A comparative analyses of the atmospheric circulation features associated with two extreme rainstorms on the northern slope of the Kunlun Mountains

Rainstorms on the northern slope of the Kunlun Mountains are of strong disaster-causing potential, posing significant challenges for refined forecasting and early warning. Therefore, gaining an in-depth understanding of the regional differences in their formation mechanisms is the key to improving rainstorm forecast accuracy. Using the data from meteorological observation stations in south Xinjiang, the fifth generation atmospheric reanalysis of the European Centre for Medium-Range Weather Forecasts, and the analysis data of the Global Data Assimilation System, this study comparatively analyzes the formation mechanisms of two extreme rainstorm events in the western section (case “5·18”) and the middle section (case “6·24”) of the northern slope of Kunlun Mountains. The results indicate that although the two rainstorms occurred under similar circulation backgrounds, they differed in the vertical structure of the influencing systems, water vapor transport, and the dynamic and thermodynamic coupling mechanisms. Prior to both rainstorms, the atmosphere was featured with high temperature and high humidity on the northern slope of the Kunlun Mountains. The geopotential height anomalies over the mid-high latitudes of Eurasia both displayed a “positive-negative-positive” distribution pattern. Additionally, the major influencing system at 500 hPa was the Central Asian low vortex in both cases. For case “5·18”, the South Asia high was in the Qinghai-Xizang high pattern, and the Central Asia low vortex exhibited a deep vertical structure, forming a stable synoptic situation of “combined actions from both east and west”. The joint effects of the pumping action of upper-level divergence, the mid-level baroclinic frontogenesis, and the low-level topographic forcing triggered a large-scale systematic ascending motion. Additionally, three airflows carrying water vapor and unstable energy were found to strongly converge at the western section of the northern slope of the Kunlun Mountains, subsequently triggering the “5·18” rainstorm. During this process, water vapor was transported primarily through northern and western paths from the ocean surface of Iceland and eastern Europe. For case “6·24”, the South Asia high was in a double-center pattern, while the Central Asia low vortex presented a shallow vertical structure. The combined effects of low-level shear convergence, topographic forcing, and mountain-valley thermal circulation jointly triggered the “6·24” rainstorm. In contrast, the dynamic conditions and energy release efficiency were both weaker than those in case “5·18”. Besides, local water vapor also played an important role in addition to the water vapor from the western and northern paths. The findings can deepen the understanding of the formation mechanisms of heavy rainfall in different regions on the northern slope of the Kunlun Mountains, thereby providing scientific support for refined forecasting, early warning, and disaster prevention and mitigation in this area.