利用NCEP 1°×1°再分析资料、宁夏区域自动站观测资料、FY-2E卫星资料，通过天气学诊断和数值模拟的方法对发生在贺兰山东麓的2018年7月18—19日和2017年6月4—5日两次伴随低空急流的暴雨过程进行对比分析。结果表明：（1） “7·18”过程是在500 hPa“东高西低”的环流背景下高空槽和偏南急流共同作用产生的局地短时暴雨，而“6·04”过程则是稳定大槽和东南急流影响下形成的大范围持续性降水过程。（2） 低空急流对两次暴雨过程的影响存在差异可能是急流分布形态不同所致，“7·18”过程暴雨发生前的低空偏南急流主要起到输送水汽的作用，当急流加强与贺兰山山体相互作用后诱发暴雨，且偏南急流偏转为西南急流，低空急流转向后与暴雨相互促进使降水加强；而“6·04”暴雨过程中宁夏北部地区一直处在中尺度低涡东南侧和东南急流左侧的有利动力条件下。（3） 数值敏感性试验的结果表明，减弱低空急流后，两次暴雨过程的降水强度均减弱，减小的区域分别位于贺兰山山区和宁夏平原中部地区，其中低空急流中的南风分量对降水的强度有重要影响。（4） 诊断分析结果显示，低空急流对“7·18”过程的影响主要体现在加强迎风坡垂直运动的动力作用，对“6·04”过程的影响则主要体现在急流左侧的动力辐合抬升作用，急流强度减弱对“7·18”过程水汽输送的影响较“6·04”过程更大。

Comparative analysis of two rainstorm processes was conducted using methods of synoptic diagnosis and numerical experiment with the NCEP 1°×1° reanalysis, and Ningxia regional automatic station observation, and FY-2E satellite data. These rainstorms occurred on the east side of the Helan Mountain from July 18 to 19, 2018 and June 4 to 5, 2017, which were all accompanied by low-level jet. (1) The “7·18” process is a short-term rainstorm, which is produced by the interaction of a high-altitude trough and southerly low-level jet under the circulation background of “high in the east and low in the west” at 500hPa, while the “6·04” process is a large-scale continuous precipitation process formed under the influence of the stable large-scale trough and the southeast low-level jet. (2) The difference in the impact of the low-level jet on the two rainstorms may be due to the different distribution patterns of the low-level jet. The low-level southerly jet before the “7·18” heavy rain mainly played the role of transporting water vapor. When the low-level jet strengthened and interacted with the Helan Mountains, the rainstorm was induced, and the southerly low-level jet was deflected into the southwest low-level jet. The low-level jet and the rainstorm process promoted each other to strengthen the precipitation. The northern part of Ningxia is always located on the southeast side of the mesoscale vortex and the left side of the southwest low-level jet during the “6·04” rainstorm. It is a favorable dynamic condition for the rainstorm. (3) Results of the numerical sensitivity experiment indicate that the precipitation intensity is weakened in the two rainstorms after decreasing intensity of the low-level jet; the reduced areas are located near the Helan Mountain and the central area of Ningxia plain, respectively. Among them, the south wind component of the low-level jet has an important impact on the precipitation intensity. (4) Results of diagnostic analyses show that the impacts of the low-level jet strengthen the dynamic effects of vertical movement at the windward slope for the “7·18” process, and the impact on the “6·04” process is mainly reflected in the dynamic convergence and uplift on the left side of the low-level jet. The influence of water vapor transport in the “7·18” process is greater than that in the “6·04” case.