Examining the salinity changes at different depths in the Indian Ocean prior to summer monsoon season and its connection to monsoon arrival in India :A case study

The Indian Ocean interacts intricately with the atmosphere, and its features, such as sea surface temperature and salinity.The Indian Ocean can influence the monsoon's onset, intensity, and duration.This study examines the fluctuation of the salinity in the Indian Ocean throughout the onset phase over the Indian Peninsula, with a focus on the Kerala coast.The study makes use of daily averaged reanalysis data from 1992 to 2017 from the Ocean Reanalysis System 5 (ORAS) of the European Centre for Medium-Range Weather Forecasts (ECMWF).Considerable variations in salinity have been seen in the Indian Ocean prior to the onset of the monsoon.Higher salinity levels are found in the top subsurface layers of the western Indian Ocean, namely the Arabian Sea, whereas lower salinity concentrations are found in the equivalent layers of the eastern Indian Ocean, which include the Bay of Bengal.The salinity gradient between the Arabian Sea and Bay of Bengal decreases with depth due to the inflow of freshwater into Bay of Bengal through river discharge.The peak salinity is localized in a specific region, adjacent to the Somalia and Kenya coastlines, within depths ranging from 20 to 80 meters from March to the first week of May.Subsequently, this region of heightened salinity, extends to depths ranging from 50 to 90 meters.During the pre-monsoon months of the early onset year, intense evaporation leads to immense moisture in the atmosphere.Conversely, moisture is low during normal onset and late onset years, with wind-driven moisture transport towards the Kerala coast.