Abstract:Based on FNL reanalysis data and hourly precipitation data converted from both regional meteorological station and CMORPH and using the method of high resolution WRF numerical simulation, this paper analyzes a typical short time local heavy rain process triggered by easterly mobile southwest vortex and complex terrain located in the northeast of Hubei in 22-24 July 2015. Further study is made on possible effect mechanism of how the mesoscale topography affects the increment of local rainfall. The result shows that the increment process of local rainfall was under the influence of the special topography in the middle lower reaches of Yangtze River, coupled with the effect of transportation of moist air in the front of southwest vortex. The two items worked together, triggering the weather process. The duration of local rainfall was short, but the increment was obvious. By researching the effect mechanism of single terrain on the local rainfall, we found that the Dabie Mountain’s terrain height impacted increment and scope of local severe rainfall positively, while the Mufu Mountain’s terrain height influenced the increment and scope of local rainfall negatively. As for the effect of Dabie Mountain’s terrain on the rainfall, the terrain was advantageous to reinforcement of convective instability, reinforcement of wind convergence and vertical shear, as well as maintenance and reinforcement of cold pool in lower troposphere. Different from Dabie Mountain’s terrain, Mufu Mountain’s terrain obstructed southerly moisture flow, then decreased the transportation of vapor flux above the rainfall area, which was unfavorable for increment of local rainfall. In addition, by researching the effect mechanism of the combined terrain on the local rainfall, we found the trumpet shaped topography consisting of Dabie Mountain’s terrain, Mufu Mountain’s terrain, Wannan Mountain’s terrain, and river valley between Mufu Mountain and Wannan Mountain, which forced the southerly airflow into terrain area to converge. What’s more, the river valley between Mufu Mountain and Dabie Moutain acted as an important channel for the southerly airflow to flow back into the Jianghan Plain from the east of Mufu Mountain, which effectively guaranteed the positive vorticity advection to be transported into the heavy precipitation area. In a word, the above favorable terrain configuration resulted in the increment of local severe rainfall.