A Study of Circumstances of Meso-β-Scale Systems of Strong Heavy Rainfall in Warm Sector Ahead of Fronts in South China
A Study of Circumstances of Meso-β-Scale Systems of Strong Heavy Rainfall in Warm Sector Ahead of Fronts in South China
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发表时间：
2006
影响因子：
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通讯作者：
Xiao-Ying Ru;Zhao Si
中科院分区：
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作者：
Xiao-Ying Ru;Zhao Si
珠江致洪暴雨的环流特征及影响系统对2005年6月西江流域暴雨过程进行了分析，结果表明：该次暴雨过程具有明显的多尺度系统特征，且发生在锋前暖区，与季风活动、边界层的影响和地形的动力抬升有关。（1）南海季风爆发较晚，对华南影响持续，西风带高空急流位置偏南，副高维持在18°N，为华南暴雨的持续提供了非常有利的大尺度环流。(2)前汛期华南锋前暖区有强暴雨发生，在华南锋前暖区始终存在一个近东西向的准西风带，锋生函数的计算结果表明，较弱冷空气对暴雨的发生起着重要作用，水平风垂直剖面和垂直速度的分析表明，锋面前方有明显的上升运动，这对中尺度对流的形成和发展非常有利，来自北方的较弱冷空气与沿副热带高压西南缘沿着来的暖湿空气相互作用，存在中低纬系统的相互作用。(3)低层西南风的风速辐合在925 hPa处最为明显，表明行星边界层在这次暴雨的形成中起了重要作用，气流不仅从中印半岛和南海向暴雨区输送了充足的水汽，而且对对流的发生也有贡献。(4)南岭山脉的喇叭形地形增强了南来暖湿空气的上升运动，有利于强降水的发生，而华南地区特别是西江流域的特殊地形是造成持续性强降水的重要条件之一。(5)中尺度对流雨团是此次暴雨的直接影响系统，西江流域至少存在4个中β尺度雨团（A、B、C、D），其中A、D雨团位于桂林、梧州观测站附近，因此，可以对A、D雨团的环境进行细致的研究，其雨区与低层辐合中心有密切的联系，而与辐合中心有密切的联系，这两个雨团的雨区与辐合中心有密切的联系。在这种情况下，中尺度对流系统和暴雨非常活跃，而且对流雨团跟随洪峰即向下游移动，造成暴雨与洪峰的“耦合”，从而带来非常严重的灾害。(6)在此基础上，给出了前汛期华南锋前暖区强降水的影响因子示意图。
The circulation characteristics and the influencing systems of the heavy rainfall causing flood in the Pearl River(the Xijiang River) valley in June 2005 are investigated.The heavy rainfall had the outstanding characteristics of multi-scale systems and it occured in warm sector ahead of the front,relating to monsoon activity,the influence of the planetary boundary layer and the dynamic lifting of the topography.The conclusions are as follows:(1) The late onset of the South China Sea monsoon and its continuous impact on the South China,as well as the further south position of the upper-level jet in the westerlies and the subtropical high,which maintained in 18°N,provided the very favorable large-scale circulations for sustaining the heavy rainfalls in South China.(2) There were the heavy rainfalls happening in warm sector ahead of the front in South China during the pre-rainy season.There always existed an approximately east-to-west oriented quasi-stationary front in South China.The calculated results of the frontogenesis function indicate that the weaker cold air played an important role in occurrence of heavy rainfall.The analysis of the vertical cross section of horizontal wind and vertical velocity indicates that there was ascending motion obviously ahead of the front,which was very favorable for the formation and development of the meso-scale convection.The weaker cold air from the north interacted with the warm and wet air coming along the south-west edge of the subtropical high,there is a kind of interaction between middle- and low-latitude systems.(3) The wind speed convergence of south-west wind at low level was the most obvious at 925 hPa.It indicates that the planetary boundary level played an very important role in the formation of the heavy rainfall,the current not only transported sufficient water vapor to the heavy rainfall area from the Sino-Indian Peninsula and the South China Sea,but also contributed to the initiation of the convection.(4) The trumpet-shaped terrain in the Nanling Mountains enhanced the ascending motion of the warm and wet air from the south,which benefited the occurrence of the heavy rainfall.The special terrain in South China,especially in the Xijiang River valley,can be one of the important conditions for the appearance of the continuous heavy rainfalls.(5) The meso-scale convective rainy clusters were the direct influencing systems of the heavy rainfall.There were at least four meso-β-scale rainy clusters existing over the Xijiang River valley(A,B,C,D).Fortunately,A and D rainy clusters were located near Guilin and Wuzhou observation stations,respectively.So the environment of A and D rainy clusters can be carefully studied.The rainfall areas closely related to the convergence center of the low-level wind speed,and the convective available potential energy is cumulated,released and rebuilt again and again.Under such circumstances,the meso-scale convective system and heavy rainy were very active.Furthermore,the convective rainy clusters followed the flood peak,namely moved towards the lower reaches of the river,resulting in the "coupling" between the heavy rainfall and the flood peak,then brought the very serious disasters.(6) Based on the above-mentioned research,a schematic diagram of the influencing factors for the heavy rainfall in warm sector ahead of the front in South China during the period of pre-rainy season is given.