贺兰山东麓20次暴雨过程环流形势及低空急流特征. (Chinese)

The eastern region of the Helan Mountain is an area prone to extreme rainstorms in Northwest China. To further explore the distribution of circulation patterns and evolution characteristics of the low-level jet systems during a rainstorm occurrence in this region and improve the accuracy of rainstorm forecasts and the ability of disaster prevention and mitigation in this region. Based on the encrypted surface precipitation observation and NCEP/NCAR reanalysis data, this paper comprehensively analyzed the formation mechanism of 20 heavy rainfall events in the eastern piedmont of the Helan Mountain from 2009 to 2020. The results show that: According to the characteristics of the 500 hPa circulation situation, the main rainstorm processes in this area can be classified into two: “Northwest side of the subtropical high ”and “In front of upper trough ”category rainstorm. The rainstorm of “In front of upper trough” category occurs under the combined action of the highaltitude westerly trough, the high-altitude jet stream, and the low-altitude water vapor convergence field. During the precipitation process on the northwest side of the subtropical high, the eastern foot of Helan Mountain is located on the northwest side of the western Pacific subtropical high. The edge of the subtropical high brings abundant water vapor, and the combination of high and low- altitude dynamics strengthens this type of precipitation. Obvious differences exist in the LLJ systems corresponding to the two types of precipitation processes. During the precipitation process of the “Northwest side of the subtropical high” category, the LLJ shows the characteristics of northward intensification and southward retreat and weakening. The LLJ axis is mainly located on the left side of the Helan Mountains. Its main effect on such rainstorm process is reflected in the transport of water vapor and the increased wind speed on the windward slope. “In front of upper trough” category rainstorm’s LLJ is characterized by eastward movement and weakening, and the jet axis is mostly located on the right side of the Helan Mountains. The development and evolution of mesoscale cyclones generated by LLJ dynamics play an important role in triggering and maintaining such rainstorms. [ABSTRACT FROM AUTHOR]

贺兰山东麓是中国西北极端暴雨易发区之一, 为了进一步探究该地区暴雨发生时大气环流配置及低空急 流系统演变特征, 提高该地区暴雨预报准确率及防灾减灾能力, 本文利用加密地面降水观测资料和NCEP/NCAR再 分析资料, 对2009—2020年贺兰山东麓20次暴雨事件的形成机理进行了综合分析。结果表明: (1) 依据500 hPa环 流形势特征可将该地区20次暴雨过程分为高空槽前型和西太平洋副热带高压西北侧型。高空槽前型降水是在高 空西风槽影响下, 配合高空急流及低空水汽辐合场发生与维持, 副高西北侧型降水过程中贺兰山东麓位于西太平 洋副热带高压西北侧, 副高边缘带来充沛水汽, 高低空动力辐合配合使得该类降水强度更强。（2) 两类降水过程对 应的低空急流系统存在明显差异, 副高西北侧型降水其低空急流呈北进增强-南退减弱特点, 急流轴在贺兰山体左 侧, 在暴雨过程中起到了水汽输送及增大迎风坡风速等作用。（3) 高空槽前型降水过程中低空急流多呈东移减弱特 点, 急流轴位于山体右侧, 低空急流动力作用所产生的中尺度气旋的发展演变对此类暴雨的触发与维持起到重要 作用。 [ABSTRACT FROM AUTHOR]

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