Regional differences in hourly rainfall characteristics over the southeastern extension of the Tibetan Plateau

The southeastern extension of the Tibetan Plateau (SETP) is distributed by the typical longitudinal mountains and has unique climate characteristics and significant regional differences. The diurnal cycles of rainfall amount, frequency, and intensity over the SETP in the warm seasons (May-September) were investigated using high-density hourly station rainfall data and the possible mechanisms were discussed by analysing the ERA5 reanalysis and satellite data. The largest amounts of rainfall appeared on the southern and western margins of the SETP, and the rainfall amount was relatively small at the higher elevations of the SETP. Located at the southern margins of the SETP, the adjacent western (Reg_W) and eastern (Reg_E) regions presented a similar rainfall amount, frequency, and intensity, but the diurnal features of the two regions were quite different. The rainfall amount, frequency, and intensity had dominant peaks in the late afternoon in Reg_W, while in the early morning in Reg_E. A secondary peak in the early morning can be found in Reg_W. The diurnal features of the two regions were closely related with the low-level atmospheric conditions and the distribution of clouds. The enhanced convergence of the anomalous southerly winds and sufficient water vapour after midnight contributed to the nocturnal rainfall at the southern edge of the SETP. In the afternoon, the lower surface air temperature and more stable stratification in Reg_E, as compared with Reg_W, were relatively unfavourable for the occurrence of afternoon convection.