Analysis of characteristics of mesoscale convective systems westward propagation process during summer in North China

In North China, the westward movement of summer mesoscale convective systems (MCS) is often accompanied by severe convective weather such as heavy rainfall, frequently causing significant meteorological disasters. To understand the basic characteristics of the westward-moving MCSs, the infrared brightness temperature data and the hourly combined precipitation products (COMB) were used to analyze the statistical characteristics of the westward-moving MCSs during the summer season from June to August during 2008-2018 in North China. The results are as follows. (1) The main moving direction of MCS during summer in North China is west-southwest. The frequency begins to increase significantly in the afternoon, peaks around 17:00-18:00 in the evening, and has the lowest occurrence probability at 8:00. (2) The westward-moving MCSs are classified into moderate-intensity precipitation and short-duration heavy precipitation according to precipitation intensity. A comparative analysis reveals that the active areas of short-duration heavy precipitation MCS processes are mainly concentrated in southern Hebei, northern Henan, and the central and western regions of Shandong; while the active areas of moderate-intensity precipitation MCS processes are relatively scattered. (3) The cloud-top brightness temperature of short-duration heavy precipitation MCS processes is relatively low, with a large cloud-top area and an average precipitation rate of 34 mm·h⁻¹. The areas with large cumulative precipitation are located in the steep windward slopes on the eastern side of the Taihang Mountains, the Taishan Mountains, and the transition zones between mountains and plains. The cloud-top brightness temperature of moderate-intensity precipitation processes is relatively high, with a small cloud-top area, and an average precipitation intensity is 8.7 mm·h⁻¹. The large-value center is located near the Lvliang Mountains in western North China, due to the relatively high frequency of MCS moving westward. This is a specialized study on westward-moving MCS, which serves as a valuable supplement to MCS theory and provides a theoretical reference for early warning, forecasting, and disaster prevention related to heavy rainfall in North China.