The Role of Salinity in Determining Southwest Monsoon Variability

Freshwater transport from the Bay of Bengal into the southeastern Arabian Sea (SEAS) creates a barrier layer and allows for the development of the Arabian Sea Mini Warm Pool (ASMWP), which in turn allows for the genesis of a monsoon onset vortex prior to the onset of southwest monsoon. This research examines how this freshwater transport influences the strength and timing of the southwest monsoon using a combination of satellite-derived salinity and reanalysis from 1980 to 2016. We examine a variety of ocean and atmospheric parameters, such as ocean heat content (OHC), freshwater transport, moisture flux, and barrier layer thickness (BLT) to find sub-decadal and decadal variability in the SEAS region to discuss the lack of strong monsoons since 1994. We find strong 3-year, 7-year, and 15-year trends indicative of interannual and longer-term variability associated with the El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and global climate change. The long-term decrease in moisture flux and freshwater transport both coincide with an increase in OHC since 1994, which appears to contribute to lack of strong monsoons in recent years. This prevailing interdecadal variability in OHC, BLT, freshwater transport, and moisture flux, along with ENSO and IOD phases, has contributed to the increased number of weak monsoons in recent years. We find that the interplay of air-sea coupled processes in the SEAS on sub-decadal and interdecadal timescales resulted in the observed trends in southwest monsoon strength and that these processes will become increasingly important as the global climate continues to change.