Dynamics and forcing mechanisms of upwelling along the south eastern Arabian sea during south west monsoon

Abstract

The study was carried out to understand the upwelling and its forcing mechanisms along South Eastern Arabian Sea (SEAS) during the southwest monsoon. Ship observations onboard FORV Sagar Sampada during summer monsoon (August 2017) and satellite data during the period were used to delineate these mechanisms. Here, sea level anomaly (SLA), Ekman transport, Ekman pumping velocity and Brunt–Vaisala frequency are considered as indices as well as proxies for upwelling. Also, the zonal and meridional variations of hydrographic parameters along the SEAS during summer monsoon are studied in detail using in situ observations. Coastal variations showed maximum upwelling intensity off Cape whereas offshore variation showed maximum intensity off Kochi leading to maximum offshore Ekman transport. These variations are investigated by studying the differences in D26, D24 isotherms and local temperature anomaly. The alongshore component of wind is observed to be strong from southern transects extending from Trivandrum to Mangalore where the upwelling signals are dominant. Intense upwelling off Cape is observed to be due to cross-shore component of wind. Ekman transport due to cross-shore component of wind during the period is observed to be maximum at 6–8oN and decreases towards north but eventually increases on reaching to Goa. Ekman transport due to alongshore component of wind and pumping velocity are maximum at 8–10oN when compared to southern region (6–8oN) and also reduces further north (10–15.2oN). The offshore Ekman transport, pumping velocity, sea level anomaly and mixing of watermasses play a major role in the variation of upwelling intensities in the SEAS.