The climatological distribution of mesoscale convective systems (MCSs) over China and its vicinity during summer is statistically analyzed, based on the 10-year (1996―2006, 2004 excluded) June-August infrared TBB (Te...The climatological distribution of mesoscale convective systems (MCSs) over China and its vicinity during summer is statistically analyzed, based on the 10-year (1996―2006, 2004 excluded) June-August infrared TBB (Temperature of black body) dataset. Comparing the results obtained in this paper with the distribution of thunderstorms from surface meteorological stations over China and the distribution of lightning from low-orbit satellites over China and its vicinity in the previous studies, we find that the statistic characteristics of TBB less than -52℃ can better represent the spatiotemporal distribution of MCSs over China and its vicinity during summer.The spreading pattern of the MCSs over this region shows three transmeridional bands of active MCSs, with obvious fluctuation of active MCSs in the band near 30°N. It can be explained by the atmospheric circulation that the three bands of active MCSs are associated with each other by the summer monsoon over East Asia. We focus on the diurnal variations of MCSs over different underlying surfaces, and the result shows that there are two types of MCSs over China and its vicinity during summer. One type of MCSs has only one active period all day long (single-peak MCSs), and the other has multiple active periods (multi-peak MCSs). Single-peak MCSs occur more often over plateaus or mountains, and multi-peak MCSs are more common over plains or basins. Depending on lifetimes and active periods, single-peak MCSs can be classified as Tibetan Plateau MCSs, general mountain MCSs, Ryukyu MCSs, and so on. The diurnal variation of multi-peak MCSs is very similar to that of MCCs (mesoscale convective complexes), and it reveals that multi-peak MCSs has longer life cycle and larger horizontal scale, becomes weaker after sunset, and develops again after midnight. Tibetan Plateau MCSs and general mountain MCSs both usually develop in the afternoon, but Tibetan Plateau MCSs have longer life cycle and more active MαCSs. Ryukyu MCSs generally develop after midnight, last longer t展开更多
The analyses of spatial and temporal characteristics of positive cloud-to-ground(CG)lightning for four mesoscale convective systems and two severe local convective systems in 1989 and 1990 show that positive CG flash ...The analyses of spatial and temporal characteristics of positive cloud-to-ground(CG)lightning for four mesoscale convective systems and two severe local convective systems in 1989 and 1990 show that positive CG flash rate usually has two peak values.The major peak occurs during the developing stage of the storm and most of the positive CG flashes originate at the lower part of the storm.The minor occurs during the dissipative stage of the storm and most of the positive CG flashes originate at the upper part of the storm,especially in the region of the wind divergence in the storm anvil.The positive CG flash rate is almost an order of magnitude larger in the developing stage than in the dissipative stage.The appearing time of the peak of negative CG flash rate is in accordance with that of the valley of pos- itive CG flash rate. The higher the intensity of the radar echo,the higher the positive CG flash rate.Most of the positive CG flashes oc- cur when the weak echo area is larger,and mostly originate in the region where the radar echo intensity is about 10dBz and in the back region of the moving storms.The spatial distribution of the positive CG flashes is much more dispersive than that of the negative.The mesoscale analysis reveals a bipolar lightning pattern.The mean bipole--length reaches its minimum during the mature stage of the storm and reaches the maximum during the developing stage of the storm. The vertical distribution of the charge density is calculated by a one-dimensional charging model.Then,we discuss the producing condition of the positive CG lightning and forming cause of charge structure mentioned above.展开更多
利用NCEP/CFSR 0.5°×0.5°再分析资料、FY-2G卫星TBB云图资料、华南雷达拼图、雷达TREC风等资料,对2016年5月20日广东信宜特大暴雨过程的中尺度对流系统特征进行了分析。结果表明:(1)信宜特大暴雨过程中强降水持续近8 h,...利用NCEP/CFSR 0.5°×0.5°再分析资料、FY-2G卫星TBB云图资料、华南雷达拼图、雷达TREC风等资料,对2016年5月20日广东信宜特大暴雨过程的中尺度对流系统特征进行了分析。结果表明:(1)信宜特大暴雨过程中强降水持续近8 h,平均每小时雨量超过50 mm,1 h最大雨强出现在中午12时(北京时,下同),达132.8 mm。(2)对流层高层250 h Pa一直维持强辐散区,500 h Pa中低纬低槽以及925 h Pa低涡缓慢移动、超低空暖湿急流不断增强等有利的大气环流背景是强降水得以维持的原因。强烈的垂直上升运动,有利的大气不稳定状态以及水汽辐合条件是信宜出现极端强降水的诱因之一。(3)稳定的大气环流背景使云顶亮温(TBB)≤-52℃的中尺度对流云团和云顶亮温(TBB)≤-72℃的对流活动中心在信宜上空长时间维持,进而引发特大暴雨过程。(4)特大暴雨主要经历了两个阶段:先发生于两条回波带的交汇处,然后产生在东西向的带状回波上。强降水回波较长时间不断地经过,产生"列车效应",是导致信宜特大暴雨的主要原因。(5)40 d Bz以上回波都在-10℃层、甚至0℃层高度以下,最强回波中心在2 km高度附近,这种质心较低的对流降水系统,降水效率较高,有利于暴雨增强。回波顶高发展到19 km,-10℃以上存在一个深厚的冰相增长带,有利于形成大量的冰晶或霰粒子及冰晶淞附成大冰晶,降落时形成大雨滴,导致暴雨瞬时强度大。(6)雷达TREC风场显示,特大暴雨发生在喇叭口地形附近、超低空急流的左侧、中尺度辐合线上和中尺度低涡中心附近。展开更多
基金the National Major Basic Research "973" Program of China (Grant No. 2004CB418300)the National Natural Science Foundation of China (Grant No. 40305004)
文摘The climatological distribution of mesoscale convective systems (MCSs) over China and its vicinity during summer is statistically analyzed, based on the 10-year (1996―2006, 2004 excluded) June-August infrared TBB (Temperature of black body) dataset. Comparing the results obtained in this paper with the distribution of thunderstorms from surface meteorological stations over China and the distribution of lightning from low-orbit satellites over China and its vicinity in the previous studies, we find that the statistic characteristics of TBB less than -52℃ can better represent the spatiotemporal distribution of MCSs over China and its vicinity during summer.The spreading pattern of the MCSs over this region shows three transmeridional bands of active MCSs, with obvious fluctuation of active MCSs in the band near 30°N. It can be explained by the atmospheric circulation that the three bands of active MCSs are associated with each other by the summer monsoon over East Asia. We focus on the diurnal variations of MCSs over different underlying surfaces, and the result shows that there are two types of MCSs over China and its vicinity during summer. One type of MCSs has only one active period all day long (single-peak MCSs), and the other has multiple active periods (multi-peak MCSs). Single-peak MCSs occur more often over plateaus or mountains, and multi-peak MCSs are more common over plains or basins. Depending on lifetimes and active periods, single-peak MCSs can be classified as Tibetan Plateau MCSs, general mountain MCSs, Ryukyu MCSs, and so on. The diurnal variation of multi-peak MCSs is very similar to that of MCCs (mesoscale convective complexes), and it reveals that multi-peak MCSs has longer life cycle and larger horizontal scale, becomes weaker after sunset, and develops again after midnight. Tibetan Plateau MCSs and general mountain MCSs both usually develop in the afternoon, but Tibetan Plateau MCSs have longer life cycle and more active MαCSs. Ryukyu MCSs generally develop after midnight, last longer t
基金supported by grants from State Planning Commission under grants No.75-09-02-19
文摘The analyses of spatial and temporal characteristics of positive cloud-to-ground(CG)lightning for four mesoscale convective systems and two severe local convective systems in 1989 and 1990 show that positive CG flash rate usually has two peak values.The major peak occurs during the developing stage of the storm and most of the positive CG flashes originate at the lower part of the storm.The minor occurs during the dissipative stage of the storm and most of the positive CG flashes originate at the upper part of the storm,especially in the region of the wind divergence in the storm anvil.The positive CG flash rate is almost an order of magnitude larger in the developing stage than in the dissipative stage.The appearing time of the peak of negative CG flash rate is in accordance with that of the valley of pos- itive CG flash rate. The higher the intensity of the radar echo,the higher the positive CG flash rate.Most of the positive CG flashes oc- cur when the weak echo area is larger,and mostly originate in the region where the radar echo intensity is about 10dBz and in the back region of the moving storms.The spatial distribution of the positive CG flashes is much more dispersive than that of the negative.The mesoscale analysis reveals a bipolar lightning pattern.The mean bipole--length reaches its minimum during the mature stage of the storm and reaches the maximum during the developing stage of the storm. The vertical distribution of the charge density is calculated by a one-dimensional charging model.Then,we discuss the producing condition of the positive CG lightning and forming cause of charge structure mentioned above.
文摘利用NCEP/CFSR 0.5°×0.5°再分析资料、FY-2G卫星TBB云图资料、华南雷达拼图、雷达TREC风等资料,对2016年5月20日广东信宜特大暴雨过程的中尺度对流系统特征进行了分析。结果表明:(1)信宜特大暴雨过程中强降水持续近8 h,平均每小时雨量超过50 mm,1 h最大雨强出现在中午12时(北京时,下同),达132.8 mm。(2)对流层高层250 h Pa一直维持强辐散区,500 h Pa中低纬低槽以及925 h Pa低涡缓慢移动、超低空暖湿急流不断增强等有利的大气环流背景是强降水得以维持的原因。强烈的垂直上升运动,有利的大气不稳定状态以及水汽辐合条件是信宜出现极端强降水的诱因之一。(3)稳定的大气环流背景使云顶亮温(TBB)≤-52℃的中尺度对流云团和云顶亮温(TBB)≤-72℃的对流活动中心在信宜上空长时间维持,进而引发特大暴雨过程。(4)特大暴雨主要经历了两个阶段:先发生于两条回波带的交汇处,然后产生在东西向的带状回波上。强降水回波较长时间不断地经过,产生"列车效应",是导致信宜特大暴雨的主要原因。(5)40 d Bz以上回波都在-10℃层、甚至0℃层高度以下,最强回波中心在2 km高度附近,这种质心较低的对流降水系统,降水效率较高,有利于暴雨增强。回波顶高发展到19 km,-10℃以上存在一个深厚的冰相增长带,有利于形成大量的冰晶或霰粒子及冰晶淞附成大冰晶,降落时形成大雨滴,导致暴雨瞬时强度大。(6)雷达TREC风场显示,特大暴雨发生在喇叭口地形附近、超低空急流的左侧、中尺度辐合线上和中尺度低涡中心附近。
