Based on the 4 times daily 0.75°×0.75°ERA-Interim data,the relationship between precipitation and a transverse shear line(TSL)over Qinghai-Tibet Plateau during August 15-19,2015 is analyzed.The results ...Based on the 4 times daily 0.75°×0.75°ERA-Interim data,the relationship between precipitation and a transverse shear line(TSL)over Qinghai-Tibet Plateau during August 15-19,2015 is analyzed.The results show that precipitation and TSL had obvious diurnal variation.That is,the intensity of the TSL and the precipitation tended to increase from afternoon to night and reduce from 00:00 to 06:00 UTC(the same below).The shape of the rain area was basically consistent with the direction of the TSL,and when the zonal characteristics of the rain area were obvious,the precipitation distribution was relatively uniform,otherwise the local short-term heavy precipitation was easy to occur.The precipitation center was basically consistent with the positive vorticity center near the TSL,and precipitation was directly proportional to the value of positive vorticity.The equation for the budget of vorticity shows that the horizontal advection term determined the moving direction of the TSL.The vertical transportation term determined the structural characteristics of the TSL on the vertical section,and positive vertical transport item of lower level was conducive to the formation of the plateau vortex.The horizontal convergence or divergence term determined the position of the TSL,and was conducive to the maintenance of the TSL.The evolution of apparent heat source and apparent water vapor sink near the TSL had a distinct diurnal feature.Meanwhile,atmospheric heating in the precipitation process was closely related to atmospheric upward movement,and the latent heat of condensation release caused by precipitation was beneficial to the maintenance of the plateau shear line and the formation and strengthening of plateau vortex.The precipitation of the TSL was mainly dominated by weak convective precipitation.展开更多
A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China,leading to heavy precipitation.We examined the differences in the mesoscale characteristics and microphysics...A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China,leading to heavy precipitation.We examined the differences in the mesoscale characteristics and microphysics of the frontal and warm sector rain belts that occurred in South China on May 10–13,2022.The southern rain belt occurred in an environment with favorable mesoscale conditions but weak large-scale forcing.In contrast,the northern rain belt was related to low-level horizontal shear and the surface-level front.The interaction between the enhanced southeasterly winds and the rainfall-induced cold pool promoted the persistent growth of convection along the southern rain belt.The convective cell propagated east over the coastal area,where there was a large temperature gradient.The bow-shaped echo in this region may be closely related to the rear-inflow jet.By contrast,the initial convection of the northern rain belt was triggered along the front and the region of low-level horizontal shear,with mesoscale interactions between the enhanced warm-moist southeasterly airflow and the cold dome associated with the earlier rain.The terrain blocked the movement of the cold pool,resulting in the stagnation of the frontal convective cell at an early stage.Subsequently,a meso-γ-scale vortex formed during the rapid movement of the convective cell,corresponding to an enhancement of precipitation.The representative raindrop spectra for the southern rain belt were characterized by a greater number and higher density of raindrops than the northern rain belt,even though both resulted in comparable hourly rainfalls.These results help us better understand the characteristics of double rain belts over South China.展开更多
Based on the 4 times daily 0.75°× 0.75° ERA-Interim data, the structural evolution of a Qinghai-Tibetan Plateau horizontal (east-west-oriented) shear line (TSL) during 15-19 August 2015 and the effe...Based on the 4 times daily 0.75°× 0.75° ERA-Interim data, the structural evolution of a Qinghai-Tibetan Plateau horizontal (east-west-oriented) shear line (TSL) during 15-19 August 2015 and the effect of diabatic heating on its evolution were analyzed. The results show that the TSL possessed a vertical thickness of up to 1.5 km (approxim-ately 600-450 hPa), and was baroclinic in nature. Weak ascending motions occurred near the TSL, accompanied with more significant gradients in dew point temperature than in temperature. The TSL was characterized by diurnal vari- ations in its appearance and structure. It was relatively full in shape (broken) and was the lowest (highest) in vertical extent at 0000 (1800) UTC, and veered clockwise (anticlockwise) dttring 0000--0600 (1200-1800) UTC. When the north-south span of the TSL increased, it was prone to fracturing; and it disappeared when the dew point temperat-ure gradients to its either side decreased. When the TSL moved northward (southward), its western (eastern) section broke up, while the eastern (western) section inclined to regenerate or merge. The TSL tended to move towards the positive vorticity areas with significant increases in vorticity. When the positive vorticity center moved down, the height of TSL decreased. Further analysis shows that the plateau surface heating dominated the vorticity attribute of the TSL and its movement, with different contributions from local variation, horizontal advection, and vertical advec-tion of the diabatic heating to the TSL at different heights.展开更多
The impacts of different moisture profiles on the structure and vertical motion of squall lines were investigated by conducting a set of numerical simulations.The base state was determined by an observational sounding...The impacts of different moisture profiles on the structure and vertical motion of squall lines were investigated by conducting a set of numerical simulations.The base state was determined by an observational sounding,with high precipitable water representing moist environmental conditions in the East Asian monsoon region.To reveal the impact of moisture at different levels,the moisture content at the middle and low levels were changed in the numerical simulations.The numerical results showed that more convective cells developed and covered a larger area in the high moisture experiments,which was characteristic of the convection during the Meiyu season in China.In addition,high moisture content at low levels favored the development of updrafts and triggered convection of greater intensity.This was demonstrated by the thermodynamic parameters,including Convective Available Potential Energy(CAPE),Lifted Index(LI),Lift Condensation Level(LCL),and Level of Free Convection(LFC).Dry air at middle levels led to strong downdrafts in the environment and updrafts in clouds.This could be because dry air at middle levels favors the release of latent heat,thereby promoting updrafts in clouds and downdrafts in the environment.Therefore,high relative humidity(RH)at low levels and low RH at middle levels favors updrafts in the cloud cores.Additionally,moist air at low levels and dry air at middle levels promotes the development of convective cells and the intensification of cold pool.The squall line can be organized by the outflow boundary induced by cold pool.The balance of cold pool and environmental wind shear is favorable for the maintenance and strengthening of squall lines.展开更多
基金Supported by Qinghai Science and Technology Department Project(2020-ZJ-739,2019-ZJ-A10)National Key Research and Development Program of China(2018YFC1505705)+1 种基金National Natural Science Foundation of China(91637105,41475041)Key Project of Qinghai Procincial Meteorological Bureau(QXZ2020-03)。
文摘Based on the 4 times daily 0.75°×0.75°ERA-Interim data,the relationship between precipitation and a transverse shear line(TSL)over Qinghai-Tibet Plateau during August 15-19,2015 is analyzed.The results show that precipitation and TSL had obvious diurnal variation.That is,the intensity of the TSL and the precipitation tended to increase from afternoon to night and reduce from 00:00 to 06:00 UTC(the same below).The shape of the rain area was basically consistent with the direction of the TSL,and when the zonal characteristics of the rain area were obvious,the precipitation distribution was relatively uniform,otherwise the local short-term heavy precipitation was easy to occur.The precipitation center was basically consistent with the positive vorticity center near the TSL,and precipitation was directly proportional to the value of positive vorticity.The equation for the budget of vorticity shows that the horizontal advection term determined the moving direction of the TSL.The vertical transportation term determined the structural characteristics of the TSL on the vertical section,and positive vertical transport item of lower level was conducive to the formation of the plateau vortex.The horizontal convergence or divergence term determined the position of the TSL,and was conducive to the maintenance of the TSL.The evolution of apparent heat source and apparent water vapor sink near the TSL had a distinct diurnal feature.Meanwhile,atmospheric heating in the precipitation process was closely related to atmospheric upward movement,and the latent heat of condensation release caused by precipitation was beneficial to the maintenance of the plateau shear line and the formation and strengthening of plateau vortex.The precipitation of the TSL was mainly dominated by weak convective precipitation.
基金National Natural Science Foundation of China(41930972,52239006,41975001)。
文摘A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China,leading to heavy precipitation.We examined the differences in the mesoscale characteristics and microphysics of the frontal and warm sector rain belts that occurred in South China on May 10–13,2022.The southern rain belt occurred in an environment with favorable mesoscale conditions but weak large-scale forcing.In contrast,the northern rain belt was related to low-level horizontal shear and the surface-level front.The interaction between the enhanced southeasterly winds and the rainfall-induced cold pool promoted the persistent growth of convection along the southern rain belt.The convective cell propagated east over the coastal area,where there was a large temperature gradient.The bow-shaped echo in this region may be closely related to the rear-inflow jet.By contrast,the initial convection of the northern rain belt was triggered along the front and the region of low-level horizontal shear,with mesoscale interactions between the enhanced warm-moist southeasterly airflow and the cold dome associated with the earlier rain.The terrain blocked the movement of the cold pool,resulting in the stagnation of the frontal convective cell at an early stage.Subsequently,a meso-γ-scale vortex formed during the rapid movement of the convective cell,corresponding to an enhancement of precipitation.The representative raindrop spectra for the southern rain belt were characterized by a greater number and higher density of raindrops than the northern rain belt,even though both resulted in comparable hourly rainfalls.These results help us better understand the characteristics of double rain belts over South China.
基金Supported by the National Natural Science Foundation of China(91637105 and 41475041)National Science and Technology Support Program of China(2015BAC03B06)
文摘Based on the 4 times daily 0.75°× 0.75° ERA-Interim data, the structural evolution of a Qinghai-Tibetan Plateau horizontal (east-west-oriented) shear line (TSL) during 15-19 August 2015 and the effect of diabatic heating on its evolution were analyzed. The results show that the TSL possessed a vertical thickness of up to 1.5 km (approxim-ately 600-450 hPa), and was baroclinic in nature. Weak ascending motions occurred near the TSL, accompanied with more significant gradients in dew point temperature than in temperature. The TSL was characterized by diurnal vari- ations in its appearance and structure. It was relatively full in shape (broken) and was the lowest (highest) in vertical extent at 0000 (1800) UTC, and veered clockwise (anticlockwise) dttring 0000--0600 (1200-1800) UTC. When the north-south span of the TSL increased, it was prone to fracturing; and it disappeared when the dew point temperat-ure gradients to its either side decreased. When the TSL moved northward (southward), its western (eastern) section broke up, while the eastern (western) section inclined to regenerate or merge. The TSL tended to move towards the positive vorticity areas with significant increases in vorticity. When the positive vorticity center moved down, the height of TSL decreased. Further analysis shows that the plateau surface heating dominated the vorticity attribute of the TSL and its movement, with different contributions from local variation, horizontal advection, and vertical advec-tion of the diabatic heating to the TSL at different heights.
基金National Natural Science Foundation of China(41705029,41675045)Strategic Priority Research Program of Chinese Academy of Sciences(XDA17010105)Key R&D Projects of Anhui Province(201904a07020099)。
文摘The impacts of different moisture profiles on the structure and vertical motion of squall lines were investigated by conducting a set of numerical simulations.The base state was determined by an observational sounding,with high precipitable water representing moist environmental conditions in the East Asian monsoon region.To reveal the impact of moisture at different levels,the moisture content at the middle and low levels were changed in the numerical simulations.The numerical results showed that more convective cells developed and covered a larger area in the high moisture experiments,which was characteristic of the convection during the Meiyu season in China.In addition,high moisture content at low levels favored the development of updrafts and triggered convection of greater intensity.This was demonstrated by the thermodynamic parameters,including Convective Available Potential Energy(CAPE),Lifted Index(LI),Lift Condensation Level(LCL),and Level of Free Convection(LFC).Dry air at middle levels led to strong downdrafts in the environment and updrafts in clouds.This could be because dry air at middle levels favors the release of latent heat,thereby promoting updrafts in clouds and downdrafts in the environment.Therefore,high relative humidity(RH)at low levels and low RH at middle levels favors updrafts in the cloud cores.Additionally,moist air at low levels and dry air at middle levels promotes the development of convective cells and the intensification of cold pool.The squall line can be organized by the outflow boundary induced by cold pool.The balance of cold pool and environmental wind shear is favorable for the maintenance and strengthening of squall lines.