Abstract: In spring, persist rainfall often occurs in East China. Accounting for more than 30% of annual precipitation, spring persist rainfall (SPR) significantly affects the hydrological cycle and water supplies for agriculture in the climate system via cloud-radiation feedbacks. Previous studies suggested that the Tibetan Plateau (TP) is the direct climatic cause of SPR. However, SPR and associated cloud radiative effects are not well simulated in the state-of-the-art reanalysis datasets and climate models that precipitate the CMIP6 project. Based on a series of 27-km regional climate simulations using the Weather Research and Forecasting (WRF) model, this work studies the impacts of subgrid-scale orographic drag (SOD) over the TP on the SPR. Results show that, in the absence of TP_SOD, the deflected southwesterly flow on the south flank of the TP is too weak, with insufficient water vapor transported from the Bay of Bengal (BOB) to the SEC. Moreover, the western Pacific subtropical high (WPSH) is too strong and extends to far westwards, which greatly suppresses the vertical lifting in the SEC. As a result, the SPR is severely underestimated by more than 40% as compared to the CMORPH precipitation observation. In contrast, the SPR is in very good agreement with the observation when the SOD over the TP is taken into account. The westward SOD over the TP can induce a meridional circulation across the TP. Due to this “orographic drag dynamic pumping”, the pressure field lowers along the southern flank of the TP, leading to an increase of meridional pressure gradient and thus acceleration of the deflected southwesterly flow.
 

Tibetan Plateau,Spring Rainfall,gravity wave