What Drives the Super Strong Precipitation over the Yangtze–Huaihe River Basin in the Meiyu Period of 2020?

During the Meiyu Period (June–July, JJ) of 2020, the Yangtze–Huaihe River basin (YHRB) in China experienced record-breaking rainfalls, resulting in severe floods and disasters. These rainfall anomalies were closely related to the extremely strong anomalous anticyclone developed over the western North Pacific (WNPAC), which favored convergence of water vapor over YHRB. The aim of this study is to determine the cause of the record-breaking rainfalls and WNPAC in the Meiyu period of 2020. It was found that a weak Central-Pacific El Niño rapidly decayed in spring and developed to a La Niña in late summer, whereas sea surface temperature (SST) in the tropical Indian Ocean (TIO) and tropical northern Atlantic (TNA) was considerably and persistently high from the previous winter to summer. The results showed that the weak decaying El Niño alone was insufficient to sustain the strong WNPAC in JJ of 2020, whereas the long-lasting warm SST anomalies in the TIO and TNA significantly contributed to the enhancement and westward shift of the WNPAC. The TIO warming intensifies the WNPAC by propagating Kelvin waves eastward and/or modulating the Hadley circulation. The TNA warming can force a westward-extending overturning circulation over the Pacific–Atlantic Oceans, with a sinking branch over the central tropical Pacific, which suppresses the convection activity over there and gives rise to the WNPAC. The TIO and TNA warming significantly contributed to the extremely strong WNPAC in JJ of 2020.