Sub-Surface Currents and High-Salinity Intrusions in the Southern Bay of Bengal during the Northeast Monsoon

Friday, 19 December 2014: 3:10 PM
Hemantha W Wijesekera1, Ewa Jarosz2, William J Teague1, Tommy G Jensen1, E. Joseph Metzger1, S.U.P. Jinadasa3, K Arulananthan3, Luca Centurioni4 and Harindra Fernando5, (1)Naval Research Laboratory, Stennis Space Center, MS, United States, (2)Naval Research Lab Stennis Space Center, Stennis Space Center, MS, United States, (3)National Aquatic Resources Research and Development Agenc, Colombo, Sri Lanka, (4)Scripps Institution of Oceanography, La Jolla, CA, United States, (5)University of Notre Dame,, Notre Dame, IN, United States
Shipboard velocity and CTD profiles collected in December 2013 from the R/V Roger Revelle along with satellite and drifter observations, and HYCOM nowcasts and COAMPS simulations show movement of sub-surface high-salinity intrusions into the Bay of Bengal (BoB) during the northeast monsoon. These observations were made as part of the Naval Research Laboratory research program titled “The Effects of Bay of Bengal Freshwater Flux on Indian Ocean Monsoon (EBOB)” and the Office of Naval Research (ONR) DRI titled “The Air-Sea Interaction in the Northern Indian Ocean (ASIRI)”. A major objective of ASIRI-EBOB program is to understand and to quantify dynamical processes and boundary transports that control fresh and salt water exchanges between the BoB and the Arabian Sea. The transects of currents collected from shipboard ADCPs in the southern BoB, southeast of Sri Lanka, along 5.25°N in December show a southeastward flowing, surface intensified boundary current (referred to as the East India Coastal Current (EICC)) in the upper 75 m with speeds as large as 1.6 m/s at 21 m depth. Outside the EICC, a sub-surface intensified, northward moving, 300 km wide current with strongest velocities as high as 1 m/s near 50-75 m depth was observed. The near surface currents derived from AVISO altimeter and drifter records show quantitatively similar flow patterns. Numerical models produce qualitatively similar flow fields. The combined observations and model results indicate that the EICC moves low-salinity water out of the BoB while the sub-surface current carries high-salinity water into the BoB.