Near-surface circulation and kinetic energy in the tropical Indian Ocean derived from Lagrangian drifters

Trajectories of 412 satellite-tracked drifting buoys deployed in the tropical Indian Ocean have been analyzed to document the surface circulation and kinetic energy field. Only drifters drogued at 15 m depth and having drag area ratio greater than 35 are used to estimate current velocities. Unlike in earlier studies, the widening of the Equatorial Jet in the eastern equatorial Indian Ocean and the westward flow at the equator during July-August are apparent in the present data set. The comparison of drifter data with the seasonal mean dynamic topography (0/1000 db) shows that the surface circulation pattern inferred from dynamic topography does not always represent the surface currents in the Indian Ocean. Both compare well for the South Equatorial Current, the Equatorial Counter Current, and the southwestward current along the Indonesian Islands; they differ in the Bay of Bengal during the southwest monsoon, but are similar during the northeast monsoon. Maps of mean and eddy kinetic energy show maxima in the regions of western boundary currents and equatorial currents and minima in the Arabian Sea, the Bay of Bengal, and south of 20 degrees S.