ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,Issue 8,2024 Table of Contents
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.
WENG Zhimei
,
LI Yuan
,
FAN Minshuang
,
GAO Li
,
FENG Yecheng
,
WANG Kai
,
NI Zhongping
,
HUANG Xiaolong
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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ISSN:1000-0526 CN:11-2282/P