Effects of a preexisting cold pool on the initiation of an extreme rainfall in southern Xinjiang

Abstract

On June 15, 2021, the Hotan region of southern Xinjiang was hit by an extreme rainfall event. A numerical simulation of the storm process, with a resolution of 3 km, was conducted to analyze the initiation mechanism of the rainfall. The results show that lifting conditions play a crucial role in triggering convection, compared to moisture and stratification conditions. The easterly jet changes the direction in the western part of the Tarim Basin and speeds up, creating a zone of high wind speeds in front of Kunlun Mountain's northern slope, which provides favorable conditions for convection initiation. A remarkable feature during this process is the effect of a preexisting distant cold pool on the southern slope of Tianshan Mountain. The cold pool impedes the easterly development of the easterly airflow in the basin, causing it to turn northward, and accelerates the mountain front airflow in front of Kunlun Mountain. The inner dynamic mechanism is a strengthening of the low-level horizontal pressure gradient between the cold pool and the low-pressure belt along Kunlun Mountain. The numerical sensitivity experiments also highlight the key role the distant cold pool plays in the development of the high-speed wind belt ahead of the mountain and causes convection to start 4 h earlier. These results will serve as a valuable reference for future studies on the formation process of convection and improve the understanding of precipitation forecast in arid and semi-arid regions.