Moored Current Observations in the Southern Bay of Bengal

Deep moorings were deployed in the southern Bay of Bengal by the Naval Research Laboratory as part of the EBOB (Effects of Bay of Bengal Freshwater Flux on Indian Ocean Monsoon) program in an effort facilitated by the Office of Naval Research and also part of the international research program , ASIRI (Air-Sea Interactions in the Northern Indian Ocean; (2013-2017). Six moorings were deployed in December 2013 and recovered in August 2015. Each mooring contained two acoustic Doppler current profilers (ADCPs), an upward –looking 300 kHz ADCP and a downward-looking 75 kHz ADCP, mounted on a flotation ball (at depths ranging from 20 to 75m) which provided current velocity profiles for the upper 500 m of the water column, at water depths of about 3800 m. Additionally, seventeen to nineteen sensors, measuring temperature, salinity, and pressure, were mounted over an interval of about 400m below the ADCPs. Wavelet analyses show significant peaks at periods of about 12 h, 5 d, 40 d, 70 d, and 320 d. The peak at about 12 h is tidal. The 5 d peak is likely related to inertial or atmospheric activity. Large near-surface currents (6 m) in excess of 140 cm/s were observed and were consistent with southwest monsoon winds of 10 to 15 m/s. Currents exceeding 50 cm/s were found down to depths of 80 m. Currents greater than 20 cm/s were common at depths of 450 m. High salinity inflow was observed during the summer monsoon periods. The observed current magnitudes in the interior of the southern Bay of Bengal were similar in magnitude to boundary currents observed near Sri Lanka.