Warm season nocturnal rainfall over the eastern periphery of the Tibetan Plateau and its relationship with rainfall events in adjacent regions

摘要

Hourly observational records are used to investigate the distinct nocturnal rainfall and related convection activities over the eastern periphery of the Tibetan Plateau (EPTP). The results show that rainfall events over the EPTP are characterized by frequent moderate rainfall with long durations, which differs from both the eastern Tibetan Plateau (TP_E) and the west Sichuan Basin (SCB_W). Although the nocturnal rainfall dominates the warm season rainfall over the EPTP and its adjacent slopes, the midnight rainfall peak is more evident over the slope and basin regions, whereas over the TP_E, the rainfall intensity tends to peak in the late afternoon. An eastwards phase delay is found from the TP_E to the downstream EPTP regions, and the signal is more evident in the intense long-duration rainfall events. To demonstrate the regional characteristics of the rainfall processes over the EPTP and its adjacent areas, a regional rainfall event (RRE) method is applied to consider the spatiotemporal evolution of the rainfall processes. The intense long-duration RREs over the EPTP are selected and classified into two categories, with one related to the early stage rainfall systems in the TP region (RRE_with_TP) and the other not related to the TP rainfall systems (RRE_without_TP). The RRE_with_TP cases are probably related to the propagation of rainfall systems from the plateau. By analysing the convective activity derived from the FY-2 geostationary satellites, evidence of the close relationship between the RRE_with_TP cases and the eastwards propagation of the convective systems that develop over the TP in the late afternoon is shown, whereas the RRE_without_TP cases seem to be more locally initialized or caused by rainfall systems from eastern regions. These results provide more detailed metrics to evaluate model performances over the EPTP region where excessive rainfall has been a long-standing problem in the simulation of the East Asian climate.