Enhanced Tropical Eastern Indian Ocean Rainfall Breaks down the Tropical Easterly Jet-Indian Rainfall Relationship

Abstract

AbstractPrevious studies found a tight connection between the tropical easterly jet (TEJ) and Indian summer monsoon rainfall (ISMR). Here we show that the TEJ-ISMR relationship is nonstationary and breaks down from 1994–2003 (epoch P2), in contrast to the significant positive correlation during the epoch P1 (1979–1993) and P3 (2004–2016). The breakdown of the TEJ-ISMR relationship concurs with the increased rainfall variability over the tropical eastern Indian Ocean (TEIO). The enhanced TEIO rainfall anomalies excite a significant lower-level cyclonic circulation that reduces the ISMR, meanwhile, strengthens the upper-level divergence and excites a pair of upper-level anticyclone to the west of the TEIO as Rossby wave responses, both accelerating the TEJ. Thus, the TEIO rainfall plays a more important role than the ISMR in the TEJ variability during P2, causing the breakdown of the TEJ-ISMR relationship. In contrast, a relatively weak amplitude of the TEIO rainfall during P1 and P3 was unable to change the positive TEJ-ISMR relationship. The changes in the TEIO rainfall variability is mainly attributed to the increased SST variability over the tropical southeastern Indian Ocean, but the cause of it remains elusive.