Spatiotemporal Distribution Characteristics of MCSs Producing Short-Duration Heavy Rainfall over the Tianshan Mountain Area

Based on hourly precipitation data and FY-2 satellite infrared (IR) digital satellite imagery collected during the warm season from 2005 to 2015 in the Tianshan Mountains and the adjacent areas in Xinjiang, China, the definition of mesoscale convective systems (MCSs) was revised based on short-duration heavy precipitation processes. The spatiotemporal development of MCSs in terms of the initiation, maturation, dissipation, duration and movement was statistically analyzed. Most mesoscale systems in the area were dominated by meso-β convective systems (MβCSs), which was in line with the annual heavy precipitation frequency. In meso-α convective systems (MαCSs), persistent elongated convective systems (PECS) occurred more commonly than mesoscale convective complexes (MCCs). MCSs were common in summer, with the peak frequency of MαCS occurrence in June and the peak frequency of MβCS occurrence mainly in July and August. From the perspective of diurnal variations, MCSs initiated in the late afternoon, developed during the evening, and dissipated before midnight. MCSs in general lasted 6~9 h between June and July and 9~11 h in August. The MαCSs lasted approximately 14 h, and the MβCSs lasted from 7 h to 12 h. The development and termination stages of MCSs lasted 3~6 h and 2~7 h, respectively. In low-elevation areas and on the windward slope of the mountains, MCSs initiated more easily and more frequently over the northern and western slopes than over the southern and eastern slopes. The central area of the Junggar basin hosted the development of MCSs, but the distribution of the convective systems at different scales varied. During the termination stage, these mesoscale systems were mainly located at the basin edges. In terms of tracks, most MCSs moved eastward under the influence of the westerlies, and the MαCSs moved faster but in a more scattered manner than the MβCSs. Additionally, some unusual tracks appeared because of the effects of the underlying surface topography and environmental wind.