Numerical Simulation Research On Characters Of β-mesoscale Convective System (M_βCSs) Of Storm Rainfall In Low Latitude Plateau Of China

Conventional observing data, automatic meteorological observing precipitation data from "973" program, TBB data, infrared satellite pictures, NCEP1°×1°reanalysis data and MM5(V3.6) mesoscale numerical model were used to simulate a heavy storm rainfall event happened on June 16 to 17 of 2003 in Low Latitude Plateau of China, which caused by M_βCSs, in order to investigate the structure characters of M_βCSs and their formation reasons. At the same time, the simulation on a case of June 20 to 21 during the lasting storm rainfall period in 2005 to compare M_βCSs structure characters with which happened in Low Latitude Plateau, and to find the regional features of M_βCSs in Low Latitude Plateau and main reasons of the features' forming.Analysis indicates that the water vapour contributing to this storm rainfall event in Low Latitude Plateau has different channels at different levels. On the layer of 500hPa, water vapour comes from Bay of Bengal only, and that comes from both Bay of Bengal and east of china on 700hPa. Convergence on lower layers and weak divergence on upper layers is the factor which leads to the formation of storm rainfall M_βCSs on June 16 of 2003 in Low Latitude Plateau of China. Severe potential equivalent temperature gradient on 700hPa～500hPa accumulates intensive unstable energy, which breaks out quickly. Upper level temperature's increasing makes the warm heart grove; which leads to the lifting of isobaric surface and the formation ofβ-mesoscale cyclonic disturbance on 500hPa. Then the lower level convergence and the upper level divergence strengthen further. The growth and the propagation of gravity wave lead to the fast dispersion of energy which causes the development of M_βCSs at the two sides of the mature M_βCSs and the fast weakening of precipitation.Comparing analysis indicates that physical quantities of the M_βCSs in Low Latitude Plateau are fleeter and weaker than that in the South of China which also locates at lower latitude. And the vertical axes of some physical factors such as divergence and moisture flux divergence tilt eastward with the increase of height. In Low Latitude Plateau, the life time of warm heart is shorter and the value of CAPE is smaller. Orographic sensitivity experiment indicates that terrain is the main factor of gravity wave's propagation and the reason of the formation of M_βCSs regional features in Low Latitude Plateau. The higher terrain height which causes the short water vapour air column is the main reason that the life time of warm center structure in Low Latitude Plateau region is shorter than that in downstream regions. These lead to the lifetime of M_βCSs in Low Latitude Plateau is relatively short and the precipitation breaks out immediately, and has short lifetime and severe intensity. And higher terrain height is beneficial for the propagation of gravity wave in Low Latitude Plateau of China.