The enhanced relationship between summer rainfall over the eastern Tibetan Plateau and sea surface temperature in the tropical southeastern Indian Ocean

Abstract

The summer rainfall in the eastern Tibetan Plateau (TP) is positively correlated with the sea surface temperature (SST) in the tropical southeastern Indian Ocean (SEIO). It is 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 more tropical moisture transported to the eastern TP (ETP) and the resultant above-normal-rainfall anomalies in the ETP in both the two epochs. However, the anomalous anticyclone and equatorial easterly anomalies associated with the warm SEIO SST anomalies is much stronger in P2 than those in P1. The warm SEIO SST anomalies are accompanied by a stronger El Niño in the preceding winter. It results in simultaneous warmer SST anomalies in the tropical Indian Ocean and colder SST anomalies in the equatorial central Pacific in P2. On the one hand, the excited meridional circulation induces suppressed convection leading to an anomalous anticyclone to the south of the TP. The anomalies of enhanced convection in the tropical eastern Indian Ocean and the downdrafts in the central Pacific favor the stronger equatorial easterly anomalies on the southern flank of anticyclone. On the other hand, the increased warming in the Indian Ocean basin produce an enhanced anticyclone and suppressed convection over the western North Pacific by emanating Kelvin waves. The diabatic cooling of suppressed convection induces the anomalous anticyclone to the south of the TP by exciting westward-propagating Rossby waves.