Anomalous sea surface temperature over the Southeastern Arabian Sea during contrasting Indian Ocean Dipole years

Signatures of Indian Ocean Dipole (IOD) over the southeastern Arabian Sea (SEAS) during two representative IOD years: negative IOD 2016 (nIOD16) and positive IOD 2019 (pIOD19) are studied. Sea Surface Temperature (SST) over the SEAS reveals negative anomalies during the Fall transition months of nIOD16, whereas positive SST anomalies are observed during both southwest monsoon season and Fall transition months in pIOD19. In contrast, during the first half of the year, noticeable positive SST anomalies are observed in nIOD16, whereas SST anomalies are weak in pIOD19. The cooling rate during the SWM season of nIOD16 was twice that during pIOD19 and lasted one additional month. To understand the aforementioned anomalous features in the SST evolution, a heat budget analysis is performed based on a combination of in-situ data, satellite measurements and ocean reanalysis. The enhanced cooling during the SWM season of nIOD16 was driven largely by the net heat flux. In addition, the penetrative component of shortwave radiation also favoured enhanced cooling during both the SWM season and Fall transition months of nIOD16, driven by a relatively small mixed layer depth (MLD). The negative anomaly in MLD during the SWM and Fall transition months of nIOD16 is then shown to be in line with corresponding positive anomalies in the Ekman pumping. In contrast, relatively less intense cooling during the SWM season of pIOD19 is attributed to small resultant net heat flux and warming by the residual term.