Recurrence of wintertime SST anomalies in the Bay of Bengal: characteristics and causes

摘要

This study investigates the winter-to-winter recurrence (WWR) of sea surface temperature anomaly (SSTA) in the Bay of Bengal (BOB) and its causes. During 1948-2016, 36% years show WWRs, which occurred over the BOB north of 13 degrees N. The WWR of net surface heat flux (Qnet), especially the latent heat flux (Qlat) associated with change of winter monsoon wind speed, is essential for all the SSTA WWR events. The interdecadal wintertime warming (cooling) of BOB SST before (after) 1976, which is induced by the weakened (enhanced) monsoon wind and latent heat flux associated with the Interdecadal Pacific Oscillation (IPO) and decadal variability of the Indian Ocean, are the causes for the observed interdecadal variability of warm (cold) SSTA WWR. However, nearly half (48%) of the WWR events are significantly contributed from the subsurface processes, which is equivalent to similar to 26% (42%) contribution to Qnet for the warm (cold) SSTA WWR events. Different from the mid-latitude subsurface re-emergence mechanism that depends critically on wintertime mixed layer deepening, the BOB subsurface effects on WWR of SSTA are associated with shoaling/deepening thermocline, forced remotely by winds along the equator and Ekman pumping within the BOB.