Spatio-temporal distribution of the rainstorm in the east side of the Helan Mountain and the possible causes of its variability

摘要

Compared with other arid areas, the convective rainstorm occurs more easily in the east side of the Helan Mountain, which is characterized by the short duration, large intensity, high precipitation efficiency and significant local distribution. In this paper, the 5-min and hourly precipitation at 512 regional automatic weather stations and other high-resolution observation data are used to analyze the spatio-temporal distribution and evolution characteristics of the rainstorm in the east side of the Helan Mountain during 2006 and 2019. Then, based on the daily precipitation data at 12 national observation stations, the rainstorm characteristics in this region during 1951 and 2005 are analyzed. On this basis, the rainstorm characteristics in the two periods are compared and studied. Finally, the possible causes of the distribution characteristics of rainstorm are initially discussed. The results show that the rainstorm with large magnitude and high intensity is mainly located in the mountainous region, and it mainly occurs in July with a high frequency period from afternoon to the first half of the night. Compared with 1951-2005, in 2006-2019 the rainstorm frequency, intensity and extremity are all increased, and the nocturnal and topographic features are more significant. The spatio-temporal distribution of rainstorm in the east side of the Helan Mountain is closely related to the nighttime enhancement of the low-level southeasterly jet and the interaction between the low-level jet and the mountainous topography. In the windward slope of the Helan Mountain, the interaction between the low-level jet and the mountainous topography could trigger or enhance the mesoand small-scale rainstorm systems, which would favor the occurrence of rainstorm. Overall, the conclusions in this study can deep the understanding of the rainstorms in the Helan Mountain, which could provide a reference for the monitoring and warning of rainstorms in this region.