To study the mesoscale convective systems (MCSs) and the characteristics of environment field of a heavy rainfall process occurred in Sichuan Basin on early July 2013, data of conventional surface and sounding observation stations, meteorological automatic stations as well as the associated NCEP FNL (1°×1°) final analysis data are employed in this paper for synoptic meteorological analysis. It is shown that the rainfall process contains three stages corresponding to the generation and evolution of three different MCSs. The 700 hPa shear line and 850 hPa low vortex provide favorable dynamical conditions for the generation of MCSs. MCSs in the three stages all locate along the 700 hPa shear line or near 850 hPa low vortex center and all coincide with the evolution of low-level systems very well. Cold Air intrusion is very important to the evolution of MCSs in the Sichuan Basin's heavy rainfall event. Both the initiation time and spatial distribution of heavy rainfall are closely related to the intrusion of cold air. The results also show that topography of Sichuan Basin has two aspects of effects on the generation of MCSs. On one side, topography could result in strong ascending motions at mountain front areas, while on the other side it may induce strong thermal contrast between cold and warm air by accumulating cold air which could enhance the frontogenesis.
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