A squall line in front of the tropical cyclone Pabuk occurred in the west of the Pearl River Delta to Zhanjiang on August 8th, 2007 when the storm approached South China. The development, structure and environmental c...A squall line in front of the tropical cyclone Pabuk occurred in the west of the Pearl River Delta to Zhanjiang on August 8th, 2007 when the storm approached South China. The development, structure and environmental conditions for this squall line were investigated in this study, with particular attention paid to the possible connection of this squall line with Pabuk. The observational data employed in this study are from soundings, Doppler weather radars and wind profile radars. The following six major conclusions are drawn by our observational analyses.(1) This squall line developed gradually from individual convective cells, and land breeze may be responsible for the onset of the squall line.(2) The path and intensity of the squall line were modulated by the environmental conditions. The squall line propagated along the coastline, and it was stronger on the landing side of the coastline compared with the surrounding in-land regions and oceanic regions.(3) The typical characteristics of tropical squall lines were seen in this squall line,including the cold-pool intensity, vertical structure and the wake flow stratiform precipitation at its developing and mature phases.(4) The environmental conditions of this squall line resemble those of tropical squall lines in terms of deep moist air and low convection condensation level. They also resemble mid-latitude squall lines in terms of the convective instable energy and vertical wind shear in the lower troposphere.(5) Two roles were played by the strong wind around Pabuk. On the one hand, it made the atmosphere more unstable via suppressed shallow convection and increased solar radiation. On the other hand, it enhanced the land-sea thermal contrast and therefore strengthened the sea breeze and the resultant water vapor transport. The sinking temperature inversion prevented the occurrence of low-layer weak convection and accumulated convection instability energy for the development of the strong convection.展开更多
Influenced by strong winds associated with a southeastward-moving Mongolian cyclone,a severe transmission line galloping occurred in Baiyin City,Gansu Province,on 14 April 2020.This caused a tripping incident of the t...Influenced by strong winds associated with a southeastward-moving Mongolian cyclone,a severe transmission line galloping occurred in Baiyin City,Gansu Province,on 14 April 2020.This caused a tripping incident of the transmission line in this region.Based on the hourly,0.5°×0.5°,ECMWF ERA5 reanalysis data,this study investigated the formation mechanisms of the Mongolian cyclone and its associated strong winds.Results from the vorticity budget indicate that the convergence-related vertical stretching and the upward transport of cyclonic vorticity governed formation of the Mongolian cyclone in this event;whereas,tilting and export of cyclonic vorticity from the central region of the cyclone mainly decelerated the cyclone’s formation.The kinetic energy(KE)budget shows that the wind associated with the Mongolian cyclone was mainly enhanced by the positive work of the pressure gradient force.Unlike some typical strong wind events in Northwest China,during this event,no significant downward momentum transportation from the upper troposphere was found.The vertical transport of KE exerted a slightly favorable effect on the KE increase around the location where the transmission line galloping trip appeared.In contrast,the horizontal transport mainly caused an export of KE from this region,which applied an overall negative effect on the wind enhancement associated with the Mongolian cyclone.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
利用华东区域实况自动观测资料和全球预报系统的FNL再分析资料对一次爆发性气旋及其引发的大风天气进行诊断分析,结果发现,由高空急流调整导致叠加在气旋上空的中层辐散区,中高层干冷空气伴随正涡度,沿西北气流下传并在低层侵入气旋后部...利用华东区域实况自动观测资料和全球预报系统的FNL再分析资料对一次爆发性气旋及其引发的大风天气进行诊断分析,结果发现,由高空急流调整导致叠加在气旋上空的中层辐散区,中高层干冷空气伴随正涡度,沿西北气流下传并在低层侵入气旋后部,气旋前部850 h Pa西南急流输送的暖湿气流和气旋西侧槽前西南急流输送的暖湿气流通过潜热释放共同促成气旋的爆发性发展;同时在气旋发展初期,高层高湿位涡区的向下传输,也加速了气旋的快速发展。气旋第三象限的大风由动量下传触发强对流并形成大风叠加所致,低层西北干冷气流切断低层的增湿,使大风区降雨很弱。低层切变线与地面带状CAPE高值区重合,该区域未来1~2 h将出现大风,对预报有明显的指示意义。展开更多
基金National Natural Science Foundation of China(91215302,51278308)Open Project for State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry,Institute of Atmospheric Physics(LAPC)
文摘A squall line in front of the tropical cyclone Pabuk occurred in the west of the Pearl River Delta to Zhanjiang on August 8th, 2007 when the storm approached South China. The development, structure and environmental conditions for this squall line were investigated in this study, with particular attention paid to the possible connection of this squall line with Pabuk. The observational data employed in this study are from soundings, Doppler weather radars and wind profile radars. The following six major conclusions are drawn by our observational analyses.(1) This squall line developed gradually from individual convective cells, and land breeze may be responsible for the onset of the squall line.(2) The path and intensity of the squall line were modulated by the environmental conditions. The squall line propagated along the coastline, and it was stronger on the landing side of the coastline compared with the surrounding in-land regions and oceanic regions.(3) The typical characteristics of tropical squall lines were seen in this squall line,including the cold-pool intensity, vertical structure and the wake flow stratiform precipitation at its developing and mature phases.(4) The environmental conditions of this squall line resemble those of tropical squall lines in terms of deep moist air and low convection condensation level. They also resemble mid-latitude squall lines in terms of the convective instable energy and vertical wind shear in the lower troposphere.(5) Two roles were played by the strong wind around Pabuk. On the one hand, it made the atmosphere more unstable via suppressed shallow convection and increased solar radiation. On the other hand, it enhanced the land-sea thermal contrast and therefore strengthened the sea breeze and the resultant water vapor transport. The sinking temperature inversion prevented the occurrence of low-layer weak convection and accumulated convection instability energy for the development of the strong convection.
基金supported by the National Key R&D Program of China grant number 2018YFC0809400the science and technol-ogy foundation of State Grid Corporation of China grant number5200-202016243A-0-0-00the Innovation Fund of China Electric Power Research Institute grant number NY83-19-002。
文摘Influenced by strong winds associated with a southeastward-moving Mongolian cyclone,a severe transmission line galloping occurred in Baiyin City,Gansu Province,on 14 April 2020.This caused a tripping incident of the transmission line in this region.Based on the hourly,0.5°×0.5°,ECMWF ERA5 reanalysis data,this study investigated the formation mechanisms of the Mongolian cyclone and its associated strong winds.Results from the vorticity budget indicate that the convergence-related vertical stretching and the upward transport of cyclonic vorticity governed formation of the Mongolian cyclone in this event;whereas,tilting and export of cyclonic vorticity from the central region of the cyclone mainly decelerated the cyclone’s formation.The kinetic energy(KE)budget shows that the wind associated with the Mongolian cyclone was mainly enhanced by the positive work of the pressure gradient force.Unlike some typical strong wind events in Northwest China,during this event,no significant downward momentum transportation from the upper troposphere was found.The vertical transport of KE exerted a slightly favorable effect on the KE increase around the location where the transmission line galloping trip appeared.In contrast,the horizontal transport mainly caused an export of KE from this region,which applied an overall negative effect on the wind enhancement associated with the Mongolian cyclone.
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.
文摘利用华东区域实况自动观测资料和全球预报系统的FNL再分析资料对一次爆发性气旋及其引发的大风天气进行诊断分析,结果发现,由高空急流调整导致叠加在气旋上空的中层辐散区,中高层干冷空气伴随正涡度,沿西北气流下传并在低层侵入气旋后部,气旋前部850 h Pa西南急流输送的暖湿气流和气旋西侧槽前西南急流输送的暖湿气流通过潜热释放共同促成气旋的爆发性发展;同时在气旋发展初期,高层高湿位涡区的向下传输,也加速了气旋的快速发展。气旋第三象限的大风由动量下传触发强对流并形成大风叠加所致,低层西北干冷气流切断低层的增湿,使大风区降雨很弱。低层切变线与地面带状CAPE高值区重合,该区域未来1~2 h将出现大风,对预报有明显的指示意义。
