Sea surface salinity variability in the tropical Indian Ocean

Abstract

Argo profiles of temperature and salinity data from the north Indian Ocean have been used to address the seasonal and interannual variability of Sea Surface Salinity (SSS) and SSS Anomaly (SSSA) in 2 boxes from the eastern Equatorial Indian Ocean (EIO: 5°S–5°N, 90°–95°E) and Southeastern Arabian Sea (SEAS: 5°–9°N, 72°–76°E) and to compare with the HYbrid Coordinate Ocean Model (HYCOM) simulated SSS for the period from January 2002 to February 2007. The observational period covered one strong negative Indian Ocean Dipole Zonal Mode (IODZM) event in 2005 and a strong positive IODZM event in 2006. The Argo profiles in each box captured the impact of these IODZM events with a larger impact in the EIO box showing salting (positive SSSA, + 0.9) during negative IODZM (November 2005) and freshening (negative SSSA, − 0.6) during positive IODZM (November 2006). A band of positive (negative) SSSA occurs in the central EIO during negative (positive) IODZM event in 2005 (2006) under the influence of IODZM dynamics. The impact of IODZM event in the SEAS is more evident during boreal winter months. The observed anomalous eastward (westward) surface current contributed to the observed intense salting (freshening) during negative (positive) IODZM event in the EIO. Following the IODZM events, the East India Coastal Current (EICC) gets modulated through the propagation of downwelling/upwelling Kelvin Waves and further lead to the freshening/salting in the SEAS during boreal winter. These are well corroborated with the HYCOM simulations of SSS and currents. This study emphasizes that the HYCOM simulated salinity fields would be useful to provide rapid checks revealing either problems or successes in the satellite retrievals of salinity from the Soil Moisture and Ocean Salinity (SMOS) and Aquarius missions.