ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 48,Issue 5,2022 Table of Contents
2022, 48(5):533-544.
DOI: 10.7519/j.issn.1000-0526.2021.122902
Abstract:
In mid-late July 2021, an extreme heavy rainfall process with the characteristics of long duration, large accumulated rainfall amount, and concentrated precipitation area occurred in Henan Province, causing serious casualties. Based on automatic station rainfall data and ERA5 reanalysis data, the important functions and influence mechanisms of multiscale system, jet and topography on the transport and convergence of water vapor and the formation of precipitation are discussed in this paper. It is found that the severe torrential rain occurred in the favorable circulation conditions with long-distance typhoon (In-fa). A large amount of water vapor coming from the western Pacific penetrated the east border of Henan Province from lower layer, while the water vapor from the South China Sea entered Henan Province from the south side mainly in the middle-low layers of troposphere, resulting in the extreme heavy rainfall under the joint influence of cyclonic vortex, shear line and convergence line. The centers of water vapor convergence and ascending motion in lower layers were caused by the coupling impact of low-level jet and boundary layer jet. In addition, the terrain here played the roles of dinamically blooking and lifting, and thermodynamically lifting at the same time. Besides, combined with the jet, topography made the severe precipitation present as a band shape in front of the mountain, and located in the central part on the 20th July and in the northern part of Henan Province on 21 July 2021.
In mid-late July 2021, an extreme heavy rainfall process with the characteristics of long duration, large accumulated rainfall amount, and concentrated precipitation area occurred in Henan Province, causing serious casualties. Based on automatic station rainfall data and ERA5 reanalysis data, the important functions and influence mechanisms of multiscale system, jet and topography on the transport and convergence of water vapor and the formation of precipitation are discussed in this paper. It is found that the severe torrential rain occurred in the favorable circulation conditions with long-distance typhoon (In-fa). A large amount of water vapor coming from the western Pacific penetrated the east border of Henan Province from lower layer, while the water vapor from the South China Sea entered Henan Province from the south side mainly in the middle-low layers of troposphere, resulting in the extreme heavy rainfall under the joint influence of cyclonic vortex, shear line and convergence line. The centers of water vapor convergence and ascending motion in lower layers were caused by the coupling impact of low-level jet and boundary layer jet. In addition, the terrain here played the roles of dinamically blooking and lifting, and thermodynamically lifting at the same time. Besides, combined with the jet, topography made the severe precipitation present as a band shape in front of the mountain, and located in the central part on the 20th July and in the northern part of Henan Province on 21 July 2021.
2022, 48(5):545-555.
DOI: 10.7519/j.issn.1000-0526.2022.021802
Abstract:
Extreme rainstorms struck Henan Province during 17 to 22 July 2021. With the enhancing of the upper tropospheric cold low (UTCL) over the China East Sea, the precipitation in Henan burst almost simultaneously, indicating that UTCL has potential impact on the development of the precipitation. From 19 to 22 July, the upper-level short-wave trough over Hetao Area, the high ridge over Huanghuai Region, UTCL and the blocking high over Japan Sea formed a wave train which led to the almost stationary synoptic circulations. During the heavy rainfall, UTCL stagnated over the eastern seas of China, resulting in large-scale divergence in westerly jet over Henan Provice and its eastern region. The establishment and enhancement of the upper-level divergence over Henan was clearly related to the acceleration of northwest jet on the west part of UTCL. Meanwhile, south flow jet on the eastside of UTCL enhanced the upper-level outflows of Typhoon In-fa, which was conducive to the growth of In-fa’s circulation and the water vapor transportation to the rainstorm area of Henan. On the other hand, the upper-level sinking caused by UTCL enhanced the stability of the subtropical high, and also enhanced the low-level water vapor transportation from the East China Sea to Henan. The UTCL showed obvious forecast uncertainty. From adjacent forecast cycles, the center of UTCL continued to adjust to the north, intensifying and the heavy rainfall area in Henan also tended to adjust to the east direction. The comparison between strong and weak UTCL circulation among ensemble members shows that, strong UTCL circulation was conducive to enhance the anticyclonic divergent outflow over Henan and was more conducive to the enhancement of precipitation in Henan, which has been also proved by ensemble sensitivity analysis.
Extreme rainstorms struck Henan Province during 17 to 22 July 2021. With the enhancing of the upper tropospheric cold low (UTCL) over the China East Sea, the precipitation in Henan burst almost simultaneously, indicating that UTCL has potential impact on the development of the precipitation. From 19 to 22 July, the upper-level short-wave trough over Hetao Area, the high ridge over Huanghuai Region, UTCL and the blocking high over Japan Sea formed a wave train which led to the almost stationary synoptic circulations. During the heavy rainfall, UTCL stagnated over the eastern seas of China, resulting in large-scale divergence in westerly jet over Henan Provice and its eastern region. The establishment and enhancement of the upper-level divergence over Henan was clearly related to the acceleration of northwest jet on the west part of UTCL. Meanwhile, south flow jet on the eastside of UTCL enhanced the upper-level outflows of Typhoon In-fa, which was conducive to the growth of In-fa’s circulation and the water vapor transportation to the rainstorm area of Henan. On the other hand, the upper-level sinking caused by UTCL enhanced the stability of the subtropical high, and also enhanced the low-level water vapor transportation from the East China Sea to Henan. The UTCL showed obvious forecast uncertainty. From adjacent forecast cycles, the center of UTCL continued to adjust to the north, intensifying and the heavy rainfall area in Henan also tended to adjust to the east direction. The comparison between strong and weak UTCL circulation among ensemble members shows that, strong UTCL circulation was conducive to enhance the anticyclonic divergent outflow over Henan and was more conducive to the enhancement of precipitation in Henan, which has been also proved by ensemble sensitivity analysis.
2022, 48(5):556-570.
DOI: 10.7519/j.issn.1000-0526.2022.032501
Abstract:
This paper analyzes the extreme rainstorm that occurred in Henan Province in 17-22 July 2021 based on the observations from radiosonde, automatic weather stations, Doppler weather radars, and the ECMWF ERA5 reanalysis data. The results show that this process had the characteristics of persistence, extreme rainstorm intensity and obvious topographic precipitation. The extreme rainstorm happened under the stable large-scale synoptic situation. When the high pressure in the Sea of Japan extended westward, and typhoons In-fa and Cempaka moved northwestward, the southwesterly/westerly airflow which strengthened northward in the periphery of the Huanghuai vortex provided abundant water vapor and energy for the occurrence of the extreme rainstorm. The warm-wet advection forcing in the mid-low troposphere, strong convergence and uplift under terrain influence as well as weak north low-level cold air were the important conditions of the extreme rainstorm, and the transformation of the “strong-weak-strong-weak” convective unstable characteristics indicated that there were two complementary physical mechanisms during the extreme heavy precipitation. The morphological structure and evolution characteristics were different in various stages of extreme heavy precipitation convection system (hourly precipitation ≥ 50 mm). In vertical direction, convective systems (CSs) of the short-time heavy precipitation showed the characteristics of low-mass center (stronger than 55 dBz), stretching thickness of the echoes greater than 50 dBz over 5 km, duration over 90-120 minutes. Short-time heavy precipitation CSs developed backward clearly within about 30 km in front of Taihang Mountains. Continuous southward extension of the topographic convergence line formed by the westerly easterly/northeasterly wind around Taihang Mountains was one aspect, and on the other hand further development of the northerly wind before the mountain due to the cold pool effect of heavy precipitation works too.
This paper analyzes the extreme rainstorm that occurred in Henan Province in 17-22 July 2021 based on the observations from radiosonde, automatic weather stations, Doppler weather radars, and the ECMWF ERA5 reanalysis data. The results show that this process had the characteristics of persistence, extreme rainstorm intensity and obvious topographic precipitation. The extreme rainstorm happened under the stable large-scale synoptic situation. When the high pressure in the Sea of Japan extended westward, and typhoons In-fa and Cempaka moved northwestward, the southwesterly/westerly airflow which strengthened northward in the periphery of the Huanghuai vortex provided abundant water vapor and energy for the occurrence of the extreme rainstorm. The warm-wet advection forcing in the mid-low troposphere, strong convergence and uplift under terrain influence as well as weak north low-level cold air were the important conditions of the extreme rainstorm, and the transformation of the “strong-weak-strong-weak” convective unstable characteristics indicated that there were two complementary physical mechanisms during the extreme heavy precipitation. The morphological structure and evolution characteristics were different in various stages of extreme heavy precipitation convection system (hourly precipitation ≥ 50 mm). In vertical direction, convective systems (CSs) of the short-time heavy precipitation showed the characteristics of low-mass center (stronger than 55 dBz), stretching thickness of the echoes greater than 50 dBz over 5 km, duration over 90-120 minutes. Short-time heavy precipitation CSs developed backward clearly within about 30 km in front of Taihang Mountains. Continuous southward extension of the topographic convergence line formed by the westerly easterly/northeasterly wind around Taihang Mountains was one aspect, and on the other hand further development of the northerly wind before the mountain due to the cold pool effect of heavy precipitation works too.
2022, 48(5):571-579.
DOI: 10.7519/j.issn.1000-0526.2021.111201
Abstract:
Based on the hourly precipitation data of 2 373 national and regional stations from China Meteorological Administration, the extreme characteristics of accumulated precipitation, precipitation intensity and time evolution during the “21·7” (17-22 July 2021) severe torrential rain in Henan Province are analyzed. The results show that this torrential rain process had the characteristics of long duration, large accumulated rainfall, strong abruptness and concentrated torrential rain area. The average accumulated precipitation within 6 days reached 219.05 mm per station, and exceeded 600 mm at 155 stations. There were about 5.43×104 km2 in Henan Province where the cumulative process rainfall was more than 250 mm, larger than that (3.45×104 km2) in the “75·8” （August 1975） process. Three periods of extremely heavy precipitation were from 15:00 BT 18 to 04:00 BT 19， from 09:00 BT 19 to 08:00 BT 21, and from 09:00 BT 21 to 14:00 BT 22 July 2021. The maximum precipitation period occurred from 19 to 21 July, and the rainfall falling area was concentrated in the southeast of Taihang Mountain and northeast of Funiu Mountain. 1 514 stations had at least one time of flash heavy rain (≥ 20 mm·h-1), the large value centers were located in Zhengzhou, Xinxiang and Hebi respectively, with the contribution rate of flash heavy rain in some regions exceeding 70%. The severe precipitation center moved from the central part to northen part of Henan Province from noon of 20 July to the night of the 21 July, and the intensity changed from strong to weak and to strong again. The extremity of the rainstorm process shows obvious local characteristics. The hourly rainfall of Zhengzhou Station at 17:00 BT 20 July was 201.9 mm, exceeding the hourly rainfall intensity of the “75·8” process, and breaking the historical record among the national stations. The maximum rainfall intensity within 3 h and 6 h both occurred at Jiangang Reservoir in Zhengzhou. The total precipitation of Zhengzhou Station in July was 902.0 mm, which is nearly 6 times of the historical average in recent 70 years.
Based on the hourly precipitation data of 2 373 national and regional stations from China Meteorological Administration, the extreme characteristics of accumulated precipitation, precipitation intensity and time evolution during the “21·7” (17-22 July 2021) severe torrential rain in Henan Province are analyzed. The results show that this torrential rain process had the characteristics of long duration, large accumulated rainfall, strong abruptness and concentrated torrential rain area. The average accumulated precipitation within 6 days reached 219.05 mm per station, and exceeded 600 mm at 155 stations. There were about 5.43×104 km2 in Henan Province where the cumulative process rainfall was more than 250 mm, larger than that (3.45×104 km2) in the “75·8” （August 1975） process. Three periods of extremely heavy precipitation were from 15:00 BT 18 to 04:00 BT 19， from 09:00 BT 19 to 08:00 BT 21, and from 09:00 BT 21 to 14:00 BT 22 July 2021. The maximum precipitation period occurred from 19 to 21 July, and the rainfall falling area was concentrated in the southeast of Taihang Mountain and northeast of Funiu Mountain. 1 514 stations had at least one time of flash heavy rain (≥ 20 mm·h-1), the large value centers were located in Zhengzhou, Xinxiang and Hebi respectively, with the contribution rate of flash heavy rain in some regions exceeding 70%. The severe precipitation center moved from the central part to northen part of Henan Province from noon of 20 July to the night of the 21 July, and the intensity changed from strong to weak and to strong again. The extremity of the rainstorm process shows obvious local characteristics. The hourly rainfall of Zhengzhou Station at 17:00 BT 20 July was 201.9 mm, exceeding the hourly rainfall intensity of the “75·8” process, and breaking the historical record among the national stations. The maximum rainfall intensity within 3 h and 6 h both occurred at Jiangang Reservoir in Zhengzhou. The total precipitation of Zhengzhou Station in July was 902.0 mm, which is nearly 6 times of the historical average in recent 70 years.
2022, 48(5):580-594.
DOI: 10.7519/j.issn.1000-0526.2021.101801
Abstract:
Based on the 3 h densely-observed radiosonde data from Baolian Station, Chaoyang Station, and Daxing Station in Beijing from 28 August to 2 September 2016, and using the WRF V3.9.1 model and WRF-3DVar system, a numerical simulation test of the atmospheric boundary layer in the Beijing Area was carried out to study the impact of the densely-observed radiosonde data assimilation on the numerical simulation of the boundary layer. The results show that the analysis field formed by assimilation is closer to the observation than the background field, and it can better represent the thermal, humidity and dynamic characteristics of the real atmosphere in the boundary layer. Respectively compared with the background field, the root mean square errors of the analysis field of potential temperature, specific humidity, zonal wind, meridional wind, and wind speed are reduced by 86%, 59%, 24%, 44%, 19% correspondingly, showing a strong correction effect of assimilation. The prediction effect of the densely-observed radiosonde data assimilation within 6 hours of model integration is the best, but gradually weakens in size and scope after 6 hours. The densely-observed radiosonde data assimilation improves the atmospheric humidity in the boundary layer throughout the forecast period. The improvement of the atmospheric thermal state in the boundary layer lasts for 6 hours. For the atmospheric dynamic characteristics in the boundary layer, the zonal wind improves most, the meridional wind and wind speed are not obvious, which are related to the nature of the wind and the complex terrain of Beijing. In addition, the relatively small number of sites for densely-observed radiosonde data in the spatial horizontal direction is one of the reasons that the assimilation effect has a significant improvement in the analysis field but is difficult to last for a long time.
Based on the 3 h densely-observed radiosonde data from Baolian Station, Chaoyang Station, and Daxing Station in Beijing from 28 August to 2 September 2016, and using the WRF V3.9.1 model and WRF-3DVar system, a numerical simulation test of the atmospheric boundary layer in the Beijing Area was carried out to study the impact of the densely-observed radiosonde data assimilation on the numerical simulation of the boundary layer. The results show that the analysis field formed by assimilation is closer to the observation than the background field, and it can better represent the thermal, humidity and dynamic characteristics of the real atmosphere in the boundary layer. Respectively compared with the background field, the root mean square errors of the analysis field of potential temperature, specific humidity, zonal wind, meridional wind, and wind speed are reduced by 86%, 59%, 24%, 44%, 19% correspondingly, showing a strong correction effect of assimilation. The prediction effect of the densely-observed radiosonde data assimilation within 6 hours of model integration is the best, but gradually weakens in size and scope after 6 hours. The densely-observed radiosonde data assimilation improves the atmospheric humidity in the boundary layer throughout the forecast period. The improvement of the atmospheric thermal state in the boundary layer lasts for 6 hours. For the atmospheric dynamic characteristics in the boundary layer, the zonal wind improves most, the meridional wind and wind speed are not obvious, which are related to the nature of the wind and the complex terrain of Beijing. In addition, the relatively small number of sites for densely-observed radiosonde data in the spatial horizontal direction is one of the reasons that the assimilation effect has a significant improvement in the analysis field but is difficult to last for a long time.
2022, 48(5):595-604.
DOI: 10.7519/j.issn.1000-0526.2021.051901
Abstract:
The Fengyun-2H （FY-2H） satellite was successfully launched on 5 June 2018 and the operation is stable ever since. The scanning radiometer VISSR-2 (stretched visible and infrared spin scan radiometer) on-board can provide high spatio-temporal resolution atmospheric TPW (total precipitable water) products. Based on the split window algorithm, FY-2H VISSR TPW performs inversion by adding a 6.9 μm channel.This article uses the water vapor products generated by the radiosonde in 2019 to evaluate the quality of the FY-2H TPW product from the two aspects of product accuracy and stability. Compared with the global sounding data of the first seven days of each month in January, April, July, and October 2019, the root mean square error (RMSE) of FY-2H TPW is 4.92 mm, and the correlation coefficient reaches 0.96.The relative error is within 20%, and the data accuracy is high not only during the daytime, but also at night. The standard deviation of the monthly RMSE of FY-2H TPW products relative to sounding data from January to December 2019 is 0.68 mm, indicating that FY-2H TPW products are relatively stable during the inspection period. Based on the analysis and synthesis of the monthly average TPW products, FY-2H TPW can correctly reflect the distribution of atmospheric precipitation in the Belt and Road Region. According to the above results, the FY-2H VISSR TPW product has high precision and stable quality, and has the application ability to be invested in the Belt and Road area.
The Fengyun-2H （FY-2H） satellite was successfully launched on 5 June 2018 and the operation is stable ever since. The scanning radiometer VISSR-2 (stretched visible and infrared spin scan radiometer) on-board can provide high spatio-temporal resolution atmospheric TPW (total precipitable water) products. Based on the split window algorithm, FY-2H VISSR TPW performs inversion by adding a 6.9 μm channel.This article uses the water vapor products generated by the radiosonde in 2019 to evaluate the quality of the FY-2H TPW product from the two aspects of product accuracy and stability. Compared with the global sounding data of the first seven days of each month in January, April, July, and October 2019, the root mean square error (RMSE) of FY-2H TPW is 4.92 mm, and the correlation coefficient reaches 0.96.The relative error is within 20%, and the data accuracy is high not only during the daytime, but also at night. The standard deviation of the monthly RMSE of FY-2H TPW products relative to sounding data from January to December 2019 is 0.68 mm, indicating that FY-2H TPW products are relatively stable during the inspection period. Based on the analysis and synthesis of the monthly average TPW products, FY-2H TPW can correctly reflect the distribution of atmospheric precipitation in the Belt and Road Region. According to the above results, the FY-2H VISSR TPW product has high precision and stable quality, and has the application ability to be invested in the Belt and Road area.
2022, 48(5):605-617.
DOI: 10.7519/j.issn.1000-0526.2022.012801
Abstract:
The two extreme torrential rain， in the warm area before the cold front on 7 May 2018 and the South China monsoon trough torrential rain without cold air on 29 August 2018, were generated in the coastal linear mesoscale convective system (MCS) in Guangdong and Southern Fujian. After comparative analysis of the environmental background and the characteristics of the convective system， the main conclusions are presented as follows. In both cases, there were obvious 850 hPa and 925 hPa low-level jets. During the torrential rain on 7 May, the middle and lower troposphere had obvious unstable conditions. The significant baroclinic atmosphere, relatively high CAPE value， medium to strong 0-6 km deep vertical wind shear and the obvious dry layer in the middle troposphere were conducive to heavy rainfall and thunderstorm. On 29 August, the conditions were only weak instability, quasi-barotropic atmosphere, higher melting layer height, relatively low CAPE value, weaker 0-6 km deep vertical wind shear and high relative humidity across vertical layers, which were very conducive to heavy rainfall rather than thunderstorm gale. The mean winds in storm bearing layer of the two processes were both from the southwest, and the advection in the former was much stronger than that in the latter. The heavy rain in Xiamen and its surrounding Southern Fujian area was caused by backward propagation, which caused a number of strong convective rain masses to move over the same area and forming heavy rain. The backward propagation on 7 May was caused by the gust front of one convective rain mass meeting with the horizontal convective roll behind another convective rain mass, triggering a new convection. The new convection came from the land. In the case on 29 August, the warm and humid air flow in the lower layer met the gust front behind the mature convective rain mass, triggering a new convection. The new convection was located at sea and continued to move onto the land. Both the ice-phase process and the warm cloud process played a strong role in the convective system on 7 May, while the convective system warm cloud precipitation dominated on 29 August. During the two torrential rains， the meso-γ scale vortex formed near the gust front in the front of the cold pool of the convective system, and combined with the convergence and upward motion of the gust front, produced a positive vertical helicity, which was beneficial to the maintenance of the convective system. The low-level jet, through its transport of water vapor and heat, interaction with topography and cold pools of the convective system, played an important role in the maintenance of the coastal linear MCS.
The two extreme torrential rain， in the warm area before the cold front on 7 May 2018 and the South China monsoon trough torrential rain without cold air on 29 August 2018, were generated in the coastal linear mesoscale convective system (MCS) in Guangdong and Southern Fujian. After comparative analysis of the environmental background and the characteristics of the convective system， the main conclusions are presented as follows. In both cases, there were obvious 850 hPa and 925 hPa low-level jets. During the torrential rain on 7 May, the middle and lower troposphere had obvious unstable conditions. The significant baroclinic atmosphere, relatively high CAPE value， medium to strong 0-6 km deep vertical wind shear and the obvious dry layer in the middle troposphere were conducive to heavy rainfall and thunderstorm. On 29 August, the conditions were only weak instability, quasi-barotropic atmosphere, higher melting layer height, relatively low CAPE value, weaker 0-6 km deep vertical wind shear and high relative humidity across vertical layers, which were very conducive to heavy rainfall rather than thunderstorm gale. The mean winds in storm bearing layer of the two processes were both from the southwest, and the advection in the former was much stronger than that in the latter. The heavy rain in Xiamen and its surrounding Southern Fujian area was caused by backward propagation, which caused a number of strong convective rain masses to move over the same area and forming heavy rain. The backward propagation on 7 May was caused by the gust front of one convective rain mass meeting with the horizontal convective roll behind another convective rain mass, triggering a new convection. The new convection came from the land. In the case on 29 August, the warm and humid air flow in the lower layer met the gust front behind the mature convective rain mass, triggering a new convection. The new convection was located at sea and continued to move onto the land. Both the ice-phase process and the warm cloud process played a strong role in the convective system on 7 May, while the convective system warm cloud precipitation dominated on 29 August. During the two torrential rains， the meso-γ scale vortex formed near the gust front in the front of the cold pool of the convective system, and combined with the convergence and upward motion of the gust front, produced a positive vertical helicity, which was beneficial to the maintenance of the convective system. The low-level jet, through its transport of water vapor and heat, interaction with topography and cold pools of the convective system, played an important role in the maintenance of the coastal linear MCS.
2022, 48(5):618-632.
DOI: 10.7519/j.issn.1000-0526.2021.110801
Abstract:
Based on conventional observation data, Doppler weather radar data and wind profile radar data, a rare severe hailstorm event (1-3 cm in diameter) in Southwest Hubei at the end of winter is analyzed in detail. The results show that the severe hailstorm was produced under the circulation background of upper cold-dry and lower warm-wet and low-altitude convergence and high-altitude divergence. Convective weather was triggered by mesoscale convergence on the ground with favourable terrain at the trumpet and intensified by cold front. Strong vertical wind shear in the lower level was favorable for the formed convective strong storm to maintain and strengthen. The severe hails were produced by isolated supercells and dominant supercells in multicells. In comparison, the isolated supercells were larger and persisted longer. The structures of the supercells reflected typical features such as mesocyclone， high mass center, low-level inflow, weak echo zone and echo drape, middle-level radial convergence and storm-top divergence, etc. The vertically integrated liquid （VIL） and the VIL density maintained high above 35 kg·m-2 and 4 g ·m-3 for a long time in the winter. The hail index of radar algorithm predicts the severe hail with high probability. This process occurred at the end of winter. The typical storm structure showed up after the emergence of convection, and the early warning of hail could be made 10-30 minutes in advance. However, for the short-time potential forecast of severe hail several hours in advance before the occurrence of severe convection, the key parameters (such as CAPE， 0-6 km vertical wind shear and melting layer height) for judging the potential of severe hail are not typical, which will mislead forecasters to ignore the hail potential judgment. Forecasters need to be extremely cautious and do in-depth analysis when conducting potential analysis of severe convective weather in this environmental background, so as to obtain correct forecast results.
Based on conventional observation data, Doppler weather radar data and wind profile radar data, a rare severe hailstorm event (1-3 cm in diameter) in Southwest Hubei at the end of winter is analyzed in detail. The results show that the severe hailstorm was produced under the circulation background of upper cold-dry and lower warm-wet and low-altitude convergence and high-altitude divergence. Convective weather was triggered by mesoscale convergence on the ground with favourable terrain at the trumpet and intensified by cold front. Strong vertical wind shear in the lower level was favorable for the formed convective strong storm to maintain and strengthen. The severe hails were produced by isolated supercells and dominant supercells in multicells. In comparison, the isolated supercells were larger and persisted longer. The structures of the supercells reflected typical features such as mesocyclone， high mass center, low-level inflow, weak echo zone and echo drape, middle-level radial convergence and storm-top divergence, etc. The vertically integrated liquid （VIL） and the VIL density maintained high above 35 kg·m-2 and 4 g ·m-3 for a long time in the winter. The hail index of radar algorithm predicts the severe hail with high probability. This process occurred at the end of winter. The typical storm structure showed up after the emergence of convection, and the early warning of hail could be made 10-30 minutes in advance. However, for the short-time potential forecast of severe hail several hours in advance before the occurrence of severe convection, the key parameters (such as CAPE， 0-6 km vertical wind shear and melting layer height) for judging the potential of severe hail are not typical, which will mislead forecasters to ignore the hail potential judgment. Forecasters need to be extremely cautious and do in-depth analysis when conducting potential analysis of severe convective weather in this environmental background, so as to obtain correct forecast results.
2022, 48(5):633-646.
DOI: 10.7519/j.issn.1000-0526.2021.051001
Abstract:
Based on hourly and 5 min observation data of automatic weather station, SWAN mosaic product of radar composite reflectivity in the middle reaches of the Yangtze River and NCEP FNL reanalysis data, the characteristics of four convective storms with low-echo-centroid of short-term heavy precipitation in Wuhan are analyzed. The results show that the characteristics of convective system induced by different weather backgrounds are different. Under the background of baroclinic instability caused by low-level warm forcing, the environmental conditions are high energy and high humidity, and the accumulation of thunderstorm cold pool is conductive to triggering linear severe convection in the stable precipitation front. Under the baroclinic frontogenesis background, the convergence of cold and warm air is intense, strengthening the baroclinicity; there are more mesoscale cyclonic waves on the ground, and the stable precipitation in the front area is often accompanied by a short-time heavy rainfall. Under the quasi barotropic background, the baroclinic atmosphere is weak, but the high-energy and high-humidity environment as well as the near-surface flow field forcing and local thermal difference are easy to trigger severe thermal convection activities. In addition, according to the radar echo characteristics and precipitation characteristics of convective storms, the TS (trailing stratiform cloud) type moves faster, resulting in a small range of short-time heavy rainfall. Quasi-stationary type shows that the echoes of large-scale stratiform cloud with zonal trend are stable, and there are multiple cumulus convective echoes in the middle. The precipitation enhancement in each stage corresponds to the new convective cell passing through Wuhan Station. The consolidation type is in the circulation when the waves merge, often accompanied by the occurrence of heavy rainfall, and the echo shape and direction after merging affect the intensity and duration of precipitation. Actually, under different environmental backgrounds, triggering inducement and organizational form, the surface meteorological elements before and after the occurrence of short-time heavy rainfall show different change characteristics. The different fronts and convection triggering positions lead to different changes in temperature. Ground mesoscale system plays an important role in triggering and organizing the development of mesoscale convective system (MCS). Its generation, elimination and transformation usually have a certain advance in time for MCS. So, paying attention to the development and evolution of ground mesoscale systems such as ground convergence line and temperature front area is of great significance for predicting the triggering and organizational evolution of MCS.
Based on hourly and 5 min observation data of automatic weather station, SWAN mosaic product of radar composite reflectivity in the middle reaches of the Yangtze River and NCEP FNL reanalysis data, the characteristics of four convective storms with low-echo-centroid of short-term heavy precipitation in Wuhan are analyzed. The results show that the characteristics of convective system induced by different weather backgrounds are different. Under the background of baroclinic instability caused by low-level warm forcing, the environmental conditions are high energy and high humidity, and the accumulation of thunderstorm cold pool is conductive to triggering linear severe convection in the stable precipitation front. Under the baroclinic frontogenesis background, the convergence of cold and warm air is intense, strengthening the baroclinicity; there are more mesoscale cyclonic waves on the ground, and the stable precipitation in the front area is often accompanied by a short-time heavy rainfall. Under the quasi barotropic background, the baroclinic atmosphere is weak, but the high-energy and high-humidity environment as well as the near-surface flow field forcing and local thermal difference are easy to trigger severe thermal convection activities. In addition, according to the radar echo characteristics and precipitation characteristics of convective storms, the TS (trailing stratiform cloud) type moves faster, resulting in a small range of short-time heavy rainfall. Quasi-stationary type shows that the echoes of large-scale stratiform cloud with zonal trend are stable, and there are multiple cumulus convective echoes in the middle. The precipitation enhancement in each stage corresponds to the new convective cell passing through Wuhan Station. The consolidation type is in the circulation when the waves merge, often accompanied by the occurrence of heavy rainfall, and the echo shape and direction after merging affect the intensity and duration of precipitation. Actually, under different environmental backgrounds, triggering inducement and organizational form, the surface meteorological elements before and after the occurrence of short-time heavy rainfall show different change characteristics. The different fronts and convection triggering positions lead to different changes in temperature. Ground mesoscale system plays an important role in triggering and organizing the development of mesoscale convective system (MCS). Its generation, elimination and transformation usually have a certain advance in time for MCS. So, paying attention to the development and evolution of ground mesoscale systems such as ground convergence line and temperature front area is of great significance for predicting the triggering and organizational evolution of MCS.
2022, 48(5):647-657.
DOI: 10.7519/j.issn.1000-0526.2021.083102
Abstract:
The differences in haze occurrence frequency identified by two different standards， i.e., the Observation and Forecasting Levels of Haze (QX/T 113-2010) (hereafter referred to as 2010QX) and the Haze Identification for Meteorological Observation (GB/T 36542-2018) (hereafter referred to as 2018GB) are analyzed by employing the hourly meteorological data and particulate matter (PM2.5) mass concentration from March 2016 to February 2020. The results show that the occurrence frequency of haze identified by 2018GB is significantly higher than that of haze identified by 2010QX. However, the numbers of haze days obtained by these two standards are equivalent if we take haze phenomena lasting for 6 h or more as the criterion of haze days. When 80%≤RH<95%, the haze occurrence frequency identified by 2018GB is higher than that of 2010QX. The higher the humidity, the more it increases. Aerosol hygroscopicity parameter has a great influence on the calculation of aerosol extinction coefficient, and the difference of this parameter in different regions should be paid more attention to when using the 2018GB. When PM2.5≤75 μg·m-3, 2018GB can still identify haze, showing the influence of humidity on visibility. The difference of haze occurrence between the two distinguishing methods decreases when the pollution level is moderate-high. The monthly variation of haze occurrence frequency in all cities in Shaanxi Province presents a U-shaped distribution with high in winter and low in summer, and the monthly haze occurrence frequency is highest in January. Except in Yulin and Yan’an in northern Shaanxi and Shangluo in southern Shaanxi, the diurnal variation of hourly haze occurrence frequency shows a single peak in the morning from 09:00 BT to 11:00 BT, while the diurnal variation of hourly haze occurrence frequency in other cities has a bimodal distribution with peaks in the morning from 09:00 BT to 11:00 BT and in the evening from 20:00 BT to 23:00 BT.
The differences in haze occurrence frequency identified by two different standards， i.e., the Observation and Forecasting Levels of Haze (QX/T 113-2010) (hereafter referred to as 2010QX) and the Haze Identification for Meteorological Observation (GB/T 36542-2018) (hereafter referred to as 2018GB) are analyzed by employing the hourly meteorological data and particulate matter (PM2.5) mass concentration from March 2016 to February 2020. The results show that the occurrence frequency of haze identified by 2018GB is significantly higher than that of haze identified by 2010QX. However, the numbers of haze days obtained by these two standards are equivalent if we take haze phenomena lasting for 6 h or more as the criterion of haze days. When 80%≤RH<95%, the haze occurrence frequency identified by 2018GB is higher than that of 2010QX. The higher the humidity, the more it increases. Aerosol hygroscopicity parameter has a great influence on the calculation of aerosol extinction coefficient, and the difference of this parameter in different regions should be paid more attention to when using the 2018GB. When PM2.5≤75 μg·m-3, 2018GB can still identify haze, showing the influence of humidity on visibility. The difference of haze occurrence between the two distinguishing methods decreases when the pollution level is moderate-high. The monthly variation of haze occurrence frequency in all cities in Shaanxi Province presents a U-shaped distribution with high in winter and low in summer, and the monthly haze occurrence frequency is highest in January. Except in Yulin and Yan’an in northern Shaanxi and Shangluo in southern Shaanxi, the diurnal variation of hourly haze occurrence frequency shows a single peak in the morning from 09:00 BT to 11:00 BT, while the diurnal variation of hourly haze occurrence frequency in other cities has a bimodal distribution with peaks in the morning from 09:00 BT to 11:00 BT and in the evening from 20:00 BT to 23:00 BT.
2022, 48(5):658-664.
DOI: 10.7519/j.issn.1000-0526.2022.041302
Abstract:
The main characteristics of the general atmospheric circulation in February 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere, with the subcenter located from the Sea of Okhotsk to the North Pacific Ocean which was stronger compared to the same period in history. The atmospheric circulation in the middle and high latitudes of Eurasia gradually changed from the “two troughs and a ridge” type to the “one trough and one ridge” type. The ridge between Ural Mountains and Bajkal was stable and maintained, and the middle and high latitudes of China were in the frontal zone in front of the ridge, with more active trough and cold air activities. The southern branch trough was more frequent in southern China with intensity close to that in normal years, bringing more rain and snow to the region. In February, cold air was active in China, while there were few strong cold air processes. The monthly mean temperature is -3.2℃, 1.9℃ lower than normal (-1.3℃). The monthly mean precipitation is 25.5 mm, 58% more than normal (16.1 mm). Meanwhile, in mid-to-late February, a persistent low-temperature rainy and snowy weather process occurred in the southern part of China.
The main characteristics of the general atmospheric circulation in February 2022 are as follows. There were two polar vortex centers in the Northern Hemisphere, with the subcenter located from the Sea of Okhotsk to the North Pacific Ocean which was stronger compared to the same period in history. The atmospheric circulation in the middle and high latitudes of Eurasia gradually changed from the “two troughs and a ridge” type to the “one trough and one ridge” type. The ridge between Ural Mountains and Bajkal was stable and maintained, and the middle and high latitudes of China were in the frontal zone in front of the ridge, with more active trough and cold air activities. The southern branch trough was more frequent in southern China with intensity close to that in normal years, bringing more rain and snow to the region. In February, cold air was active in China, while there were few strong cold air processes. The monthly mean temperature is -3.2℃, 1.9℃ lower than normal (-1.3℃). The monthly mean precipitation is 25.5 mm, 58% more than normal (16.1 mm). Meanwhile, in mid-to-late February, a persistent low-temperature rainy and snowy weather process occurred in the southern part of China.
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ISSN:1000-0526 CN:11-2282/P