Simulation of the Complex Terrain Influence on Summer Heavy Precipitation in Ailao Mountain

The weather research and forecasting model was adopted to simulate precipitation processes on 13 June and 14 June 2020, in the Ailao Mountain region of Yunnan Province. A discussion of the influence of the Ailao Mountain topography on the spatiotemporal distribution of heavy precipitation and its possible physical mechanism is presented through the comparative analysis of terrain sensitivity tests at different mountain heights. The following results were obtained: 1) Terrain sensitivity tests at different heights showed that terrain height affects the location of the low vortex shear line. 2) At high terrain elevation, the pseudo-equivalent potential temperature lines in the middle and low levels were denser, the gradient was larger, and water vapor and unstable energy rapidly accumulated. The accompanying strong upward motion may trigger severe convective weather in advance. With decreasing topographic height, the pseudo-equivalent potential temperature line was flat and evacuated. The local uplift and unstable energy of the Ailao Mountains were low and inadequate to trigger medium or small-scale severe convective weather. 3) In the WSM6 microphysics scheme, the variation of topographic height also has an obvious impact on the cloud microphysics process. At high terrain elevation, the forced uplift was strengthened, which made the ice crystal and snow mixture stay in the air longer and expand the range gradually. Consequently, a downdraft of secondary circulation was generated, and the cloud water and raindrops collided and strengthened in the middle and lower layers, leading to a decrease in the cloud water mixing ratio and an increase in the rain mixing ratio.