Monsoon currents and fresh- and salt-water pathways in the Southern Bay of Bengal

Hydrographic and velocity observations were measured from ships, drifters, and moored platforms in the southern Bay of Bengal and around Sri Lanka as part of the international research program (2013-2017), ASIRI (Air-Sea Interactions in the Northern Indian Ocean). Here shipboard velocity and hydrographic profiles collected in December 2013 and August 2015 along with drifter observations, satellite altimetry, global ocean nowcast/forecast products, and coupled model simulations were used to examine the circulation in the southern Bay of Bengal. The observations captured the southward flowing East India Coastal Current (EICC) off southeast India and east Sri Lanka, northward flow east of the EICC during the NE monsoon, and the northeastward moving Southwest Monsoon Current (SMC), southeast of Sri Lanka, during the SW monsoon. The EICC, the northward flow east of the EICC, and the SMC were as large as 1 m s^-1 in the upper 75-125 m. The EICC moved low-salinity water out of the bay, while the subsurface intensified northward flows found during NE and SW monsoons carried high salinity water into the bay. The observations are consistent with northward high-salinity subsurface flow in numerical model solutions.