Surface currents in the area of the Indo-Pacific throughflow and in the tropical Indian Ocean observed with surface drifters


  • Yutaka Michida,

  • Hiroyuki Yoritaka


The location data set of 31 surface drifters deployed in the Indian Ocean between 1990 and 1993 are analyzed to illustrate the surface current field and its seasonal changes in the tropical Indian Ocean and the area of Indo-Pacific throughflow. Trajectories of drifters, daily drifting velocities, and grid-averaged velocities are described and compared with published climatologies of the surface currents in the Indian Ocean and numerically simulated flows in the Indonesian Seas. The surface current field and its seasonal changes in the Indian Ocean derived from drifter data are generally consistent with the published climatologies. Zonal velocities computed from the drifter data set in the equatorial jet, which appears twice a year in the transition periods of the monsoon, are greater than previous estimations. Surface currents flowing from the Indian Ocean toward the Indonesian Seas in boreal winter, in the opposite direction from that observed during other seasons, are traced with drifters deployed in the region south of the Indonesian archipelago. In particular, a drifter passing from the Indian Ocean to the Flores Sea through Lombok Strait in December 1993 is consistent with numerical modeling which shows northward flow in the Lombok Strait in boreal winter.