Numerical simulation of circulation characteristics of orographic precipitation in Qilian Mountains, Northeastern Tibetan Plateau

In order to clarify the synoptic meteorology and low-level circulation characteristics of orographic precipitation in northeastern Tibetan Plateau (referred as TP), numerical simulation of a precipitation case that happened in Qilian Mountains on August 12-13, 2019 was conducted using the Weather Research and Forecasting (WRF) model in this paper. The results show that WRF model can roughly capture the timing and location of the orographic precipitation. During the period, a weak trough and a weak ridge were found behind a large-scale trough at 500 hPa at the initial and continuation phases primarily due to the effect of complicated topography to provide a beneficial circulation background at high altitudes. The extinction of this circulation pattern and northwesterly after the large-scale trough leaded to the extinction of the precipitation. In lower levels, warm advection from the south and cold advection from the north met over the precipitation region, resulting to a dividing temperature line tilting northeast from surface to high-altitude, which was crucial for instability and humidity, although no significant converging wind field near the surface suffering from the complex topography. In addition, the low-level jet, downslope flow and heating role at the basin bottom were also found to play important roles in the precipitation. The above analysis indicates that the precipitation was a result under the combined influence of the westerly circulation and the plateau monsoon circulation.