The enhanced relationship between summer rainfall over the eastern Tibetan Plateau and sea surface temperature in the tropical Indo-Pacific Ocean

Previous studies reported that summer rainfall in the eastern Tibetan Plateau (TP) is affected by the sea surface temperature (SST) in the tropical southeastern Indian Ocean (SEIO). In this study, we found that their relationship has enhanced significantly during the second period of 1984–2015 (P2) compared to the first period of 1951–1983 (P1). The anomalous anticyclone to the south of the TP is the major factor favoring ocean moisture transported to the eastern TP (ETP) and resultant local above-normal rainfall anomalies. However, the anomalous anticyclone is only significantly correlated with warm SEIO SST anomalies in P2. Further studies of possible reasons show that warm summer SEIO SST anomalies are accompanied by a stronger typical El Niño in the preceding winter of P2. It results in warmer SST anomalies in the tropical Indian Ocean, including the SEIO, and colder SST anomalies in the central Pacific in summer of P2. On the one hand, the increased warming in the whole tropical Indian Ocean emanates Kelvin waves to trigger stronger suppressed convection over the western North Pacific. It induces the anomalous anticyclone to the south of the TP by exciting westward-propagating Rossby waves in P2. On the other hand, the tropical warmer SEIO and colder Pacific SST anomalies produce anomalous Walker cells, triggering stronger equatorial easterly anomalies. The equatorial easterly anomalies and suppressed convection to the south of the TP also induced by warmer SEIO SST through meridional circulation jointly contribute to formation of the significant local anomalous anticyclone in P2.