The Role of Salinity in the Southeastern Arabian Sea in Determining Monsoon Onset and Strength

Abstract

AbstractIn this study, we examine the role of freshwater transported from the Bay of Bengal into the southeastern Arabian Sea (SEAS) in determining both the timing of monsoon onset and the strength of the ensuing monsoon. To do this, we use a combination of satellite‐derived salinity data and reanalysis products from 1980 to 2016 in order to discuss seasonal, interannual, subdecadal, and long‐term decadal variability in various atmospheric and oceanic contributors such as ocean heat content, freshwater transport, ERA5 instantaneous moisture flux, mixed layer depth, and barrier layer thickness. The salt budget in the SEAS reveals the dominance of meridional freshwater advective transport that brings in variability in salinity and thus in salinity stratification, as well as in mixed layer processes. We find that these parameters exhibit the prevalence of a long‐term decadal variability (with trends of increasing/decreasing phases over a 15‐year duration) over which interannual (3‐year trend) and intradecadal (7‐year trend) variability trends are superimposed. The patterns of both the 3‐ and 7‐year trends follow each other closely, and relatively high amplitudes are seen in the 3‐year trends. The long‐term decrease in moisture flux and freshwater transport into the SEAS along with a rise in ocean heat content over a 15‐year duration after 1994 contributed to a lack of strong monsoons in recent years; the prevailing interannual and intradecadal variability in these parameters associated with the Indian Ocean Dipole and El Niño Southern Oscillation events favored weaker and normal monsoons after 1994.