstract:
The main characteristics of the general circulation in May 2024 are that the polar vortex in the Northern Hemisphere was partially mono-polar with stronger intensity than usual. The 500 hPa geopotential height presented the distribution of a four-wave pattern in middle-high latitudes of the Northern Hemisphere, which means that the circulation had transformed from a three-wave pattern in winter into a four-wave pattern in summer, and the meridional degree of the Eurasian circulation was relatively high. The western Pacific subtropical high was stronger and located more westerly and northerly than that in normal years, while the south branch trough was weaker than usual. The monthly mean temperature across China in May was 17.7℃, 1.2℃ warmer than normal. The monthly mean precipitation was 69.5 mm, which is 1% less than normal. During this month, five regional torrential rain processes occurred in China, but the South China Sea summer monsoon erupted in the sixth pentad (May 26), 2 pentads later than the normal onset time in the fourth pentad in May. In addition, three severe convection weather events occurred this month, making the hit areas suffer from gales and hailstorm. Moreover, the northern part of China was troubled by two sand-dust events in this month.
The main characteristics of the general circulation in May 2024 are that the polar vortex in the Northern Hemisphere was partially mono-polar with stronger intensity than usual. The 500 hPa geopotential height presented the distribution of a four-wave pattern in middle-high latitudes of the Northern Hemisphere, which means that the circulation had transformed from a three-wave pattern in winter into a four-wave pattern in summer, and the meridional degree of the Eurasian circulation was relatively high. The western Pacific subtropical high was stronger and located more westerly and northerly than that in normal years, while the south branch trough was weaker than usual. The monthly mean temperature across China in May was 17.7℃, 1.2℃ warmer than normal. The monthly mean precipitation was 69.5 mm, which is 1% less than normal. During this month, five regional torrential rain processes occurred in China, but the South China Sea summer monsoon erupted in the sixth pentad (May 26), 2 pentads later than the normal onset time in the fourth pentad in May. In addition, three severe convection weather events occurred this month, making the hit areas suffer from gales and hailstorm. Moreover, the northern part of China was troubled by two sand-dust events in this month.
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Available online: August 28, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.081501
Abstract:
Based on the measured hourly precipitations at 38 meteorological stations in Tibet from 1981 to 2020, the spatio-temporal characteristics of daytime/nighttime precipitation(Pd/Pn) and night-rain rate(Nr) in recent 40 years were analyzed by the methods of linear trend estimation, Person coefficient, Mann-Kendall and dominance analysis. The results show that:(1) As a whole in Tibet, the multi-year average of annual Pd decreased from east to west, the annual Pn decreased from southeast to northwest, and Pn was larger than Pd. The middle reaches of the Yarlung Zangbo River were the center of night rain in Tibet with the Nr greater than 70.0%, which decreased toward the periphery from the center. The Pd/Pn was mainly affected by the site altitude in spring, but the Pd/Pn was affected by the site longitude in summer, in autumn and for the whole year. In winter, Nr at high latitudes was larger than that at low latitudes. In summer and autumn, Nr at high altitudes was smaller than that at low altitudes. (2) In the past 40 years, the annual Pd/Pn increased at 73.7% of stations in Tibet. However, the annual Nr showed a decreasing trend at 57.9% of stations. Wherein, the trend of Pn was more obvious than that of Pd at 63.2% of stations. The Pd/Pn co-increasing type accounted for 63.2%, the Pd/Pn co-decreasing type accounted for 15.8%, and the case of Pd increasing Pn decreasing accounted for 10.5%, which was equal to the ratio of the Pd decreasing Pn increasing type. (3) In the past 40 years, the average annual Pd increased at a rate of 4.40mm/10a in Tibet, mainly in spring and summer. The annual Pn also increased with a rate of 6.32mm/10a, which was greater than the growth rate of Pd. Due to the decreased of Nr in winter, spring and autumn, the annual Nr tended to decrease(-0.64%/10a). (4) On the decadal scale, the Pd and Pn in the 1980s was significantly small in Tibet, which was the least in the past 40 years. The maxima of anunal Pd and Pn appeared in 2010s and in 1990s, respectively. For Nr, the maximum and minimum occurred in the 1980s and in the 2010s, respectively. (5) According to the M-K mutation test, the abrupt changes of climate for the Pd/Pn in spring and Pn in winter occurred in the late 1990s and at the beginning of 21st century, respectively, with the former increasing and the latter decreasing. The mutation time of Nr in winter and spring appeared in 2004 and 2011 respectively, and the mutation point of annual Nr was in 2009. Whereas, the mutation time of annual Nr was in 2009. These results are beneficial to comprehensively understand the impacts of global warming on diurnal cycle of regional precipitation in Tibet.
Based on the measured hourly precipitations at 38 meteorological stations in Tibet from 1981 to 2020, the spatio-temporal characteristics of daytime/nighttime precipitation(Pd/Pn) and night-rain rate(Nr) in recent 40 years were analyzed by the methods of linear trend estimation, Person coefficient, Mann-Kendall and dominance analysis. The results show that:(1) As a whole in Tibet, the multi-year average of annual Pd decreased from east to west, the annual Pn decreased from southeast to northwest, and Pn was larger than Pd. The middle reaches of the Yarlung Zangbo River were the center of night rain in Tibet with the Nr greater than 70.0%, which decreased toward the periphery from the center. The Pd/Pn was mainly affected by the site altitude in spring, but the Pd/Pn was affected by the site longitude in summer, in autumn and for the whole year. In winter, Nr at high latitudes was larger than that at low latitudes. In summer and autumn, Nr at high altitudes was smaller than that at low altitudes. (2) In the past 40 years, the annual Pd/Pn increased at 73.7% of stations in Tibet. However, the annual Nr showed a decreasing trend at 57.9% of stations. Wherein, the trend of Pn was more obvious than that of Pd at 63.2% of stations. The Pd/Pn co-increasing type accounted for 63.2%, the Pd/Pn co-decreasing type accounted for 15.8%, and the case of Pd increasing Pn decreasing accounted for 10.5%, which was equal to the ratio of the Pd decreasing Pn increasing type. (3) In the past 40 years, the average annual Pd increased at a rate of 4.40mm/10a in Tibet, mainly in spring and summer. The annual Pn also increased with a rate of 6.32mm/10a, which was greater than the growth rate of Pd. Due to the decreased of Nr in winter, spring and autumn, the annual Nr tended to decrease(-0.64%/10a). (4) On the decadal scale, the Pd and Pn in the 1980s was significantly small in Tibet, which was the least in the past 40 years. The maxima of anunal Pd and Pn appeared in 2010s and in 1990s, respectively. For Nr, the maximum and minimum occurred in the 1980s and in the 2010s, respectively. (5) According to the M-K mutation test, the abrupt changes of climate for the Pd/Pn in spring and Pn in winter occurred in the late 1990s and at the beginning of 21st century, respectively, with the former increasing and the latter decreasing. The mutation time of Nr in winter and spring appeared in 2004 and 2011 respectively, and the mutation point of annual Nr was in 2009. Whereas, the mutation time of annual Nr was in 2009. These results are beneficial to comprehensively understand the impacts of global warming on diurnal cycle of regional precipitation in Tibet.
Available online: August 27, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.081601
Abstract:
In the springtime (March to May, MAM) of 2024, the average precipitation in China was 163 mm, ranking the sixth since 1961. During April–May, eastern region of China experienced both severe droughts and floods. Southern China and most of Jiangnan region experienced significantly above-average rainfall, with parts of southern China exceeding normal levels by over 50%. This led to frequent heavy rain and floods in some areas. Conversely, northern Jianghuai and Huanghuai regions saw notably below-average precipitation, leading to rapid development of drought in later spring. The phenomenon of “Southern China floods, Huanghuai droughts” was mainly influenced by atmospheric circulation anomalies in East Asia and their intraseasonal variation. The abnormally strong and southward-shifted western North Pacific subtropical high (WPSH) and extremely strong anomalous western North Pacific anticyclone (WNPAC) in April provided favorable conditions for moisture transport, leading to intense precipitation events in southern China. The drought over Huanghuai region was primarily dominated by persistent strong high system near the Korean Peninsula-Japan Sea (also known as the Bonin High) in April–May, along with a southward shift of the WPSH. Additionally, the attenuation of El Ni?o and abnormally warm sea surface temperature in the tropical Indian Ocean contributed to the activation of abnormally strong WNPAC, providing important oceanic external forcing background for heavy rainfall in southern China.
In the springtime (March to May, MAM) of 2024, the average precipitation in China was 163 mm, ranking the sixth since 1961. During April–May, eastern region of China experienced both severe droughts and floods. Southern China and most of Jiangnan region experienced significantly above-average rainfall, with parts of southern China exceeding normal levels by over 50%. This led to frequent heavy rain and floods in some areas. Conversely, northern Jianghuai and Huanghuai regions saw notably below-average precipitation, leading to rapid development of drought in later spring. The phenomenon of “Southern China floods, Huanghuai droughts” was mainly influenced by atmospheric circulation anomalies in East Asia and their intraseasonal variation. The abnormally strong and southward-shifted western North Pacific subtropical high (WPSH) and extremely strong anomalous western North Pacific anticyclone (WNPAC) in April provided favorable conditions for moisture transport, leading to intense precipitation events in southern China. The drought over Huanghuai region was primarily dominated by persistent strong high system near the Korean Peninsula-Japan Sea (also known as the Bonin High) in April–May, along with a southward shift of the WPSH. Additionally, the attenuation of El Ni?o and abnormally warm sea surface temperature in the tropical Indian Ocean contributed to the activation of abnormally strong WNPAC, providing important oceanic external forcing background for heavy rainfall in southern China.
Available online: August 23, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061701
Abstract:
In the context of global warming, it is important to accurately estimate the atmospheric CO2 content and its changes. CO2 over the ocean is the vital component of global atmospheric CO2, and it is necessary to monitor it with a high-frequency and full-coverage technology. The atmospheric CO2 content over the South China Sea is affected by continental, oceanic and atmospheric factors. In this paper, a random-forest-based model of atmospheric CO2 column concentration over the South China Sea was built with chlorophyll-a concentration, instantaneous photosynthetically active radiation, particulate inorganic carbon, particulate organic carbon, sea surface temperature, wind speed and wind direction, which were from multisource satellites remote sensing data. The accuracy of the model was verified for the year 2020, with Bias of 0.27ppm, R2 of 0.59 and the RMSE is 1.00 ppm, showing the accuracy is satisfactory. The results show that the atmospheric CO2 column concentration in the South China Sea presents obvious seasonal characteristics, which are spring>summer>winter>autumn. Moreover, the main influencing factors causing the seasonal differences of atmospheric CO2 column concentration in the South China Sea vary with time. In January and April, the main influencing factors are wind direction. In July, wind speed and wind direction are the two most influential factors. In October, sea surface temperature is the most influential factor. This method can realize the high-frequency and full-coverage monitoring of atmospheric CO2 column concentration in the South China Sea. The relevant results can provide help for the realization of carbon neutrality goal.
In the context of global warming, it is important to accurately estimate the atmospheric CO2 content and its changes. CO2 over the ocean is the vital component of global atmospheric CO2, and it is necessary to monitor it with a high-frequency and full-coverage technology. The atmospheric CO2 content over the South China Sea is affected by continental, oceanic and atmospheric factors. In this paper, a random-forest-based model of atmospheric CO2 column concentration over the South China Sea was built with chlorophyll-a concentration, instantaneous photosynthetically active radiation, particulate inorganic carbon, particulate organic carbon, sea surface temperature, wind speed and wind direction, which were from multisource satellites remote sensing data. The accuracy of the model was verified for the year 2020, with Bias of 0.27ppm, R2 of 0.59 and the RMSE is 1.00 ppm, showing the accuracy is satisfactory. The results show that the atmospheric CO2 column concentration in the South China Sea presents obvious seasonal characteristics, which are spring>summer>winter>autumn. Moreover, the main influencing factors causing the seasonal differences of atmospheric CO2 column concentration in the South China Sea vary with time. In January and April, the main influencing factors are wind direction. In July, wind speed and wind direction are the two most influential factors. In October, sea surface temperature is the most influential factor. This method can realize the high-frequency and full-coverage monitoring of atmospheric CO2 column concentration in the South China Sea. The relevant results can provide help for the realization of carbon neutrality goal.
Available online: August 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2027.070101
Abstract:
There was a mixed strong convective process occurred in Huang-Huai Area and Jiang-Huai Area from north to south on 19 September 2023, which accompanied by tornadoes. Funing strong tornado (corresponding to EF3) was the strongest tornado. Tongying village was 1.2 km away from the Funing strong tornado, which observed extremely strong wind of 41.8 m·s-1(level 14). Based on the data from ground automatic stations and sounding stations, data from S-band dual-polarization radar, the Funing strong tornado was analyzed. Results showed that: (1) Tornado occurred in strong warm and moist zone, which between the subtropical anticyclone and the eastern section of the low-level shear line. The slope of low level frontal was large. The convergence line moved southward on the ground rapidly, combined with extremely low LCL and CIN, high CAPE and vertical wind shear, favorable for tornados. (2) The cold pool and high-pressure center appeared behind the thunderstorm would contribute to the development of vertical vorticity near the ground before tornado occurred. But the heavy precipitation adjacent to the front side of the thunderstorm generated cold pool and strong downdrafts, would block the movement and development of the tornado. (3) The Funing strong tornado was a typical heavy rainfall supercell tornado, characterized by hook echo, BWER and deep strong meso-cyclone. The strong echo was slope and extended to 16 km. (4) TDS observed by dual-polarization radar was wide and deep, indicated the tornado process was strong and destructive. Strong ZDR arcs appeared at the head of the hook echo and separated from the strong KDP zone, formed tilt vertical circulation, would promote the development and maintenance of the supercell. Heavy precipitation echo with low centroid appeared in the front of TDS, precipitation and cooling appeared on the ground, and ZDR arcs and ZDR columns weakened and disappeared, and then tornado storm weakened rapidly.
There was a mixed strong convective process occurred in Huang-Huai Area and Jiang-Huai Area from north to south on 19 September 2023, which accompanied by tornadoes. Funing strong tornado (corresponding to EF3) was the strongest tornado. Tongying village was 1.2 km away from the Funing strong tornado, which observed extremely strong wind of 41.8 m·s-1(level 14). Based on the data from ground automatic stations and sounding stations, data from S-band dual-polarization radar, the Funing strong tornado was analyzed. Results showed that: (1) Tornado occurred in strong warm and moist zone, which between the subtropical anticyclone and the eastern section of the low-level shear line. The slope of low level frontal was large. The convergence line moved southward on the ground rapidly, combined with extremely low LCL and CIN, high CAPE and vertical wind shear, favorable for tornados. (2) The cold pool and high-pressure center appeared behind the thunderstorm would contribute to the development of vertical vorticity near the ground before tornado occurred. But the heavy precipitation adjacent to the front side of the thunderstorm generated cold pool and strong downdrafts, would block the movement and development of the tornado. (3) The Funing strong tornado was a typical heavy rainfall supercell tornado, characterized by hook echo, BWER and deep strong meso-cyclone. The strong echo was slope and extended to 16 km. (4) TDS observed by dual-polarization radar was wide and deep, indicated the tornado process was strong and destructive. Strong ZDR arcs appeared at the head of the hook echo and separated from the strong KDP zone, formed tilt vertical circulation, would promote the development and maintenance of the supercell. Heavy precipitation echo with low centroid appeared in the front of TDS, precipitation and cooling appeared on the ground, and ZDR arcs and ZDR columns weakened and disappeared, and then tornado storm weakened rapidly.
Available online: August 16, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.041101
Abstract:
The forecast of typhoon intensity, especially the rapid intensification (RI) forecast, is still a very challenging problem in current typhoon forecasting. This article is based on the XGBoost model, using NCEP GFS analysis and forecast data from 2015 to 2020, as well as IBTrACS data, to construct RI forecast models (FM) and forecast correction models (FCM) for typhoons in the northwest Pacific for the next 24 hours. Through predictor contribution analysis of the FM model, it was found that the five factors that have the greatest impact on model forecasting are typhoon abundance, average temperature at 200hPa, intensity changes over the past 6 hours, potential intensity, and average divergence at 200hPa. The model was independently tested using data from 2021 to 2022, and the results showed that the FM model had high accuracy when tested using analytical data, with FNR, FPR, and TS of 0.25, 0.24, and 0.32, respectively. However, due to the influence of forecast errors caused by forecast factors, the performance of FM models in real-time forecasting decreases. FCM models constructed using forecast data can effectively correct forecast errors by learning them, thereby reducing the impact of forecast errors. The FNR, FPR, and TS of the FCM model in real-time forecasting tests were 0.28, 0.25, and 0.30, respectively. Compared with the FM model (FNR, FPR, and TS were 0.32, 0.26, and 0.27, respectively), the FNR and FPR decreased by 0.04 and 0.01, and the TS increased by 0.03. The FCM model is convenient and easy to use, providing reference for real-time forecasting of typhoon intensity and typhoon RI.
The forecast of typhoon intensity, especially the rapid intensification (RI) forecast, is still a very challenging problem in current typhoon forecasting. This article is based on the XGBoost model, using NCEP GFS analysis and forecast data from 2015 to 2020, as well as IBTrACS data, to construct RI forecast models (FM) and forecast correction models (FCM) for typhoons in the northwest Pacific for the next 24 hours. Through predictor contribution analysis of the FM model, it was found that the five factors that have the greatest impact on model forecasting are typhoon abundance, average temperature at 200hPa, intensity changes over the past 6 hours, potential intensity, and average divergence at 200hPa. The model was independently tested using data from 2021 to 2022, and the results showed that the FM model had high accuracy when tested using analytical data, with FNR, FPR, and TS of 0.25, 0.24, and 0.32, respectively. However, due to the influence of forecast errors caused by forecast factors, the performance of FM models in real-time forecasting decreases. FCM models constructed using forecast data can effectively correct forecast errors by learning them, thereby reducing the impact of forecast errors. The FNR, FPR, and TS of the FCM model in real-time forecasting tests were 0.28, 0.25, and 0.30, respectively. Compared with the FM model (FNR, FPR, and TS were 0.32, 0.26, and 0.27, respectively), the FNR and FPR decreased by 0.04 and 0.01, and the TS increased by 0.03. The FCM model is convenient and easy to use, providing reference for real-time forecasting of typhoon intensity and typhoon RI.
Available online: August 13, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031801
Abstract:
Based on the detection data of S-band dual-polarization Doppler weather radar in Xinle, Shijiazhuang, conventional meteorological observation data and regional automatic weather station observation data, the evolution characteristics of dual-polarization structure of supercell storm with long life history caused by large hail in central Hebei on June 25,2020 were analyzed. The results show that the supercell storm occurs in a strong thermal instability and strong vertical wind shear environment. The effective growth layer thickness of hailThe effective growth layer thickness of hail is about 3 km and the thickness ratio of cold and warm clouds exceeds 2.3. The height of maximum thermal buoyancy height is located in the effective growth layer, and the intensity of maximum thermal buoyancy intensity is greater than 4 °C, which is conducive to the formation of large hail. In the strong echo center of the low-level supercell storm, large wet ( or dry ) hail coexists with heavy precipitation, and the reflectivity factor exceeds 65 dBz, corresponding to small differential reflectivity and correlation coefficient, and the differential phase shift rate is not displayed in a large range. The large wet ( or dry ) hail in the low-level strong echo center of the supercell storm coexists with heavy precipitation, and the reflectivity factor exceeds 65 dBz. Corresponding to the differential reflectivity and correlation coefficient, the large range of differential phase shift rate is not shown. The strong echo area on the left side of before and after the supercell storm is weak rainfall and a small amount of melted hail. The reflectivity factor is between 50 ~ 55 dBz, and the differential reflectivity is large, the correlation coefficient and the differential phase shift rate are large. The ZDR columnring, CC low value arearing and KDP column in the middle layer of the supercell storm are located on the left and right sides of the bounded weak echo area, and the left CC low value arearing is stronger and located in the center of the strong echoin the strong echo center. Due to the existence of mixed phase and large structural differences, the correlation coefficient is smaller. The right KDP column is stronger and located in the bounded weak echo area. The narrow ZDR column in the upper layer is located on the right edge of the strong echo center, and the CC low value area is located in the the strong echo center center. There is a strong updraft in the strong echo center area and the bounded weak echo area and the strong echo center area in the middle and upper layers. When the large hail falls, the height of CC low value area and CC ring corresponding to the strong echo center decreases rapidly and the intensity decreases obviously. , Tthe ZDR hole expands to the lowest elevation angle and the width increases, which can be used as the basis for judgingcriterion for the imminent landing of large hail. When a large hail falls, the height of the ZDR ring, ZDDR column and CC low value area decreases, and the intensity weakens. However, the ZDR column, ZDR ring and CC low value area in the weak echo area on the right side of the supercell always exist, and the low-level ZDR arc is strengthened, the middle-level rotation is weakened, but the low-level rotation is strengthened, and the strong updraft always exists, so the supercell can maintain for a long time.The height and intensity of the ZDR ring, ZD ring and CC low value area decreased when the large hail fell, but the ZDR ring, ZDR ring and CC were low in the weak echo area on the right side of the supercell.
Based on the detection data of S-band dual-polarization Doppler weather radar in Xinle, Shijiazhuang, conventional meteorological observation data and regional automatic weather station observation data, the evolution characteristics of dual-polarization structure of supercell storm with long life history caused by large hail in central Hebei on June 25,2020 were analyzed. The results show that the supercell storm occurs in a strong thermal instability and strong vertical wind shear environment. The effective growth layer thickness of hail
Available online: August 02, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.080201
Abstract:
The temporal evolution of atmospheric convective boundary layer height (CBLH) has an important impact on weather and climate change, but there are few studies on the CBLH climatology over Beijing area. This study presents the CBLH climatology over Beijing by using high resolution ERA5 reanalysis data for the period 1992 - 2022. The ERA5 CBLH was first evaluated against radiosonde-derived CBLH. ERA5 can reproduced the CBLH variation characteristics by sounding reasonably well. Next, the interannual, seasonal and diurnal variations of the CBLHs, as well as the correlation between the CBLH and key meteorological parameters were analyzed. The results show that in the past 30 years, the CBLH in spring and autumn has decreased at the rate of 61.6 m per decade and 13.1 m per decade, respectively, while that in summer and winter has increased at the rate of 2.9 m per decade and 7.7 m per decade, respectively. The median value of CBLH at noon in spring, summer, autumn, and winter is about 1700 m, 1100 m, 950 m, and 800 m, respectively. The CBLH in spring is the highest among the four seasons, because of the large surface sensible heat flux and the weak atmospheric stability. By analyzing the relationship between CBLH and sensible heat flux, potential temperature lapse rate and Ts-Ta (surface temperature [Ts] and air temperature [Ta] difference), it is found that in spring, when the sensible heat flux increases by 100 W·m-2, the CBLH increases by 615 m. When the potential temperature lapse rate increases by 1 ℃·km-1, the CBLH increases by 1376 m. When the Ts-Ta increases by 1 ℃, the CBLH increases by 175 m.
The temporal evolution of atmospheric convective boundary layer height (CBLH) has an important impact on weather and climate change, but there are few studies on the CBLH climatology over Beijing area. This study presents the CBLH climatology over Beijing by using high resolution ERA5 reanalysis data for the period 1992 - 2022. The ERA5 CBLH was first evaluated against radiosonde-derived CBLH. ERA5 can reproduced the CBLH variation characteristics by sounding reasonably well. Next, the interannual, seasonal and diurnal variations of the CBLHs, as well as the correlation between the CBLH and key meteorological parameters were analyzed. The results show that in the past 30 years, the CBLH in spring and autumn has decreased at the rate of 61.6 m per decade and 13.1 m per decade, respectively, while that in summer and winter has increased at the rate of 2.9 m per decade and 7.7 m per decade, respectively. The median value of CBLH at noon in spring, summer, autumn, and winter is about 1700 m, 1100 m, 950 m, and 800 m, respectively. The CBLH in spring is the highest among the four seasons, because of the large surface sensible heat flux and the weak atmospheric stability. By analyzing the relationship between CBLH and sensible heat flux, potential temperature lapse rate and Ts-Ta (surface temperature [Ts] and air temperature [Ta] difference), it is found that in spring, when the sensible heat flux increases by 100 W·m-2, the CBLH increases by 615 m. When the potential temperature lapse rate increases by 1 ℃·km-1, the CBLH increases by 1376 m. When the Ts-Ta increases by 1 ℃, the CBLH increases by 175 m.
Available online: August 02, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.080101
Abstract:
In order to address the issue of insufficient vertical sampling below a 5° elevation angle and the presence of detection gaps in the VCP21D scanning mode, four new scanning modes, namely VCP12D, VCP212D, VCP215D, and VCP35D, were developed based on the scanning mode of WSR-88D. These new scanning modes were tested using the Yingkou dual-polarization weather radar, and the results are as follows:（1）The sensitivity and data quality of the four new scanning modes are comparable to the current VCP21D operational mode. The capability to suppress ground clutter is also similar, meeting the operational performance requirements. Therefore, these new scanning modes can be applied in operational settings.（2）The severe convective detection modes, VCP12D and VCP212D, provide increased vertical resolution in the lower levels compared to VCP11D. They can obtain more detailed detection data beyond 100 km from the radar. Additionally, the scanning time is reduced from 5 minutes to 4 minutes, resulting in improved detection performance for rapidly developing severe convective storms.（3）The non-severe precipitation mode, VCP215D, increases the number of elevation angles by 6 compared to VCP21D. This allows for more continuous vertical detection products and enables a more complete and detailed representation of echo structure characteristics and storm top heights. The detection time is comparable to the VCP21D mode, demonstrating its superiority.（4）The clear sky mode, VCP35D, has a slightly smaller data coverage range compared to VCP31D, but it offers higher spatiotemporal resolution and exhibits superior detection capabilities.（5） The new scanning modes have increased the maximum non-blur speed. The high-altitude (above 10°) speeds for VCP12D, VCP212D, and VCP215D modes have been raised to 33.36 m/s, the bottom-altitude (0.5°-1.3°) speeds for VCP212Dand VCP215D modes have been raised to 28.47 m/s, while the entire layer speed for VCP35D has been increased to 26.38 m/s.
In order to address the issue of insufficient vertical sampling below a 5° elevation angle and the presence of detection gaps in the VCP21D scanning mode, four new scanning modes, namely VCP12D, VCP212D, VCP215D, and VCP35D, were developed based on the scanning mode of WSR-88D. These new scanning modes were tested using the Yingkou dual-polarization weather radar, and the results are as follows:（1）The sensitivity and data quality of the four new scanning modes are comparable to the current VCP21D operational mode. The capability to suppress ground clutter is also similar, meeting the operational performance requirements. Therefore, these new scanning modes can be applied in operational settings.（2）The severe convective detection modes, VCP12D and VCP212D, provide increased vertical resolution in the lower levels compared to VCP11D. They can obtain more detailed detection data beyond 100 km from the radar. Additionally, the scanning time is reduced from 5 minutes to 4 minutes, resulting in improved detection performance for rapidly developing severe convective storms.（3）The non-severe precipitation mode, VCP215D, increases the number of elevation angles by 6 compared to VCP21D. This allows for more continuous vertical detection products and enables a more complete and detailed representation of echo structure characteristics and storm top heights. The detection time is comparable to the VCP21D mode, demonstrating its superiority.（4）The clear sky mode, VCP35D, has a slightly smaller data coverage range compared to VCP31D, but it offers higher spatiotemporal resolution and exhibits superior detection capabilities.（5） The new scanning modes have increased the maximum non-blur speed. The high-altitude (above 10°) speeds for VCP12D, VCP212D, and VCP215D modes have been raised to 33.36 m/s, the bottom-altitude (0.5°-1.3°) speeds for VCP212Dand VCP215D modes have been raised to 28.47 m/s, while the entire layer speed for VCP35D has been increased to 26.38 m/s.
Available online: August 01, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022102
Abstract:
A total of 184 hail weather cases in Chengde from April to September, 2000 to 2020 are analyzed by means of multi source data including the hail fact, CINRAD\CB weather radar, NCEP FNL reanalysis, and GFS forecast. Firstly, the distribution characteristics and prediction thresholds of relevant environmental parameters such as water vapor, thermal instability, dynamic lift and characteristic height are analyzed with the form of boxplot. And then, the initial optimal threshold values are set according to the results of the boxplot. The hail labels are determined according to the hail observational records or combined reflectivity (CR) greater than or equal to 60 dBZ from April to September 2014 to 2020. The hail labels are matched to the grids of reanalysis data on the basis of the principle of near location and proximity time to construct the training dataset for feature parameter selection, interval segmentation, probability calculation, and models training. Next, five models for 3h, 6h, 9h, 12h and 24h hail potential prediction are established by Bayesian method. The models are test from June to August during 2021 and 2022, and the results suggest that the Bayes-based hail potential prediction models have feasibility in daily weather forecast. The hit rates of all the models are above 90%, and the average CSI score is over 0.4. Differing from the traditional probability and ingredient methods, the based-methods can provide a stronger objective forecast of hail occurrence, which has a certain reference for predicting severe convective weather in mountainous areas. Nevertheless, there are some falsealarms as the spatiotemporal scale of the reanalysis data is much larger than that of severe convective weather, which need to be improved in the future.
A total of 184 hail weather cases in Chengde from April to September, 2000 to 2020 are analyzed by means of multi source data including the hail fact, CINRAD\CB weather radar, NCEP FNL reanalysis, and GFS forecast. Firstly, the distribution characteristics and prediction thresholds of relevant environmental parameters such as water vapor, thermal instability, dynamic lift and characteristic height are analyzed with the form of boxplot. And then, the initial optimal threshold values are set according to the results of the boxplot. The hail labels are determined according to the hail observational records or combined reflectivity (CR) greater than or equal to 60 dBZ from April to September 2014 to 2020. The hail labels are matched to the grids of reanalysis data on the basis of the principle of near location and proximity time to construct the training dataset for feature parameter selection, interval segmentation, probability calculation, and models training. Next, five models for 3h, 6h, 9h, 12h and 24h hail potential prediction are established by Bayesian method. The models are test from June to August during 2021 and 2022, and the results suggest that the Bayes-based hail potential prediction models have feasibility in daily weather forecast. The hit rates of all the models are above 90%, and the average CSI score is over 0.4. Differing from the traditional probability and ingredient methods, the based-methods can provide a stronger objective forecast of hail occurrence, which has a certain reference for predicting severe convective weather in mountainous areas. Nevertheless, there are some falsealarms as the spatiotemporal scale of the reanalysis data is much larger than that of severe convective weather, which need to be improved in the future.
Available online: July 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061401
Abstract:
To study the mesoscale characteristics and causes of extreme short-time heavy rainfall at night in Tianjin，by using encrypted automatic station data, min precipitation data, Doppler weather Radar data, wind profile data and the 5th generation global Atmospheric Reanalysis product (ERA5) of the European Center for Medium-Range Weather Forecasts, an extreme short-time heavy precipitation occurred in Tianjin in the early morning of July 3, 2022 was diagnosed and analyzed. The results show that: There was no significant low-value weather system at 500 hPa and no synoptic low-level jet background at the lower level. It was a rainstorm process mainly caused by small and medium scale forcing under atypical circulation situation, with obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused precipitation was presented in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echo organizations, and its radar echo had a high centroid, showing the characteristics of continental strong convective echo. The enhancement of the 975hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the ground, and synergizing with enhanced instability caused by mid-level dry cold air intrusion, which were the main reason for the triggering of the initial convection. The cold pool formed after precipitation formed a clear and irregular outflow boundary with the ambient wind, and the forcing action of the bottom cold pool led to the formation and development of γ-mesoscale vortex in front of the outflow boundary. The ageostrophic wind rotation caused by the inertial oscillation of the boundary layer at night and the gradually formed inversion stratification made the warm and moist air from the southeast from the sea continuously strengthen into the boundary layer jet, and then caused the vertical wind shear of 0-2.5km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhanced cold pool reached a temporary equilibrium. Resultly, the vortex in front of the outflow boundary continue to strengthened and developed from the bottom to up, and the strong dynamic convergence accompanying the vortex directly leaded to the rapid growth of minute-level rain intensity and lasted for several minutes, which finally leaded to the emergence of extreme short-term heavy precipitation. The results provide a reference basis for predicting local short-time heavy precipitation at night and exploring its occurrence and development mechanism in North China.
To study the mesoscale characteristics and causes of extreme short-time heavy rainfall at night in Tianjin，by using encrypted automatic station data, min precipitation data, Doppler weather Radar data, wind profile data and the 5th generation global Atmospheric Reanalysis product (ERA5) of the European Center for Medium-Range Weather Forecasts, an extreme short-time heavy precipitation occurred in Tianjin in the early morning of July 3, 2022 was diagnosed and analyzed. The results show that: There was no significant low-value weather system at 500 hPa and no synoptic low-level jet background at the lower level. It was a rainstorm process mainly caused by small and medium scale forcing under atypical circulation situation, with obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused precipitation was presented in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echo organizations, and its radar echo had a high centroid, showing the characteristics of continental strong convective echo. The enhancement of the 975hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the ground, and synergizing with enhanced instability caused by mid-level dry cold air intrusion, which were the main reason for the triggering of the initial convection. The cold pool formed after precipitation formed a clear and irregular outflow boundary with the ambient wind, and the forcing action of the bottom cold pool led to the formation and development of γ-mesoscale vortex in front of the outflow boundary. The ageostrophic wind rotation caused by the inertial oscillation of the boundary layer at night and the gradually formed inversion stratification made the warm and moist air from the southeast from the sea continuously strengthen into the boundary layer jet, and then caused the vertical wind shear of 0-2.5km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhanced cold pool reached a temporary equilibrium. Resultly, the vortex in front of the outflow boundary continue to strengthened and developed from the bottom to up, and the strong dynamic convergence accompanying the vortex directly leaded to the rapid growth of minute-level rain intensity and lasted for several minutes, which finally leaded to the emergence of extreme short-term heavy precipitation. The results provide a reference basis for predicting local short-time heavy precipitation at night and exploring its occurrence and development mechanism in North China.
Available online: July 24, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.042003
Abstract:
Abstract: Based on the meteorological data from conventional observation stations, traffic weather stations and high-altitude ground data, a typical large-scale regional heavy fog weather process in Henan Province in spring from the night of March 11 to the day of March 12, 2021 was analyzed. A schematic diagram of the visibility change characteristic curve of this process was summarized and condensed. By analyzing the time characteristics and occurrence and development of the process of heavy fog, the results showed that there were mainly two types of visibility change curves in this heavy fog process. One was to first go through a period of violent fluctuations up and down and finally reached a strong dense fog and maintained it, and the other was to directly and rapidly exploded to form a heavy fog. At most stations,the heavy fog had the characteristics of explosive enhancement. The average action time for visibility to drop from above 1000 m to below 200 m was only 9.5 minutes. The average longest duration of the heavy fog was 193.6 minutes, and the longest was 459 minutes. The average action time of fog elimination was 35 minutes, which was significantly longer than that of explosive enhancement. The high humidity environment formed by the precipitation before the fog provided a good background condition for this heavy fog process. The cooling of the near-surface layer produced by net surface radiation fluxes was the triggering and explosive development mechanism for the fog event. Large-scale breeze (wind speed <1m s-1) or even calm wind near the surface layer was another favorable condition for explosive development of this fog process. At the same time, the near-surface wet advection transport was also an important reason for the explosive development and maintenance of this heavy fog process.
Abstract: Based on the meteorological data from conventional observation stations, traffic weather stations and high-altitude ground data, a typical large-scale regional heavy fog weather process in Henan Province in spring from the night of March 11 to the day of March 12, 2021 was analyzed. A schematic diagram of the visibility change characteristic curve of this process was summarized and condensed. By analyzing the time characteristics and occurrence and development of the process of heavy fog, the results showed that there were mainly two types of visibility change curves in this heavy fog process. One was to first go through a period of violent fluctuations up and down and finally reached a strong dense fog and maintained it, and the other was to directly and rapidly exploded to form a heavy fog. At most stations,the heavy fog had the characteristics of explosive enhancement. The average action time for visibility to drop from above 1000 m to below 200 m was only 9.5 minutes. The average longest duration of the heavy fog was 193.6 minutes, and the longest was 459 minutes. The average action time of fog elimination was 35 minutes, which was significantly longer than that of explosive enhancement. The high humidity environment formed by the precipitation before the fog provided a good background condition for this heavy fog process. The cooling of the near-surface layer produced by net surface radiation fluxes was the triggering and explosive development mechanism for the fog event. Large-scale breeze (wind speed <1m s-1) or even calm wind near the surface layer was another favorable condition for explosive development of this fog process. At the same time, the near-surface wet advection transport was also an important reason for the explosive development and maintenance of this heavy fog process.
Available online: July 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.063002
Abstract:
The Round-trip Drifting Sounding System (RDSS) can realize vertical detection of the atmospheric temperature profile from ground to the lower stratosphere and the continuous 4h horizontal temperature distribution in the lower stratosphere. Round-trip Drifting Sounding observation tests have been carried out in the middle and lower reaches of the Yangtze River, Guangdong, Inner Mongolia and other places, and the results is were very successful. Based on the data of Round-trip Drifting Sounding experiment in the middle and lower reaches of the Yangtze River from March to September 2021, this paper completed the verification of atmospheric humidity profile data of satellite. The results show that: 1)The validation results of the Descending Phase data of the Round-trip Drifting Sounding indicate that the average absolute error of the satellite humidity profile is approximately 15%, and the root mean square error is approximately 20%. 2) At noon and night, the quality of humidity profile data of satellite is better than that in the morning and evening. 3) The humidity error of the satellite decreases with increasing altitude and increases with increasing humidity. 4) Below 50% humidity, the satellite retrieved humidity is relatively large, and above 50% humidity, the satellite retrieved humidity is relatively small.
The Round-trip Drifting Sounding System (RDSS) can realize vertical detection of the atmospheric temperature profile from ground to the lower stratosphere and the continuous 4h horizontal temperature distribution in the lower stratosphere. Round-trip Drifting Sounding observation tests have been carried out in the middle and lower reaches of the Yangtze River, Guangdong, Inner Mongolia and other places, and the results is were very successful. Based on the data of Round-trip Drifting Sounding experiment in the middle and lower reaches of the Yangtze River from March to September 2021, this paper completed the verification of atmospheric humidity profile data of satellite. The results show that: 1)The validation results of the Descending Phase data of the Round-trip Drifting Sounding indicate that the average absolute error of the satellite humidity profile is approximately 15%, and the root mean square error is approximately 20%. 2) At noon and night, the quality of humidity profile data of satellite is better than that in the morning and evening. 3) The humidity error of the satellite decreases with increasing altitude and increases with increasing humidity. 4) Below 50% humidity, the satellite retrieved humidity is relatively large, and above 50% humidity, the satellite retrieved humidity is relatively small.
Available online: July 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.071501
Abstract:
Aerosols and cloud microphysics observational researches have been carried out by aircraft which equipped with cloud physics detection instruments for many years in Hebei Province, China. A series of research results have been obtained and published in the fields of aerosols, cloud condensation nuclei (CCN), clouds and precipitation macro and micro structure characteristics, especially some weather modification catalytic experiments by aircraft. In this paper, the research progress of aerosols and cloud precipitation physical observations over Hebei Province in the recent 20 years were systematically summarized, and the microphysical characteristics of aerosols, CCN and clouds, such as vertical structure, spatial distribution and seasonal variation, were summarized. Four observation field campaigns for aircraft precipitation enhancement operation and the effect test are introduced in detail, and the physical evidence of macro and micro physical characteristics changes in the supercooled water area before and after cloud catalysis is objectively demonstrated. This paper puts forward the future development direction on the basis of summarizing a large number of research results, and provides some suggestions for aerosol-cloud physical aircraft observation and weather modification activities through aircraft catalysis in North China.
Aerosols and cloud microphysics observational researches have been carried out by aircraft which equipped with cloud physics detection instruments for many years in Hebei Province, China. A series of research results have been obtained and published in the fields of aerosols, cloud condensation nuclei (CCN), clouds and precipitation macro and micro structure characteristics, especially some weather modification catalytic experiments by aircraft. In this paper, the research progress of aerosols and cloud precipitation physical observations over Hebei Province in the recent 20 years were systematically summarized, and the microphysical characteristics of aerosols, CCN and clouds, such as vertical structure, spatial distribution and seasonal variation, were summarized. Four observation field campaigns for aircraft precipitation enhancement operation and the effect test are introduced in detail, and the physical evidence of macro and micro physical characteristics changes in the supercooled water area before and after cloud catalysis is objectively demonstrated. This paper puts forward the future development direction on the basis of summarizing a large number of research results, and provides some suggestions for aerosol-cloud physical aircraft observation and weather modification activities through aircraft catalysis in North China.
Available online: July 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.051001
Abstract:
The observation quality of reflectivity of Shenzhen Qiuyutan X-band phased-array radar is quantitatively evaluated by comparing it to Shenzhen Zhuzilin disdrometer data and Shenzhen Qiuyutan S-band radar data. The results suggest that the reflectivity of X-band phased-array radar is highly consistent with the reflectivity retrieved by disdrometer and observed by S-band radar, with correlation coefficients greater than 0.75 and relative mean biases close to 0, which indicates minimal deviation. The X-band phased-array radar also shows stable performance under different rain intensity periods. However, the deviation of reflectivity of X-band phased-array radar is different under different reflectivity intensities. The reflectivity of X-band phased-array radar is positively biased when reflectivity is under 25 dBz, and negatively biased otherwise. As reflectivity intensifies, the degree of the negative bias gradually increases, and the average bias of reflectivity can reach 8-10 dB when reflectivity exceeds 50 dBz.
The observation quality of reflectivity of Shenzhen Qiuyutan X-band phased-array radar is quantitatively evaluated by comparing it to Shenzhen Zhuzilin disdrometer data and Shenzhen Qiuyutan S-band radar data. The results suggest that the reflectivity of X-band phased-array radar is highly consistent with the reflectivity retrieved by disdrometer and observed by S-band radar, with correlation coefficients greater than 0.75 and relative mean biases close to 0, which indicates minimal deviation. The X-band phased-array radar also shows stable performance under different rain intensity periods. However, the deviation of reflectivity of X-band phased-array radar is different under different reflectivity intensities. The reflectivity of X-band phased-array radar is positively biased when reflectivity is under 25 dBz, and negatively biased otherwise. As reflectivity intensifies, the degree of the negative bias gradually increases, and the average bias of reflectivity can reach 8-10 dB when reflectivity exceeds 50 dBz.
Available online: July 10, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.040701
Abstract:
Baihetan Hydroelectric Power Station is located in the canyon area of the lower reaches of the Jinsha River, with frequent northerly windy weather in the dry season. Objectively identifying the circulation system that affects the strong winds of the hydroelectric power station is beneficial for revealing the formation mechanism of strong winds in special areas. Based on 139 cases of northerly windy weather in the dry season in the canyon area from November 2018 to November 2020 to April of the following year,, this paper analyzes the circulation situation of windy weather, and establishes objective identification conditions with reference to the Lamb-Jenkinson (L-J) method,tests and modifies the identification conditions. The following conclusions are obtained:(1) Fifteen typical northerly winds in hydropower stations are selected, and through the analysis of the characteristics of circulation situation, the upper-air circulation affecting the gale is summarized as: southern branch trough, plateau trough and northern transverse trough. In 15 cases, the first two types appeared 6 times each and the transverse groove type appeared 3 times. (2) Based on the analysis of circulation characteristic parameters by L-J method, the key areas and preliminary identification conditions of gale circulation in dry season are determined. The identification conditions of the south branch trough and plateau trough are that the zonal component u of the geostrophic wind in the key area is greater than 10 dagpm·10olongitude-1, and the difference with the meridional component v is greater than dagpm·10olongitude-1, while The?vorticity of the geostrophic wind. is greater than 0 dagpm·10olongitude-1; The identification condition of transverse groove type is that the critical area u is less than 20 dagpm·10olongitude-1,and it is required to be greater than u. (3)In addition, 14 cases of gales in the dry season of 2021 were selected to test the above circulation identification conditions, and it was found that 11 of them accurately identified the circulation type. According to the reason that the circulation type is not recognized, the thresholds of you and the difference between you and v are corrected, and the results show that the corrected discrimination conditions are accurate and feasible. Finally, the objective identification method of circulation situation can provide a reference for gale warning.
Baihetan Hydroelectric Power Station is located in the canyon area of the lower reaches of the Jinsha River, with frequent northerly windy weather in the dry season. Objectively identifying the circulation system that affects the strong winds of the hydroelectric power station is beneficial for revealing the formation mechanism of strong winds in special areas. Based on 139 cases of northerly windy weather in the dry season in the canyon area from November 2018 to November 2020 to April of the following year,, this paper analyzes the circulation situation of windy weather, and establishes objective identification conditions with reference to the Lamb-Jenkinson (L-J) method,tests and modifies the identification conditions. The following conclusions are obtained:(1) Fifteen typical northerly winds in hydropower stations are selected, and through the analysis of the characteristics of circulation situation, the upper-air circulation affecting the gale is summarized as: southern branch trough, plateau trough and northern transverse trough. In 15 cases, the first two types appeared 6 times each and the transverse groove type appeared 3 times. (2) Based on the analysis of circulation characteristic parameters by L-J method, the key areas and preliminary identification conditions of gale circulation in dry season are determined. The identification conditions of the south branch trough and plateau trough are that the zonal component u of the geostrophic wind in the key area is greater than 10 dagpm·10olongitude-1, and the difference with the meridional component v is greater than dagpm·10olongitude-1, while The?vorticity of the geostrophic wind. is greater than 0 dagpm·10olongitude-1; The identification condition of transverse groove type is that the critical area u is less than 20 dagpm·10olongitude-1,and it is required to be greater than u. (3)In addition, 14 cases of gales in the dry season of 2021 were selected to test the above circulation identification conditions, and it was found that 11 of them accurately identified the circulation type. According to the reason that the circulation type is not recognized, the thresholds of you and the difference between you and v are corrected, and the results show that the corrected discrimination conditions are accurate and feasible. Finally, the objective identification method of circulation situation can provide a reference for gale warning.
Available online: July 08, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.070301
Abstract:
The wind field observation play an important role in the weather research and forecasting. The IVAP technique which is based on the azimuth uniform assumption retrieval relationship, offers good compatibility and practical simplicity for 2-D wind field retrieval. This paper selected the large-scale precipitation event from July to August 2020, established the wind fields based on the operational Doppler radar network using the IVAP technique, and used the secondly radiosonde data as a reference to conduct a quality assessment and analysis of the retrieved wind fields. The results indicate that: retrieved wind fields of Doppler radar network have high correlation with radiosonde data, and the quality of wind direction is better than the wind speed on higher altitude. The quality of the retrieved winds are better in the areas with precipitation than non-precipitation areas. The quality is worst in clear sky areas, especially when the altitude is higher than 4 km. The retrieved winds of a scattered precipitation event on 6 July 2019 demonstrate that the vortex structure, shear line and other dynamic field characteristics were captured. This study shows that based on the single Doppler radar wind retrieval, the IVAP technique has the ability to retrieve wind fields of Doppler radar network. This method has good application prospect in practical operations, and can provide a better basis for weather forecasting services as well as wind field data assimilation.
The wind field observation play an important role in the weather research and forecasting. The IVAP technique which is based on the azimuth uniform assumption retrieval relationship, offers good compatibility and practical simplicity for 2-D wind field retrieval. This paper selected the large-scale precipitation event from July to August 2020, established the wind fields based on the operational Doppler radar network using the IVAP technique, and used the secondly radiosonde data as a reference to conduct a quality assessment and analysis of the retrieved wind fields. The results indicate that: retrieved wind fields of Doppler radar network have high correlation with radiosonde data, and the quality of wind direction is better than the wind speed on higher altitude. The quality of the retrieved winds are better in the areas with precipitation than non-precipitation areas. The quality is worst in clear sky areas, especially when the altitude is higher than 4 km. The retrieved winds of a scattered precipitation event on 6 July 2019 demonstrate that the vortex structure, shear line and other dynamic field characteristics were captured. This study shows that based on the single Doppler radar wind retrieval, the IVAP technique has the ability to retrieve wind fields of Doppler radar network. This method has good application prospect in practical operations, and can provide a better basis for weather forecasting services as well as wind field data assimilation.
Available online: July 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061801
Abstract:
To study the causes for rapid weakening and dissipation of Typhoon Bavi(2008) after its landfall in the north , a numerical simulation was carried out using the non-hydrostatic mesoscal model WRF(Weather Research Forecast) , and the simulated results were verified by the observation data. Furthermore, based on the high-resolution simulation results, the weather circulation background and the characteristics of environmental field change were analyzed before and after the landfall of Bavi. The results indicate that the simulated track, intensity change and precipitation distribution of Bavi all matched with the observations well before and its landfall. Bavi was guided by the southwestly airflow in front of the mid-latitude westerly trough, and was located on the right side of the upper-level jet entrance area before its landfall, the divergence field at upper levels was conducive to maintaining the typhoon circulation. After Bavi made landfall, on the one hand, the reduction of the upper-level jet on the north side of typhoon and the weakening of the upper-level divergence inhibited the development of typhoon convection; on the other hand, the sinking strong cold air invaded into the center of typhoon from the northeast side of the low level, which destroyed the vertical warm-core structure of Bavi, then the height was reduced and inclined to the east. In addition, the strong vertical wind shear, especially from middle to up levels, was unfavorable for typhoon sustention, and the lack of water vapor supply is another reason for the rapid weakening and disappearance of the typhoon after its landfall.
To study the causes for rapid weakening and dissipation of Typhoon Bavi(2008) after its landfall in the north , a numerical simulation was carried out using the non-hydrostatic mesoscal model WRF(Weather Research Forecast) , and the simulated results were verified by the observation data. Furthermore, based on the high-resolution simulation results, the weather circulation background and the characteristics of environmental field change were analyzed before and after the landfall of Bavi. The results indicate that the simulated track, intensity change and precipitation distribution of Bavi all matched with the observations well before and its landfall. Bavi was guided by the southwestly airflow in front of the mid-latitude westerly trough, and was located on the right side of the upper-level jet entrance area before its landfall, the divergence field at upper levels was conducive to maintaining the typhoon circulation. After Bavi made landfall, on the one hand, the reduction of the upper-level jet on the north side of typhoon and the weakening of the upper-level divergence inhibited the development of typhoon convection; on the other hand, the sinking strong cold air invaded into the center of typhoon from the northeast side of the low level, which destroyed the vertical warm-core structure of Bavi, then the height was reduced and inclined to the east. In addition, the strong vertical wind shear, especially from middle to up levels, was unfavorable for typhoon sustention, and the lack of water vapor supply is another reason for the rapid weakening and disappearance of the typhoon after its landfall.
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.1000-0526.2024.040801
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 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: 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.
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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．
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.
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.
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).
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(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
Abstract:
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
Abstract:
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
Abstract:
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
ZHANG Xiaoling, ZHANG Tao, LIU Xinhua, ZHOU Qingliang, CHEN Yun, ZHOU Xiaoxia, ZHENG Yongguang, ZHAO Surong
2010,36(7):143-150, DOI: 10.7519/j.issn.1000-0526.2010.7.021
Abstract:
Mesoscale severe weather forecasting ability is limited, in some sense for a lack of valid analysis on mesoscale convective systems and its favorable environments. This paper introduces the mesoscale weather chart analysis techniq ue which was tested in the National Meteorological Center (NMC). Mesoscale weath er chart analyzes the favorable environmental conditions of mesoscale convective systems based on observational data and numerical weather forecast outputs. It includes upper air composite chart and surface chart. In the upper air composite ch art, by analyzing wind, temperature, moisture, temperature change and height change, the diagnostic systems and features in all the lower, middle and upper t roposphere isobaric layers are combined into one plot, which can clearly displa y the available environments and synoptic pattern of severe convective weather. In the surface chart, the analysis contents are pressure, wind, temperature, moi sture, convective weather phenomena and all kinds of boundaries (fronts). The te st in NMC shows that mesoscale weather chart analysis is a dependable means for severe convective weather outlook forecasting.
Mesoscale severe weather forecasting ability is limited, in some sense for a lack of valid analysis on mesoscale convective systems and its favorable environments. This paper introduces the mesoscale weather chart analysis techniq ue which was tested in the National Meteorological Center (NMC). Mesoscale weath er chart analyzes the favorable environmental conditions of mesoscale convective systems based on observational data and numerical weather forecast outputs. It includes upper air composite chart and surface chart. In the upper air composite ch art, by analyzing wind, temperature, moisture, temperature change and height change, the diagnostic systems and features in all the lower, middle and upper t roposphere isobaric layers are combined into one plot, which can clearly displa y the available environments and synoptic pattern of severe convective weather. In the surface chart, the analysis contents are pressure, wind, temperature, moi sture, convective weather phenomena and all kinds of boundaries (fronts). The te st in NMC shows that mesoscale weather chart analysis is a dependable means for severe convective weather outlook forecasting.
2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
Abstract:
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
2013,39(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.
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.
2014,40(4):400-411, DOI: 10.7519/j.issn.1000-0526.2014.04.002
Abstract:
Based on the synoptic environment analysis of about 100 severe convection cases in China since 2000 and the reference of related literatures, from the perspectives of the three essential conditions for the development of severe convection, namely the thermal instability, lift and moisture, five basic synoptic situation configurations of severe convection in China are proposed and expounded. They are cold advection forcing category, warm advection forcing category, baroclinic frontogenesis category, quasi barotropic category and elevated thunderstorm category. The typical characteristics of the upper cold advection forcing category is that the mid upper strong cold advection above 500 hPa strengthens and reaches the boundary warm convergence zone. The warm advection forcing category is characterized by trough with special structure moving over low level strong warm and moist advection. The deep convection produced by the mid lower layer convergence of cold and warm air features the baroclinic frontogenesis category. The quasi barotropic category mostly occurs at the northern and the southern edges or the interior of summer subtropical high and the area with weak baroclinicity, where the dynamic forcing and the surface inhomogeneous local heating play major roles. The features of elevated thunderstorms are the southwest jet in 700-500 hPa lifted by boundary cold wedge and the instable energy is from above 700 hPa. The classification based on the difference of the formation mechanisms can grasp accurately the synoptic characteristics, the situation configurations, the dynamic and thermal properties and the key points in analyzing short term potential forecast, providing more technical support to further enhance the level of weather prediction.
Based on the synoptic environment analysis of about 100 severe convection cases in China since 2000 and the reference of related literatures, from the perspectives of the three essential conditions for the development of severe convection, namely the thermal instability, lift and moisture, five basic synoptic situation configurations of severe convection in China are proposed and expounded. They are cold advection forcing category, warm advection forcing category, baroclinic frontogenesis category, quasi barotropic category and elevated thunderstorm category. The typical characteristics of the upper cold advection forcing category is that the mid upper strong cold advection above 500 hPa strengthens and reaches the boundary warm convergence zone. The warm advection forcing category is characterized by trough with special structure moving over low level strong warm and moist advection. The deep convection produced by the mid lower layer convergence of cold and warm air features the baroclinic frontogenesis category. The quasi barotropic category mostly occurs at the northern and the southern edges or the interior of summer subtropical high and the area with weak baroclinicity, where the dynamic forcing and the surface inhomogeneous local heating play major roles. The features of elevated thunderstorms are the southwest jet in 700-500 hPa lifted by boundary cold wedge and the instable energy is from above 700 hPa. The classification based on the difference of the formation mechanisms can grasp accurately the synoptic characteristics, the situation configurations, the dynamic and thermal properties and the key points in analyzing short term potential forecast, providing more technical support to further enhance the level of weather prediction.
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