Simulation Of Precipitation Over The Southern Slopes Of The Tibetan Plateau In Summer Based On The WRF Model

The Tibetan Plateau (TP) has great influences on the weather and climate of Asia and the world. It’s difficult to study the southern slopes of the TP because of its steep and complex terrain. However, the transportation and convergence processes of water vapor in the south margin of the TP play a decisive role in the distribution of precipitation over the TP and its surrounding area. Based on the analysis of the precipitation and the climatic characters over the southern slopes of the TP in 2006, impacts of cumulus parameterization schemes, two-way grid nesting approach and model resolution on the simulation of summertime precipitation over the steep southern slopes of the TP and its related reasons have been studied by using mesoscale numerical WRF V3.6.1 model.The maximum precipitation over the southern slopes of the TP in 2006 occurs in July, which mainly determines the distribution of the averaged summer precipitation. The platform of the TP lacks rainfall, while the precipitation over the slopes and its southern regions increases sharply. The precipitation over the southern slopes of the TP in summer is related to the divergence of the South Asia High, low-level flow field and the strong heating effect at the TP’s surface, as well as the transportation and convergence of the water vapor from the north Indian Ocean.The simulation analysis of the precipitation over the southern slopes of the TP in July 2006 shows that it is very sensitive to the selection of cumulus parameterization schemes, the differences of the results simulated by different schemes are significant. The comparison finds that the result simulated by Grell-Devenyi mass flux scheme is closer to the observed data in precipitation rate, the spatial distribution and the temporal evolution. Different cumulus parameterization schemes have great influences on the wind field and the humidity of low-level atmosphere, they can also affect the vertical heating profiles that leads to different convection and improve the intensity and distribution of the vertical velocity.Based on Grell-Devenyi scheme and by comparison of five kinds of sensitivity experiments, it is demonstrated that the use of cumulus parameterization scheme, the increasing of model resolution, and the application of two-way nesting approach can improve the simulated intensity and spatial distribution of precipitation, the simulated precipitation is closer to the observed one when these three approaches were used in combination. They can not only improve the simulated wind field and water vapor which makes the condition of water vapor more accurate; but also can affect the distribution of heating in the atmosphere, the potential stability and the vertical motion.The analysis of the severe weather process shows that WRF model is also good at simulating the occurrence and development processes of the meso-micro scale heavy rainfall. This study thus recommends a better scheme for the simulation studies of the precipitation over the southern slopes of the TP while using the WRF model.