SST‐forced interdecadal deepening of the winter India‐Burma trough since the 1950s

Abstract

AbstractThe winter India‐Burma Trough (IBT) has undergone a pronounced interdecadal deepening since the 1950s, which led to the significant rainfall increasing over the eastern Indochina Peninsula and south China. To better understand such an observed IBT change, this study examines the responses of the IBT to the upstream subtropical jet, historical anthropogenic forcing, and tropical sea surface temperature (SST). Results show that the SST warming that occurs in the eastern tropical Indian Ocean (ETIO) is the primary cause of the observed interdecadal IBT deepening. The remarkable SST warming leads to a reduction of sea level pressure (SLP) over ETIO by diabatic heating. In association with the change of zonal SLP gradient, the westerly wind anomalies are observed. The northern flank of the westerlies further induces a cyclonic Rossby wave response over the Bay of Bengal. As a result, the winter IBT is intensified. This attribution can be supported by the simulations of atmosphere general circulation models forced by historical SST, in which the observed IBT changes are well simulated on both interdecadal and interannual time scales.