Statistical Features of Two Types of Mesoscale Convective Systems (MCSs) Generated over the Eastern Tibetan Plateau during 16 Consecutive Warm Seasons

Two types of mesoscale convective systems (MCSs) generated over the eastern Tibetan Plateau (TP) during 16 consecutive warm seasons were identified and tracked by an automatic tracking algorithm based on hourly geostationary satellite TBB data that were provided by Kochi University. Following the manual verification of the automatic tracking results, statistical and comparative analyses of these two types of MCSs were conducted using NOAA’s CMORPH (Climate Prediction Center Morphing) precipitation data and NCEP’s CFSR (Climate Forecast System Reanalysis) reanalysis data. The main results show that July and August were the most active months regarding the MCSs’ generation over the eastern section of the plateau, but the percentages of MCSs’ vacating the TP of these two months were the lowest. In May, the number of MCSs generated reached a minimum, but up to nearly 40% of the MCSs could vacate the TP. The MCSs that could vacate the TP (V-MCS) usually showed a longer lifespan, earlier triggering time, and lower proportion of short lifespan cases, compared with the MCSs that could not vacate the TP (N-MCS). During the period of the research, the V-MCSs were usually faster in development and stronger in intensity, compared with the N-MCSs. However, owing to the much lower frequency in the occurrence of V-MCSs, their contribution to the local precipitation was only about 15%, which was approximately half the contribution of the N-MCSs. The composite circulation features of the V-MCSs and N-MCSs that were generated over the eastern plateau were significantly different. The shortwave trough and stronger westerly wind in the middle troposphere and the cyclonic wind shear in the lower troposphere provided more favorable conditions for the V-MCSs’ occurrence, maintenance, and eastward displacement. In contrast, divergence conditions in the upper troposphere were more conducive to the N-MCSs (the associated South Asia high in this type was stronger).