Upper Ocean Observations during DYNAMO in Central Indian Ocean

Three pairs of surface and subsurface moorings were deployed in the central Indian Ocean at equator, 1.5S, and 10S as a part of DYNAMO experiment to study the dynamics of MJO. Measurements of surface meteorology and upper ocean temperature, salinity, and velocity were taken between Sept 2011 and Jan 2012. An XBT survey between 12S and 2N along 79E quantified the meridional and vertical structures of temperature and identified the peak of Seychelles-Chagos thermocline ridge. Two EM-APEX floats took measurements of temperature, salinity, and velocity to as deep as 1500-m depth. Multiple layers of alternating meridional velocity with vertical scales of 50-200 m were observed, presumably associated with equatorial waves. Below the equatorial undercurrent, a strong westward current was observed showing a vertical structure distinctly different from that in the central Pacific Ocean. One EM-APEX float measured microstructure temperature variations and discovered similar vertical structure and magnitude of eddy diffusivity in the upper 150 m as found in the central equatorial Pacific below the equatorial cold tongue. Temperature, salinity, current, and shear within the surface mixed layer varied considerably with the local surface forcing. However, the local forcing could not explain the observed variations completely. Large scale atmospheric and oceanic forcing also played a significant role in modifying the oceanic surface mixed layer. Barrier layers were observed frequently in mooring measurements. Analyses were performed to understand the temperature, salinity, and momentum budgets in the central Indian Ocean.