Abstract:A numerical simulation on the effect of the Tibetan Plateau on weather systems in the neighborhood area was carried out by LASG η-coordinate limited area mesoscale model (LASG MM).Two cases of heavy rain storms on April 28 and August 19,1998 were investigated under the topography with different relative heights.Study is mainly concentrated on the geopotential height fields,the temperature fields and streamline fields of 500hPa and 200hPa.Among the three kinds of fields,the temperature field suggests a large variation.When the relative height of the plateau is reduced,the temperature over the plateau goes up,and the temperature over the Sichuan Basin goes down.The magnitude of variation is larger in spring than that in summer.With lower relative heights,the large scale weather system over the plateau is strengthened,but the weather systems with middle or small scale are weakened over the plateau.On the other hand,the geopotential heights is reduced and the weather systems with small scale are strengthened over Sichuan Basin.Effect of the plateau with different relative heights on the streamline fields is similar to that of the goepotential field.With the influence of the forced wave and the lee wave,the streamline fields suggest the largest variation over the intersection area of the plateau and basin,which is exactly where the relative height changes most greatly.