ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,Issue 12,2024 Table of Contents
2024, 50(12):1417-1428.
DOI: 10.7519/j.issn.1000-0526.2024.080101
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 in the Beijing Region. This study presents the CBLH climatology in Beijing by using high resolution ERA5 reanalysis data during 1992-2022. The ERA5 CBLH is first evaluated against radiosonde-derived CBLH. ERA5 can reproduce the CBLH variation characteristics by sounding reasonably well. Then, the interannual, seasonal and diurnal variations of the CBLHs, as well as the correlation between the CBLH and key meteorological parameters are analyzed. The results show that in the past 30 years, the CBLHs in spring and autumn have decreased at the rate of 61.6 m per decade and 13.1 m per decade, respectively, while that in summer and winter have increased at the rate of 2.9 m per decade and 7.7 m per decade, respectively. The median values of CBLH at noon in spring, summer, autumn, and winter are 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 difference of surface temperature and air temperature （Ts-Ta）, we have 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; and 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 in the Beijing Region. This study presents the CBLH climatology in Beijing by using high resolution ERA5 reanalysis data during 1992-2022. The ERA5 CBLH is first evaluated against radiosonde-derived CBLH. ERA5 can reproduce the CBLH variation characteristics by sounding reasonably well. Then, the interannual, seasonal and diurnal variations of the CBLHs, as well as the correlation between the CBLH and key meteorological parameters are analyzed. The results show that in the past 30 years, the CBLHs in spring and autumn have decreased at the rate of 61.6 m per decade and 13.1 m per decade, respectively, while that in summer and winter have increased at the rate of 2.9 m per decade and 7.7 m per decade, respectively. The median values of CBLH at noon in spring, summer, autumn, and winter are 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 difference of surface temperature and air temperature （Ts-Ta）, we have 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; and when the Ts-Ta increases by 1℃, the CBLH increases by 175 m.
2024, 50(12):1429-1440.
DOI: 10.7519/j.issn.1000-0526.2024.101401
Abstract:
The Huaihe River Basin (HRB), situated in the transitional area between northern and southern climate zones of China, is characterized by a complex geographical environment. Understanding flash droughts in the HRB is crucial for ensuring agricultural production. This study examines the spatial and temporal distribution characteristics and data uncertainty of flash droughts in the HRB from 2000 to 2020 using four sets of soil moisture data: ERA5, ERA5-LAND, GLDAS 2.1 and GLEAM 3.8a. The annual flash drought statistics show that the average occurrence count of flash droughts is generally higher in the ERA5 dataset, with a relatively uniform spatial distribution, while the results of the other three datasets exhibit a spatial distribution pattern of fewer occurrences in the north and more in the south. The average duration of flash droughts exhibits an approximately opposite distribution to their occurrence count distribution. The average occurrence count of flash droughts determines the spatial distribution of the occurrence frequency of flash droughts. Additionally, there is significant interannual variability in the occurrence count of flash droughts with considerable data uncertainty. Flash droughts in the HRB occur frequently during the crop growing seasons (April to September). Focusing on the crop growing seasons, the spatial distribution of the average occurrence count of flash droughts is similar to that of the annual results. However, the average duration of flash droughts tends to be shorter compared to the annual results. The southern region of the HRB experiences more flash droughts during the crop growing seasons, and their interannual trends also exhibit significant data uncertainty.
The Huaihe River Basin (HRB), situated in the transitional area between northern and southern climate zones of China, is characterized by a complex geographical environment. Understanding flash droughts in the HRB is crucial for ensuring agricultural production. This study examines the spatial and temporal distribution characteristics and data uncertainty of flash droughts in the HRB from 2000 to 2020 using four sets of soil moisture data: ERA5, ERA5-LAND, GLDAS 2.1 and GLEAM 3.8a. The annual flash drought statistics show that the average occurrence count of flash droughts is generally higher in the ERA5 dataset, with a relatively uniform spatial distribution, while the results of the other three datasets exhibit a spatial distribution pattern of fewer occurrences in the north and more in the south. The average duration of flash droughts exhibits an approximately opposite distribution to their occurrence count distribution. The average occurrence count of flash droughts determines the spatial distribution of the occurrence frequency of flash droughts. Additionally, there is significant interannual variability in the occurrence count of flash droughts with considerable data uncertainty. Flash droughts in the HRB occur frequently during the crop growing seasons (April to September). Focusing on the crop growing seasons, the spatial distribution of the average occurrence count of flash droughts is similar to that of the annual results. However, the average duration of flash droughts tends to be shorter compared to the annual results. The southern region of the HRB experiences more flash droughts during the crop growing seasons, and their interannual trends also exhibit significant data uncertainty.
2024, 50(12):1441-1450.
DOI: 10.7519/j.issn.1000-0526.2024.092301
Abstract:
In June 2024, rainfall in eastern China exhibited a distinct spatial distribution characterized by “droughts in northern China and floods in southern China”. Notably, the rainfall in the area south of Yangtze River exceeded the historic record since 1961. Both the results of the statistical analysis and the case study have demonstrated that the anomalous southerly moisture transport on the western side of the Western Pacific subtropical high (WPSH) played a significant function. However, the general circulation to the west of 110°E showed different characteristics from those in historical events. The eastern boundary of the North Africa high (NAH) exhibited a notable eastward and southward extension, connecting the western boundary of the WPSH over the southern tropical Indian Ocean. This resulted in the formation of an “inverted Ω” circulation pattern, a phenomenon that has never been observed previously. In addition to the El Nino, the record-breaking warm sea surface temperature (SST) in the western tropical Indian Ocean was another significant impact factor for the abnormal rainfall in the area south of the Yangtze River in early summer. From January to February 2024, the SST anomaly over the west part (20°S-20°N, 40°-75°E) of tropical Indian Ocean, exceeded 1℃ for the first time. The thermal effect of the underlying surface caused the rise in air temperature below 600 hPa over the domain. The thermal expansion of the air column led to an increase in geopotential height over the eastern boundary of the NAH, which in turn contributed to an intensification of the north wind component. It can be concluded that the formation of the “inverted Ω” circulation pattern was a result of the eastward extension of the NAH and westward extension of the WPSH, respectively. This resulted in the development of a strong cyclonic anomaly circulation over the equatorial Indian Ocean. The anomalous southerly wind compoments on its eastern side converged enhancing the transport of southwest moisture flow from the Bay of Bengal to the area south of Yangtze River, resulting in abnormal rainfall in the latter. Statistical analysis from historical observations have also verified this conclusion.
In June 2024, rainfall in eastern China exhibited a distinct spatial distribution characterized by “droughts in northern China and floods in southern China”. Notably, the rainfall in the area south of Yangtze River exceeded the historic record since 1961. Both the results of the statistical analysis and the case study have demonstrated that the anomalous southerly moisture transport on the western side of the Western Pacific subtropical high (WPSH) played a significant function. However, the general circulation to the west of 110°E showed different characteristics from those in historical events. The eastern boundary of the North Africa high (NAH) exhibited a notable eastward and southward extension, connecting the western boundary of the WPSH over the southern tropical Indian Ocean. This resulted in the formation of an “inverted Ω” circulation pattern, a phenomenon that has never been observed previously. In addition to the El Nino, the record-breaking warm sea surface temperature (SST) in the western tropical Indian Ocean was another significant impact factor for the abnormal rainfall in the area south of the Yangtze River in early summer. From January to February 2024, the SST anomaly over the west part (20°S-20°N, 40°-75°E) of tropical Indian Ocean, exceeded 1℃ for the first time. The thermal effect of the underlying surface caused the rise in air temperature below 600 hPa over the domain. The thermal expansion of the air column led to an increase in geopotential height over the eastern boundary of the NAH, which in turn contributed to an intensification of the north wind component. It can be concluded that the formation of the “inverted Ω” circulation pattern was a result of the eastward extension of the NAH and westward extension of the WPSH, respectively. This resulted in the development of a strong cyclonic anomaly circulation over the equatorial Indian Ocean. The anomalous southerly wind compoments on its eastern side converged enhancing the transport of southwest moisture flow from the Bay of Bengal to the area south of Yangtze River, resulting in abnormal rainfall in the latter. Statistical analysis from historical observations have also verified this conclusion.
2024, 50(12):1451-1466.
DOI: 10.7519/j.issn.1000-0526.2024.061401
Abstract:
To study the mesoscale characteristics and causes of extreme short-time severe precipitation at night in Tianjin，by using automatic weather station data, minutely precipitation data, Doppler weather radar data, wind profile data and ERA5 reanalysis data, this paper analyzes the extreme short-time severe precipitation that occurred in Tianjin in the early morning of 3 July 2022. The results show that there was no significant low-value weather system at 500 hPa and no synoptic-scale low-level jet background at the lower level when this severe precipitation occurred. It was a rainstorm process mainly caused by small-scale and meso scale systems forcing under a typical circulation situation, having obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused the precipitation was present in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echoes. Its radar echo had a high centroid, showing the characteristics of continental severe convective echoes. With high temperature and humidity, the enhancement of the 975 hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the surface, and the mid-level dry cold air intrusion enhanced instability triggering the initial convection. The cold pool formed by the initial convection made up of 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 meso-γ scale 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 developed inversion stratification made the warm and moist air from the southeast sea continuously strengthen into the boundary layer jet, causing the vertical wind shear of 0.1-2.5 km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhancing cold pool reached a temporary equilibrium. Thus, the vortex in front of the outflow boundary continued to strengthen and developed from the bottom to top. The strong dynamic convergence accompanying the vortex directly led to the rapid growth of minute-level rain intensity lasting for several minutes, which finally resulted in the emergence of extreme short-time severe precipitation. The results could provide a reference basis for predicting local short-time severe precipitation at night and exploring its occurrence and development mechanisms in North China.
To study the mesoscale characteristics and causes of extreme short-time severe precipitation at night in Tianjin，by using automatic weather station data, minutely precipitation data, Doppler weather radar data, wind profile data and ERA5 reanalysis data, this paper analyzes the extreme short-time severe precipitation that occurred in Tianjin in the early morning of 3 July 2022. The results show that there was no significant low-value weather system at 500 hPa and no synoptic-scale low-level jet background at the lower level when this severe precipitation occurred. It was a rainstorm process mainly caused by small-scale and meso scale systems forcing under a typical circulation situation, having obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused the precipitation was present in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echoes. Its radar echo had a high centroid, showing the characteristics of continental severe convective echoes. With high temperature and humidity, the enhancement of the 975 hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the surface, and the mid-level dry cold air intrusion enhanced instability triggering the initial convection. The cold pool formed by the initial convection made up of 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 meso-γ scale 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 developed inversion stratification made the warm and moist air from the southeast sea continuously strengthen into the boundary layer jet, causing the vertical wind shear of 0.1-2.5 km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhancing cold pool reached a temporary equilibrium. Thus, the vortex in front of the outflow boundary continued to strengthen and developed from the bottom to top. The strong dynamic convergence accompanying the vortex directly led to the rapid growth of minute-level rain intensity lasting for several minutes, which finally resulted in the emergence of extreme short-time severe precipitation. The results could provide a reference basis for predicting local short-time severe precipitation at night and exploring its occurrence and development mechanisms in North China.
5 Analysis of Multi-Source Observation of the Disastrous Tornado in Funing County on 19 September 2023
2024, 50(12):1467-1479.
DOI: 10.7519/j.issn.1000-0526.2024.070101
Abstract:
One mixed severe convection process which was accompanied by tornadoes, occurred in Huang-Huai Region (Yellow River and Huaihe River) and Jiang-Huai Region (Yangtze River and Huaihe River) from north to south on 19 September 2023. Funing strong tornado (corresponding to EF3) was the strongest tornado, which was 1.2 km away from Tongying Village where extremely strong wind of 41.8 m·s-1 (Scale 14) was observed. Based on the data from ground automatic weather stations and sounding stations, data from S-band dual-polarization radar, we analyze the Funing strong tornado in this paper. The results show that the tornado occurred in the strong warm and moist zone between the subtropical anticyclone and the low-level shear line. The slope of low-level front was large. The convergence line moved southward on the ground rapidly, combined with extremely low height of lifting condensation, low convective inhibition, high convective available potential energy and vertical wind shear. These conditions were favorable for the formation of tornadoes. The Funing strong tornado was a typical severe rainfall supercell tornado, characterized by hook echo, bounded weak echo region and deep strong meso-cyclone. The high, slanting, strong echo extended to the height over 16 km. Tornado debris signature (TDS) observed by dual-polarization radar was wide, indicating the tornado was strong and destructive. Affected by strong vertical wind shear, the differential reflectivity (ZDR) arcs separated from the strong specific differential phase (KDP) center in the hook echo, and the inclined vertical circulation was conducive to the maintenance and development of the storm. Heavy precipitation echo with low centroid appeared in the front of TDS. After rainfall and temperature cooling appeared on the ground, ZDR arcs and ZDR columns weakened and disappeared, and then the tornado weakened rapidly.
One mixed severe convection process which was accompanied by tornadoes, occurred in Huang-Huai Region (Yellow River and Huaihe River) and Jiang-Huai Region (Yangtze River and Huaihe River) from north to south on 19 September 2023. Funing strong tornado (corresponding to EF3) was the strongest tornado, which was 1.2 km away from Tongying Village where extremely strong wind of 41.8 m·s-1 (Scale 14) was observed. Based on the data from ground automatic weather stations and sounding stations, data from S-band dual-polarization radar, we analyze the Funing strong tornado in this paper. The results show that the tornado occurred in the strong warm and moist zone between the subtropical anticyclone and the low-level shear line. The slope of low-level front was large. The convergence line moved southward on the ground rapidly, combined with extremely low height of lifting condensation, low convective inhibition, high convective available potential energy and vertical wind shear. These conditions were favorable for the formation of tornadoes. The Funing strong tornado was a typical severe rainfall supercell tornado, characterized by hook echo, bounded weak echo region and deep strong meso-cyclone. The high, slanting, strong echo extended to the height over 16 km. Tornado debris signature (TDS) observed by dual-polarization radar was wide, indicating the tornado was strong and destructive. Affected by strong vertical wind shear, the differential reflectivity (ZDR) arcs separated from the strong specific differential phase (KDP) center in the hook echo, and the inclined vertical circulation was conducive to the maintenance and development of the storm. Heavy precipitation echo with low centroid appeared in the front of TDS. After rainfall and temperature cooling appeared on the ground, ZDR arcs and ZDR columns weakened and disappeared, and then the tornado weakened rapidly.
2024, 50(12):1480-1494.
DOI: 10.7519/j.issn.1000-0526.2024.080502
Abstract:
A squall line occurred in Sichuan Basin on 11 April 2022, causing extreme thunderstorm gale (37.4 m·s-1). Due to the poor understanding of the rapid development mechanism of the squall line, there were large deviations in the forecast of short-time severe rainfall and gale during the squall line process. Based on multi-source observation data and ERA5 reanalysis data, the circulation background and echo evolution as well as the maintenance and extinction of the squall line are analyzed. The results are as follows. The squall line occurred in the mutual coupling area of upper trough at 500 hPa and the southerly jet at 700 hPa. Upper-level divergence and low-level convergence were significantly enhanced before the squall line formed, which provided dynamic conditions for the development of the storm. In the south-central part of Sichuan Basin, the convective available potential energy (CAPE) was greater than 1000 J·kg-1, the deep and shallow vertical wind shears were greater than 15 m·s-1, the height of wet bulb temperature 0℃ was 3.8 km， the height of -20℃ was 7 km, the vertical temperature lapse rate was 6.88℃·km-1 and a “bell mouth” existed in temperature humidity profile below lifting condensation level. Especially, the vertical wind shear, mid-level dry layer and downdraft CAPE approached or exceeded the extreme values, which provided favorable environmental conditions for the merging and development of the squall line and the occurrence of severe thunderstorms and gale. Convections in the northern segment of the squall line were triggered, developing under the combination influence of the terrain of Longquan Mountains, cold pool and surface convergence line. In the south section, convections were uplifted by the dynamic action of the lower level. Due to the 700 hPa jet stream, surface cold pool and convergence line, two sections of linear convection were intensified and merged into a north-south squall line system with super-cell storms and bow echoes when moving eastward to the high energy and humidity areas in central basin. Super-cells before the formation of squall line and the echoes of the mature squall line both had overhang echoes, weak echo zones, rear inflow and mid-level radial convergence. Downdraft formed by the rear inflow and dry curl in the middle troposphere made the supercell storm and cold pool move faster than other parts. Then, a bow echo was formed. Because of the gale of downburst and precipitation, propagation velocity of the cold pool was significantly stronger than the 0－3 km vertical wind shear, which was an important cause for the rapid extinction the squall line.
A squall line occurred in Sichuan Basin on 11 April 2022, causing extreme thunderstorm gale (37.4 m·s-1). Due to the poor understanding of the rapid development mechanism of the squall line, there were large deviations in the forecast of short-time severe rainfall and gale during the squall line process. Based on multi-source observation data and ERA5 reanalysis data, the circulation background and echo evolution as well as the maintenance and extinction of the squall line are analyzed. The results are as follows. The squall line occurred in the mutual coupling area of upper trough at 500 hPa and the southerly jet at 700 hPa. Upper-level divergence and low-level convergence were significantly enhanced before the squall line formed, which provided dynamic conditions for the development of the storm. In the south-central part of Sichuan Basin, the convective available potential energy (CAPE) was greater than 1000 J·kg-1, the deep and shallow vertical wind shears were greater than 15 m·s-1, the height of wet bulb temperature 0℃ was 3.8 km， the height of -20℃ was 7 km, the vertical temperature lapse rate was 6.88℃·km-1 and a “bell mouth” existed in temperature humidity profile below lifting condensation level. Especially, the vertical wind shear, mid-level dry layer and downdraft CAPE approached or exceeded the extreme values, which provided favorable environmental conditions for the merging and development of the squall line and the occurrence of severe thunderstorms and gale. Convections in the northern segment of the squall line were triggered, developing under the combination influence of the terrain of Longquan Mountains, cold pool and surface convergence line. In the south section, convections were uplifted by the dynamic action of the lower level. Due to the 700 hPa jet stream, surface cold pool and convergence line, two sections of linear convection were intensified and merged into a north-south squall line system with super-cell storms and bow echoes when moving eastward to the high energy and humidity areas in central basin. Super-cells before the formation of squall line and the echoes of the mature squall line both had overhang echoes, weak echo zones, rear inflow and mid-level radial convergence. Downdraft formed by the rear inflow and dry curl in the middle troposphere made the supercell storm and cold pool move faster than other parts. Then, a bow echo was formed. Because of the gale of downburst and precipitation, propagation velocity of the cold pool was significantly stronger than the 0－3 km vertical wind shear, which was an important cause for the rapid extinction the squall line.
2024, 50(12):1495-1508.
DOI: 10.7519/j.issn.1000-0526.2024.101501
Abstract:
The spatio-temporal distribution of thunderstorm gales (TGs) in Jiangxi is comprehensively analyzed based on hourly observation data of automatic weather stations, cloud-to-ground lightning observations and weather radar data in Jiangxi Province from 2015 to 2023. The ERA5 reanalysis data are further used to investigate the atmospheric environment before the onset of TGs. The results show that the TGs in Jiangxi occur mainly in spring and summer, with significant seasonal variations and differences in the north-central part and the south. The frequency of TGs occurring in spring is only slightly higher than in summer in north-central Jiangxi, but the frequency of TGs in summer is more than twice of that in spring in the south of Jiangxi. TGs have obvious diurnal variation with the highest occurrence frequency from 14:00 BT to 20:00 BT. The frequency of TGs from evening into night in north-central Jiangxi is much higher than in the southern part. The thermodynamic, dynamic and water vapor characteristics of TGs are significantly different in spatio-temporal distributions. In the same season, the dynamic effect is generally stronger in north-central Jiangxi than in the southern part, while the thermodynamic and water vapor effects are stronger in the south than in north-central part. The thermodynamic and water vapor effects are stronger in summer than in spring, but the dynamic effect in spring is stronger. The convective instability energy required for TGs varies by time periods, but all occur under unstable conditions. TGs occur more frequently under low vertical wind shear in the afternoon and also in the deep night with strong vertical wind shear conditions. Besides, the upper-level dry and low-level wet structure in the daytime is more pronounced than at night. Therefore, it is crucial to set ambient parameter thresholds by season, region and time period, in order to provide more accurate guidance on TGs forecast and warning. When 0-6 km vertical wind shear (Shear6) is large enough and distributed in the range of 30-33 m·s-1 in spring in north-central Jiangxi, it is imperative to be alert to the advent of TGs even if most unstable convective available potential energy (MUCAPE) is only in the range of 0-500 J·kg-1 and precipitable water (PW) only in the range of 43-48 mm. To accurately forecast the occurrence of TGs in summer, it is essential to pay attention to the MUCAPE and PW, and especially in the south of Jiangxi, TGs tend to occur with higher frequency under weak mid-level vertical wind shear. When PW>60 mm and MUCAPE>1500 J·kg-1, even though Shear6 is minimal and confined to a range of 5-8 m·s-1, it is necessary to contemplate the potential for TGs. The increase of water vapor is important for the occurrence of TGs in different regions during different seasons. Therefore, changes in PW should be focused on in the operation of forecasting TGs.
The spatio-temporal distribution of thunderstorm gales (TGs) in Jiangxi is comprehensively analyzed based on hourly observation data of automatic weather stations, cloud-to-ground lightning observations and weather radar data in Jiangxi Province from 2015 to 2023. The ERA5 reanalysis data are further used to investigate the atmospheric environment before the onset of TGs. The results show that the TGs in Jiangxi occur mainly in spring and summer, with significant seasonal variations and differences in the north-central part and the south. The frequency of TGs occurring in spring is only slightly higher than in summer in north-central Jiangxi, but the frequency of TGs in summer is more than twice of that in spring in the south of Jiangxi. TGs have obvious diurnal variation with the highest occurrence frequency from 14:00 BT to 20:00 BT. The frequency of TGs from evening into night in north-central Jiangxi is much higher than in the southern part. The thermodynamic, dynamic and water vapor characteristics of TGs are significantly different in spatio-temporal distributions. In the same season, the dynamic effect is generally stronger in north-central Jiangxi than in the southern part, while the thermodynamic and water vapor effects are stronger in the south than in north-central part. The thermodynamic and water vapor effects are stronger in summer than in spring, but the dynamic effect in spring is stronger. The convective instability energy required for TGs varies by time periods, but all occur under unstable conditions. TGs occur more frequently under low vertical wind shear in the afternoon and also in the deep night with strong vertical wind shear conditions. Besides, the upper-level dry and low-level wet structure in the daytime is more pronounced than at night. Therefore, it is crucial to set ambient parameter thresholds by season, region and time period, in order to provide more accurate guidance on TGs forecast and warning. When 0-6 km vertical wind shear (Shear6) is large enough and distributed in the range of 30-33 m·s-1 in spring in north-central Jiangxi, it is imperative to be alert to the advent of TGs even if most unstable convective available potential energy (MUCAPE) is only in the range of 0-500 J·kg-1 and precipitable water (PW) only in the range of 43-48 mm. To accurately forecast the occurrence of TGs in summer, it is essential to pay attention to the MUCAPE and PW, and especially in the south of Jiangxi, TGs tend to occur with higher frequency under weak mid-level vertical wind shear. When PW>60 mm and MUCAPE>1500 J·kg-1, even though Shear6 is minimal and confined to a range of 5-8 m·s-1, it is necessary to contemplate the potential for TGs. The increase of water vapor is important for the occurrence of TGs in different regions during different seasons. Therefore, changes in PW should be focused on in the operation of forecasting TGs.
2024, 50(12):1509-1518.
DOI: 10.7519/j.issn.1000-0526.2024.080401
Abstract:
Based on the observation data of island stations, buoy sites and coastal stations in Shanghai during 2016-2020, sea fog events at six stations are identified and classified. On this basis, the spatio-temporal characteristics of sea fog events and the changes in space, season, duration, intensity, start and dissipation times of different types of sea fog are analyzed. The results show that there are generally 20-30 sea fog events in different regions throughout the whole year, but they have significant differences in time and space. Radiation fog is the most common type of sea fog, followed by precipitation fog. Advection fog occurs more frequently at Yangshan and offshore sea areas. The seasonal variation of different types of fog varies greatly in different sea areas. In the Yangtze River Estuary sea area, radiation fog and precipitation fog occur every month, with radiation fog being the main type. Advection fog mainly occurs in winter and spring, but its frequency is relatively low. The Jinshan and Yangshan sea areas are dominated by radiation fog every month, with precipitation fog and advection fog mainly seen in spring, summer and winter. The duration of advection fog is generally longer, while the durations of precipitation fog and radiation fog are shorter. The lowest atmospheric visibility value in precipitation fog events is generally higher than that in radiation fog and advection fog, and advection fog often produces the most of severe fog events. Precipitation fog can occur at all the time of the day, while radiation fog and advection fog mainly appear at night. The dissipations of radiation fog and advection fog mainly occur in 1-5 hours after sunrise, and the dissipation time of precipitation fog is more dispersed.
Based on the observation data of island stations, buoy sites and coastal stations in Shanghai during 2016-2020, sea fog events at six stations are identified and classified. On this basis, the spatio-temporal characteristics of sea fog events and the changes in space, season, duration, intensity, start and dissipation times of different types of sea fog are analyzed. The results show that there are generally 20-30 sea fog events in different regions throughout the whole year, but they have significant differences in time and space. Radiation fog is the most common type of sea fog, followed by precipitation fog. Advection fog occurs more frequently at Yangshan and offshore sea areas. The seasonal variation of different types of fog varies greatly in different sea areas. In the Yangtze River Estuary sea area, radiation fog and precipitation fog occur every month, with radiation fog being the main type. Advection fog mainly occurs in winter and spring, but its frequency is relatively low. The Jinshan and Yangshan sea areas are dominated by radiation fog every month, with precipitation fog and advection fog mainly seen in spring, summer and winter. The duration of advection fog is generally longer, while the durations of precipitation fog and radiation fog are shorter. The lowest atmospheric visibility value in precipitation fog events is generally higher than that in radiation fog and advection fog, and advection fog often produces the most of severe fog events. Precipitation fog can occur at all the time of the day, while radiation fog and advection fog mainly appear at night. The dissipations of radiation fog and advection fog mainly occur in 1-5 hours after sunrise, and the dissipation time of precipitation fog is more dispersed.
2024, 50(12):1519-1530.
DOI: 10.7519/j.issn.1000-0526.2024.052801
Abstract:
In order to enhance the prediction accuracy of 0-2 h nowcasting of short-time heavy precipitation and thunderstorm gale, this paper proposes a severe convection probability nowcasting 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. 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 rainy season (June-September 2023) in Zhejiang show that the CSCPVP method has significantly improved the nowcasting ability of two types of severe convection than the existing operational methods. Overall, the new method has improved 0-2 h nowcasting ability of systematic, local and distributed severe convection. The critical success index of short-time heavy precipitation increases from 8%-16% to 22%-26%, and the critical success index of thunderstorm gale increases from 7% to 10%-11%. Thus, the problem of false alarms and missing prediction has been effectively improved.
In order to enhance the prediction accuracy of 0-2 h nowcasting of short-time heavy precipitation and thunderstorm gale, this paper proposes a severe convection probability nowcasting 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. 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 rainy season (June-September 2023) in Zhejiang show that the CSCPVP method has significantly improved the nowcasting ability of two types of severe convection than the existing operational methods. Overall, the new method has improved 0-2 h nowcasting ability of systematic, local and distributed severe convection. The critical success index of short-time heavy precipitation increases from 8%-16% to 22%-26%, and the critical success index of thunderstorm gale increases from 7% to 10%-11%. Thus, the problem of false alarms and missing prediction has been effectively improved.
2024, 50(12):1531-1541.
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 difficulty in current typhoon forecasting. Based on the XGBoost model, this article uses the NCEP GFS analysis and forecast data in 2015-2020, and IBTrACS data to construct RI forecast model (FM) and forecast correction model (FCM) for typhoons in the Northwest Pacific 24 h in advance. Through predictor contribution analysis of the FM, we have found that the five factors that have the greatest impact on model forecasts are typhoon abundance, average temperature at 200 hPa, intensity changes over the past 6 h, potential intensity, and average divergence at 200 hPa. The model is independently tested with the data in 2021-2022, and the results show that the FM has higher accuracy when tested by analytical data, with false negative rate (FNR), false positive rate (FPR) and threat score (TS) being 0.25, 0.24 and 0.32, respectively. However, due to the influence of forecast errors caused by forecast factors, the performance of FM in real-time forecasting decreases (FNR, FPR and TS are 0.32, 0.26 and 0.27, respectively). The FCM constructed based on forecast data can effectively correct the forecast errors by learning them, thereby reducing the impact of forecast errors. The FNR, FPR and TS of the FCM in real-time forecasting tests are 0.28, 0.25 and 0.30, respectively; compared with the FM, the FNR and FPR are reduced by 0.04 and 0.01, but the TS rises by 0.03. Thus, the FCM is convenient and easy to use, and can provide 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 difficulty in current typhoon forecasting. Based on the XGBoost model, this article uses the NCEP GFS analysis and forecast data in 2015-2020, and IBTrACS data to construct RI forecast model (FM) and forecast correction model (FCM) for typhoons in the Northwest Pacific 24 h in advance. Through predictor contribution analysis of the FM, we have found that the five factors that have the greatest impact on model forecasts are typhoon abundance, average temperature at 200 hPa, intensity changes over the past 6 h, potential intensity, and average divergence at 200 hPa. The model is independently tested with the data in 2021-2022, and the results show that the FM has higher accuracy when tested by analytical data, with false negative rate (FNR), false positive rate (FPR) and threat score (TS) being 0.25, 0.24 and 0.32, respectively. However, due to the influence of forecast errors caused by forecast factors, the performance of FM in real-time forecasting decreases (FNR, FPR and TS are 0.32, 0.26 and 0.27, respectively). The FCM constructed based on forecast data can effectively correct the forecast errors by learning them, thereby reducing the impact of forecast errors. The FNR, FPR and TS of the FCM in real-time forecasting tests are 0.28, 0.25 and 0.30, respectively; compared with the FM, the FNR and FPR are reduced by 0.04 and 0.01, but the TS rises by 0.03. Thus, the FCM is convenient and easy to use, and can provide reference for real-time forecasting of typhoon intensity and typhoon RI.
2024, 50(12):1542-1550.
DOI: 10.7519/j.issn.1000-0526.2024.061701
Abstract:
In this study, a random-forest-based model of atmospheric CO2 column concentration over the South China Sea was built with the data of 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 satellite remote sensing data. The accuracy of the model was verified by the data in 2020, with Bias being 0.27 ppm, R2 being 0.59 and RMSE being 1.00 ppm. The results show that the atmospheric CO2 column concentration in the South China Sea pre-sents obvious seasonal characteristics, with the highest value in spring, followed by that in summer, winter and autumn in sequence. Moreover, the main impact factors for the seasonal differences of atmospheric CO2 column concentration in the South China Sea vary with time. In January and April, it is affected mainly by wind direction. In July, wind speed and wind direction are the two major impact factors. In October, sea surface temperature is the major factor. This method established based on the multisource satellite remote sensing data can realize the high-frequency and full-coverage monitoring of atmospheric CO2 column concentration in the South China Sea.
In this study, a random-forest-based model of atmospheric CO2 column concentration over the South China Sea was built with the data of 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 satellite remote sensing data. The accuracy of the model was verified by the data in 2020, with Bias being 0.27 ppm, R2 being 0.59 and RMSE being 1.00 ppm. The results show that the atmospheric CO2 column concentration in the South China Sea pre-sents obvious seasonal characteristics, with the highest value in spring, followed by that in summer, winter and autumn in sequence. Moreover, the main impact factors for the seasonal differences of atmospheric CO2 column concentration in the South China Sea vary with time. In January and April, it is affected mainly by wind direction. In July, wind speed and wind direction are the two major impact factors. In October, sea surface temperature is the major factor. This method established based on the multisource satellite remote sensing data can realize the high-frequency and full-coverage monitoring of atmospheric CO2 column concentration in the South China Sea.
2024, 50(12):1551-1560.
DOI: 10.7519/j.issn.1000-0526.2024.110801
Abstract:
In September 2024, the western Pacific subtropical high was significantly more westward and stronger than usual, controlling most regions of southern of China. The persistent high temperature and less rainfall in Sichuan, Chongqing and the middle reaches of the Yangtze River regions led to the continuous worsening of meteorological drought. In northern of China, zonal westerly circulation played the main theme, so there was not much active cold air. In September, the national mean temperature was 18.5℃, 1.6℃ higher than that of the same period of normal years, with high temperature weather mainly experienced in the area south of Yangtze River, the South China and the eastern part of Southwest China. The national average precipitation was 78.7 mm, 20.5% more 〖JP2〗than the normal value. 〖JP〗The autumn rain of West China began on 29 September, which was 27 days 〖JP2〗later than the usual onset date (2 September) and recorded〖JP〗 the latest since 1961. Areas with excessive rainfall were mainly impacted by typhoons. There were eight typhoons generated in the Northwest Pacific and the South China Sea, three typhoons more than the five in the same period of normal years. Among them, three typhoons made landfall, 1.3 more than normal (1.7). The Super Typhoon Yagi was the strongest typhoon making landfall in China in autumn since 1949. Under Yagi’s influence, severe torrential rain occurred in Hainan, Guangxi and other regions. On 16 and 19 September, the two typhoons Bebinca and Pulasan landed in Shanghai consecutively, and the time interval between them was the shortest in Shanghai as recorded. As a result, parts of East China received heavy rain or torrential rain, and some localized regions even experienced torrential rain or severe torrential rain.
In September 2024, the western Pacific subtropical high was significantly more westward and stronger than usual, controlling most regions of southern of China. The persistent high temperature and less rainfall in Sichuan, Chongqing and the middle reaches of the Yangtze River regions led to the continuous worsening of meteorological drought. In northern of China, zonal westerly circulation played the main theme, so there was not much active cold air. In September, the national mean temperature was 18.5℃, 1.6℃ higher than that of the same period of normal years, with high temperature weather mainly experienced in the area south of Yangtze River, the South China and the eastern part of Southwest China. The national average precipitation was 78.7 mm, 20.5% more 〖JP2〗than the normal value. 〖JP〗The autumn rain of West China began on 29 September, which was 27 days 〖JP2〗later than the usual onset date (2 September) and recorded〖JP〗 the latest since 1961. Areas with excessive rainfall were mainly impacted by typhoons. There were eight typhoons generated in the Northwest Pacific and the South China Sea, three typhoons more than the five in the same period of normal years. Among them, three typhoons made landfall, 1.3 more than normal (1.7). The Super Typhoon Yagi was the strongest typhoon making landfall in China in autumn since 1949. Under Yagi’s influence, severe torrential rain occurred in Hainan, Guangxi and other regions. On 16 and 19 September, the two typhoons Bebinca and Pulasan landed in Shanghai consecutively, and the time interval between them was the shortest in Shanghai as recorded. As a result, parts of East China received heavy rain or torrential rain, and some localized regions even experienced torrential rain or severe torrential rain.
Mobile website
® 2025 All Rights Reserved
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
ISSN:1000-0526 CN:11-2282/P