A Numerical Simulation Study of Mesoscale Rainy-Cluster Producing Heavy Rainfall in Lower Latitude Plateau during Early Summer

Based on the successful diagnostic study, numerical simulation was conducted for better understand of heavy rainfall in lower latitude plateau from 0000 UTC 31 May to 0000 UTC 1 June 2001. Due to successful reproducing of large-scale circulation, precipitation and rainy-cluster area, there existed the probability to study one of the rainy-clusters causing heavy rainfall by using the high resolution output data from the numerical model. It shows that the obvious mesoscale dynamical and thermodynamic structure inside the rainy-cluster defined as rainy-cluster A can be found during its development even though there was no obvious closed vortex in the wind field. The positive vortex maximum occurred earlier than rainy-cluster A, and the intensifying of ascending motion resulted from the horizontal convergence in the lower troposphere. The formation of rainy-cluster A was related not only to mesoscale convergence lines near the ground, but also to the special topography in the lower latitude plateau, especially, in Yunnan Province. The southern wind played an important role in the formation and the development of rainy-cluster A. And the appearance and evolution of rainy-cluster A was also related closely to the Indian-Myanmar trough at 500 hPa. The analysis of water vapor shows, there existed the pronounced horizontal and vertical water vapor convergence before the mature stage of rainy-cluster A, and the water vapor came mainly from the Bay of Bengal.