2004年初夏一次云南暴雨过程的中尺度系统及其水汽特征分析研究

A STUDY OF MESOSCALE SYSTEMS AND MOISTURE SUPPLY DURING A HEAVY RAINFALL IN YUNNAN IN EARLY SUMMER 2004

利用NCEP再分析资料、地面加密降水资料和风云-2卫星红外云图,对2004年云南初夏的一次强降水过程的大尺度环流背景、中尺度系统和水汽输送特征及来源情况进行了较为详尽的分析研究。结果表明:(1)高低空环流的有利配置、印缅槽与东亚冷槽的相互作用,为此次云南地区暴雨的产生提供了有利条件;(2)暴雨至少与四个连续生消的对流云团活动直接相关,强降水落区与云南的地形特征相关不大,只与低层辐合线有很好的一致性,而辐合线的发展演变与冷暖空气的势力对比相关;(3)对降水区三维结构的分析表明,中尺度对流系统强烈发展区的低层为强辐合、正相对涡度,高层为辐散、负相对涡度;中低层有较强的上升运动,低层湿度较大、有不稳定能量的蓄积和释放;(4)对云南水汽输送分析表明,直接影响此次云南强降水的水汽输送主要来源于孟加拉湾,并且引起此次云南强降水的水汽辐合是由风场辐合引起的,而水汽平流在这一地区为弱的干平流;同时,在较强的西南气流下,水汽辐合可存在于较高的气压层。

In this paper,by using the NCEP data,dense precipitation data and hourly satellite data,a detailed study was done of the large-scale circulation,meso-scale systems and vapor budget for a heavy rainfall in Yunnan during early summer 2004.Results show that the interaction between an Indian-Myanmar trough and an East Asian（thermodynamically） cold trough released instable energy and kept convection reappearing.The heavy rainfall was interrelated with four convective cloud clusters which were produced in succession.The position of precipitation was well consistent with mesoscale convergence lines,which were caused by interactions between cold and warm air.Analysis of the three-dimensional structure of precipitation systems shows that,in the lower troposphere,mesoscale convective systems developed,convergence was strong,and relative vorticity was positive,whereas in the upper troposphere,divergence was strong and relative vorticity was negative.There existed strong upward motion,rich water vapor as well as instable energy in the lower troposphere.Analysis of water vapor supply shows that a main source of water vapor for the heavy rainfall was situated in the Bay of Bengal.The convergence of water vapor was mainly caused by the convergence of wind field,and the advection of water vapor was dry.Meanwhile,water vapor,lifted by the terrain to the middle troposphere under strong southwest airstream,caused heavy rainfall.