Imprints of Compound Height Heat Extremes in the Northern Bay of Bengal

Abstract

Marine heat waves (MHW) are extreme warming events, and height extreme events (HEXs) are extreme increases in the sea surface height in the ocean. These two extreme events have substantial consequences on their own. This study explores the causes and effects of compound height heat extremes (CHHEX), which involve the co-occurrence of MHW and HEX events over the northern Bay of Bengal (BOB) from 1993 to 2020. In order to understand the behaviour of these extreme events, composite analysis is performed using various reanalysis and satellite products. Low atmospheric heating days were observed during the HEX events. The observed high ocean surface warming during HEX events is due to the effects of local winds and remote forcing. The combined effect of net heat flux, local winds, and remote forcing leads to the warming of the northern BoB during CHHEX events. A case study analysis is done for the 2015 CHHEX event to understand the role of remote forcing. The observation indicates that downwelling Rossby waves travelling westward are responsible for the abnormal warming during that period. The study also found a high correlation between sea surface temperature anomaly (SSTA) and sea level anomaly (SLA) during the CHHEXs MHWs and HEX events.