Radar Observations of Summer Mesoscale Convective Systems Over the Eastern Tibetan Plateau and Sichuan Basin in Southwest China

Abstract This work studies the characteristics of mesoscale convective systems (MCSs) over the eastern Tibetan Plateau (ETP) and Sichuan Basin (SB), Southwest China using radar observations in summer of 2016–2020, and their ambient conditions using the ERA5 reanalysis. A total of 171 MCSs are identified, with 76% generated in the SB while the others in the mountainous region above 1,500 m. Basin MCSs mainly occur in the western and southeastern SB, peaking at 00–02 Beijing Time (BJT). By contrast, mountain MCSs primarily form over the western Sichuan plateau and the ETP's eastern steep slope, peaking at 20–22 BJT. This diurnal difference is attributed to the reversal of the thermally‐driven circulation between the ETP and SB in the afternoon and night. Compared to mountain MCSs, basin MCSs develop in an environment of higher most unstable convective available potential energy, with stronger vertical wind shear and dewpoint depression between 0 and 3 km above ground. Thus, basin MCSs tend to be longer–lived and larger in area than their mountain counterparts, with a shorter upscale growth time from first echo. Basin MCSs are dominated by linear convective modes (63.8%), especially in the organization modes of trailing stratiform and leading stratiform, which are of higher hourly precipitation intensity than non–linear (NL) mode. Contrastingly, in the mountainous region, there are predominantly more NL MCSs (58.5%) which have higher hourly precipitation intensity than linear ones on average, likely due to greater topographic lifting and blocking.