Abstract:Using hourly precipitation data, conventional meteorological observations, Yinchuan CA Radar data and ERA5 high resolution reanalysis data from 2006 to 2021, this paper studies the temporal and spatial correlations between the low-level jet and the rainstorm process in the eastern region of the Helan Mountains, and discusses initially the possible impact mechanism for low-level jets to affect the occurrence and development of rainstorm. The results show that the low-level jets that influence the rainstorms in the eastern foot of the Helan Mountains are mainly distributed in three key areas, i.e., the southern Hetao Region, southeastern Ningxia Hui Autonomons Region and southwestern Shanxi Province, corresponding to southerly jet at 700 hPa, southern jet at 775 hPa and southeastern jet at 850 hPa, respectively. The southeast of Ningxia is a key transfer zone where three low-level jets merge before their continuously developing towards north and west, and has much more prominent impact on the occurrence and development of the rainstorm process in the eastern region of Helan Mountains. According to the height of the maximum wind speed axis of the low-level jet, the low-level jet processes affecting the rainstorm processes in the eastern region of Helan Mountains are divided into seven types. Among them, the frequency of the three levels jet pattern is the highest, accounting for about 54.5% of the total processes, followed by the processes during which the jet streams at 700 hPa and 775 hPa occur simultaneously (36.5%). The occurrence of rainstorm processes is consistent with the low-level jets in time. To be illustrated, the onsets of low-level jets at 700, 775 and 850 hPa are 18, 10 and 7 hours earlier on average than the beginning of rainstorms. The maximum wind speeds of low-level jets at 700 hPa and 775 hPa jet stream are 54 min and 18 min earlier than the appearance of the maximum rainfall intensities of rainstorm process, while the maximum wind speed of low-level jet at 850 hPa lags 12 min on average behind the occurrence of maximum intensity of rainstorm process. The frequencies of 850 hPa Level-Ⅰ jet and 775 hPa Level-Ⅱ jet are more indicative of the frequency of short-term rainstorm of 20-40 mm·h-1 and 40-60 mm·h-1 respectively, whereas the average wind speed of low-level jet at 700 hPa in the key area in the south of Hetao is more indicative of the maximum rainfall intensity of the rainstorm process. In addition, there exists also spatial consistency between rainstorm process and low-level jet, that is, as the low-level jet builds, strengthens and moves towards north or west, or weakens and retreats eastward or southward, the rainstorm starts, intensifies and weakens, and the location of rainstorm is found in the left front of the jet axis. With the effect of the topography of Helan Mountains, the low-level jet moves northward and westward, triggering multiple convective cells in front of the east slope of the mountain, merging and strengthening to form a linear echo with slow movement, strong development, highly organized and obvious train effect, thus very prone to cause the localized severe convective rainstorms to occur in the Helan Mountains Region.