Diagnostic Analysis of Heavy Rain Caused by a Low Vortex

An event with the maximum precipitation in the Meiyu period of WenZhou in 2007 is generally analyzed based on the conventional observation data and the 1°×1° NCEP/NCAR reanalysis data.The moving vortex is the efficient reason for causing the local heavy rain.It is hard to forecast the area,the intensity and the total precipitation of the heavy rain caused by a vortex in practice.By analyzing the pattern development,the influencing system and the physical parameter field,some forecasts respect of heavy rain caused by a vortex and the characteristics of the physical parameter are summarized,it is found that the heavy rain usually occures in front and the right area of the vortex,there are corresponding relationship between the area of the heavy rain and negative center of the moisture flux divergence.It is also found that the moisture of the heavy rain happened in costal area and inland area is derived from different places,the South China Sea and the North Pacific Ocean are the two moisture sources of the heavy rain.The heavy rain caused by the vortex is reinforced by the easterly airflow which comes from the North Pacific Ocean.As the dynamical condition,the strong upward current in middle-level and low-level layer in front of the vortex is in favor of the persistent heavy rain in the costal area of south ZheJiang.