Abstract
Previous 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 to 2003 (epoch P2), in contrast to the significant positive correlation during epochs P1 (1979–93) and P3 (2004–16). 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 and meanwhile strengthen the upper-level divergence and excite a pair of upper-level anticyclones 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 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 are mainly attributed to the increased SST variability over the tropical southeastern Indian Ocean, but their cause remains elusive.
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