A Study of Convective Rainstorms along the East Slope of Western Sichuan Plateau

With conventional rain gauge data, radio-soundings, and NCEP 1°×1° reanalysis data, 12 rainstorm events along the east slope of the western Sichuan Plateau during 2004-2010 were analyzed. The weather patterns and environmental parameters during the formation and development of the convective rainstorms were investigated and the role of the western Sichuan Plateau in the formation of the convective rainstorms was evaluated. A set of idealized numerical simulations of the area’s topography were carried out to verify the results based on observations and the WRF mesoscale numerical model and the mean vertical profile calculated from plateau-upstream radio-soundings of the 12 convective rainstorms. The results are as follows: The plateau low pressure system moving into the Sichuan Basin is the main weather occurrence affecting the topographically convective rainstorm formation and development. With a low system moving into the Sichuan Basin, the southwest (south) flow in the lower troposphere evolves into a southeast (east) flow, the occurrence of which is the main cause of the topographically convective rainstorm formation. The air column contains sufficient moisture and convective available potential energy (CAPE) for the formation and development of the topographically convective rainstorm. The CAPE shows a clear diurnal variation with a peak phase during 1400LST to 2000LST, which is beneficial to the convective rainstorm formation and development. Due to the topographic Fr of the lower southeast (east) flow being slightly less than 1, the forced ascent and blocking of the around-flow may coexist when the air flows up the plateau. The air flow climbing in the topographical buffer zone and the cyclonic shear induced from the around-flow are both favorable for the initiation and development of the convective rainstorms. Lastly, a physical concept model is developed for the convective rainstorm formation in the buffer zone of the western Sichuan Plateau.