Based on the observational hourly precipitation data and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis 5 (ERA5) products from 2006 to 2020, 22 rainstorm processes in the eastern foot of Helan Mountain are objectively classified by using the hierarchical clustering method, and the circulation characteristics of different patterns are comparatively analyzed in this study. The results show that the occurrences of rainstorm processes in the eastern foot of Helan Mountain are most closely related to three circulation patterns. Patterns I and Ⅲ mainly occur in July and August, with similar zonal circulations in synoptic backgrounds. Specifically, the South Asia high and the western Pacific subtropical high are stronger and more northward than those in normal years. The frontal systems in westerlies are inactive, while the water vapor from the ocean surface in the south is mainly transported to the rainstorm area by the southerly jet stream at 700 hPa. The dynamic lifting anomalies are relatively weak, the instability of atmospheric stratification is anomalously strong, and thus the localized severe convective rainstorm is more significant. Comparatively, rainstorm processes of pattern I are accompanied by stronger and deeper ascending motions, and the warm-sector rainstorm is more extreme. Pattern Ⅲ shows a stronger and deeper convective instability, accompanied by larger low-level moisture. Rainstorm processes of pattern Ⅱ mainly occur in early summer and early autumn, presenting a meridional circulation pattern of high in the east and low in the west in terms of geopotential height. Moreover, the two low-level jets transporting the water vapor northward from the ocean on the east of China encounter with the frontal systems in westerlies, which makes the ascending motion in pattern Ⅱ anomalously strong and deep. The relatively weak instability of atmospheric stratification causes weak convection and long-lasting precipitation formed by the confluence of cold air and warm air. This study may help improve rainstorm forecasting in arid regions.

CHEN Yu-ying;LI Jian-ping;ZHANG Su-zhao;SU Yang;YANG Yin;ZHANG Yi-xing;YAO Shan-shan

Key Laboratory for Meteorological Disaster Monitoring and Early Warning and Risk Management of Characteristic Agriculture in Arid Regions,CMA,Yinchuan 750002 China;Ningxia Key Laboratory of Meteorological Disaster Prevention and Mitigation,Yinchuan 750002 China;Ningxia Meteorological Observatory,Yinchuan 750002 China;Key Laboratory of Physical Oceanography,Institute for Advanced Ocean Studies, Qingdao National Laboratory for Marine Science and Technology,Ocean University of China, Qingdao,Shandong 266100 China

热带气象学报（英文版）

[1]CHEN Yu-ying;LI Jian-ping;ZHANG Su-zhao;SU Yang;YANG Yin;ZHANG Yi-xing;YAO Shan-shan-.Circulations and Thermodynamic Characteristics of Different Patterns of Rainstorm Processes in the Eastern Foot of Helan Mountain)[J].热带气象学报（英文版）,2022(03):343-363

Circulations,Rainstorm,Helan

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