Impacts of the 2019 Strong IOD and Monsoon Events on Indian Ocean Sea Surface Salinity

Abstract

The impact of the 2019 super positive Indian Ocean Dipole (PIOD) event, the strongest in the last four decades, which also cooccurred with an El Niño and a strong summer monsoon, on Indian Ocean sea surface salinity (SSS) is examined using the Soil Moisture Active Passive satellite measurements. Salt budget estimation suggests a predominant, nearly ocean-wide influence by surface freshwater flux and horizontal advective terms. Subsurface ocean influence on the salt budget occurs mainly in the southeastern tropical Indian Ocean (SETIO). The PIOD event suppressed the influence of the El Niño, thereby causing anomalous high precipitation in western India, and leading to an unusual freshening in the southeastern Arabian Sea (AS), which is subsequently advected towards the equatorial Indian Ocean (EIO). In the western Bay of Bengal (BoB), following the waning of monsoon-influenced precipitation in the fall, SSS becomes anomalously salty and traverses towards the AS against the flow of anomalous surface currents. During the peak of the summer monsoon in August-September and the peak of the PIOD event in September-November, SSS in the EIO exhibited tendency for freshening, mainly driven by westward advection of freshwater from the eastern BoB. Conversely, in the SETIO, there was tendency for salinification due to suppression of precipitation, enhanced upwelling of high subsurface salinity, and northward advection of salty water. During December to January of the following year, these salinity tendencies reversed, with salinification in the EIO and freshening in the SETIO.

Seasonal Variability of Sea Surface Salinity in the NW Gulf of Guinea from SMAP Satellite

“…Satellite measurements of SSS using 1.4 GHz L-band microwave sensors aboard the European Space Agency's Soil Moisture and Ocean Salinity (SMOS; launched November 2009), the US National Aeronautics and Space Administration (NASA)/Argentina Space Agency's Aquarius (June 2011 to June 2015), and the NASA Soil Moisture Active Passive (SMAP; launched January 2015) missions have fostered oceanographic and climate-related studies. Since its launch, SMAP data have been successfully evaluated and used in several oceanographic settings and found to reproduce, and in many instances, better characterize the surface salinity structure [e.g., Tang et al, 2017;Grodsky et al, 2019;Hackert et al, 2019;Menezes, 2020;Nyadjro 2021]. examined SMAP in the coastal waters of the Gulf of Maine and found the monthly SSS anomalies to be sufficiently accurate and applicable for coastal studies.…”