Combined Effect of the Tropical Indian Ocean and Tropical North Atlantic Sea Surface Temperature Anomaly on the Tibetan Plateau Precipitation Anomaly in Late Summer

Precipitation variability over the Tibetan Plateau (TP) depends largely on the atmospheric circulation pattern associated with remote oceanic forcing, while the contribution of sea surface temperature anomaly (SSTA) in different ocean basins, especially the tropical North Atlantic (TNA), remains unclear. By using multi-source data and atmospheric general circulation model, this study reveals the individual and combined effects of the Indian Ocean Basin mode (IOBM) and TNA SSTA on the interannual variability of TP precipitation in late summer (August). During the positive phase of IOBM, warm SSTA in the Indian Ocean induces an anomalous anticyclone over the Bay of Bengal (BOBAC) via the Kelvin waveinduced Ekman divergence and the resultant positive precipitation anomaly over the southeastern TP. Simultaneously, an eastward-extending Kelvin wave triggered by the positive TNA SSTA overlaps with that caused by IOBM, further strengthening the BOBAC. In addition, the Kelvin wave triggered by TNA SSTA induces anomalous easterlies over the tropical Indo-Pacific, which contribute to the warm Indian Ocean SSTA and thus amplify the IOBM affecting TP precipitation. Moreover, the positive TNA SSTA generates a westward-extending Walker circulation anomaly that is responsible for the suppressed convection over the central Pacific, which in turn triggers a Rossby wave response and further strengthens the BOBAC. As a result, the positive precipitation anomaly over the southeastern TP is strengthened significantly. Particularly, considering the 23-month lead time of the IOBM and TNA SSTA, the tropical SSTA can be used as a predictor for the TP precipitation anomaly.