Impact of the Qinghai-Tibet Plateau Weather System on the Rainstorm on the North Slope of Kunlun Mountain

Based on the encryption automatic station data, the conventional ground and high altitude observation data, the FY2 static satellite data, and the initial field data of the ECMWF fine grid forecast model (spatial resolution 0.125 °× 0.125 °) in Tarim Basin in the southern Xinjiang, the rare rainstorm process occurred on the north slope of Kunlun Mountains from 24-26 June 2019 is analyzed. Aiming at the circulation situation, the weather system and the configuration of the high and low altitude systems, the plateau weather systems such as the Qinghai-Tibet high pressure, the plateau low vortex and shear line, and the jet stream south of the plateau were analyzed. Their important effects of the formation of Rainstorm on the northern slope of Kunlun Mountain is concluded as follows:

(1) The development and maintenance of the Qinghai-Tibet Plateau weather system are generated during favorable weather-scale dynamic and thermal processes, which are mainly manifested in the following three aspects: First of all, the South Asian High pressure changed from a double type to Qinghai-Tibet high pressure at 100hPa. At 200 to 300hPa, the southwestern jet stream lifted northward from the plateau and strengthened in the Tarim Basin in the southern Xinjiang. Suction effect can promote the ascending movement over the rainstorm area; Secondly, the low value system of the shear line nearly in the north-south direction between the Qinghai-Tibet high, the plateau vortex, the shear line and the Indian low is stable in 500hPa. The southerly flow prevails in the periphery of the West Pacific subtropical high, which runs through the Qinghai-Tibet Plateau and the South Xinjiang basin from the Bay of Bengal. The positive vorticity advection and warm advection on the southerly flow over the Qinghai-Tibet Plateau are conducive to the large-scale uplift movement over the rainstorm area and the western part of South Xinjiang, forming water vapor channel from south to north. While warm air transporting to the north, the North-South cold and warm air convergence is enhanced. Thirdly, the coupling between strong high-level divergence and middle-level convergence during heavy rains can result in enhanced mid-level water vapor convergence and vertical water vapor transport.

 (2) Weather systems below 600hPa have positive feedback on the maintenance and development of plateau weather systems. Easterly airflow was in the Tarim Basin in the southern Xinjiang between 600hPa and 700Pa，and the airflow at 600hPa was stronger than 700hPa. The easterly airflow carried part of the cold air into the Tarim Basin in the southern Xinjiang. A cold pad was formed in the lower layer below 600hPa in the southern Xinjiang basin, which facilitated the transfer of warm and humid air northward by the 500hPa middle-south wind and the 500 to 200hPa ascent movement development and maintain, while exacerbating the vertical cold and warm exchanges.

 (3) Water vapor mainly comes from the Bay of Bengal, the Caspian Sea and the Aral Sea, but the water vapor contribution from the Bay of Bengal is even greater.