The orographic dynamic effect plays an important role in the generation and development of local cloud and rainfall. Due to the Tianshan Mountain acting on focusing and lifting the westerly or northerly flow, the cloud and rainfall most focus on the west of Tianshan Mountain (trumpet-shaped) and the middle of its north slope (east-west towards) area in Xinjiang. Sensitivity tests of a typical heavy rainfall event occurred along the Tianshan Mountain from 24th to 26th August 2013 with different terrain height have been carried out employing the Weather Research and Forecasting (WRF) model to study the influence of the Tianshan Mountain' orographic dynamic effect on summer rainfall. The results show that the simulated spatial distribution, the position and the starting and ending time of the rainfall centers and maximum rainfall height of the control test are relatively consistent with one of observations, which means the model outputs can reflect the characteristics of the orographic precipitation in Tianshan Mountain to some extent. It come a general conclusion that the terrain height play slight roles in the rainfall distribution, whereas significant in the area coverage and grades of the heavy rainfall centers by comparing the control test results and the sensitivity ones. The precipitation is closely related to the relative size between the terrain height and the lift convective level (LCL). Owing to the remarkable blocking and uplifting role of the Tianshan Mountain, the prevailing airflow was lifted upward strongly, the instability release fully and more coagulations generate and maintain when the flow came to even exceeded the LCL, which resulted in the remarkable precipitation enhancement on the windward slope of the Tianshan Mountain. The topography plays little role in the distribution of the main coagulations (namely snow and ice) while remarkable in the center value and maintainance.
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