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

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.