Surface circulation off Somalia and western equatorial Indian Ocean during summer monsoon of 1988 from Geosat altimeter data

Abstract

The sea level variability derived from repeating tracks of the Geosat altimeter data during the late phase (August-September) of the summer monsoon of 1988 revealed the presence of multiple meso-scale eddy features with clockwise and anti-clockwise rotation. During August, the prime eddy or the Great Whirl centred at 9·5° N, 53·5° E off northern Somalia and the southern gyre centred at 3°N, 51·5° E off southern Somalia, both are clearly identified with clockwise rotation. The region of lower sea levels off the central Somalia coast (between 6°N and 9°N) coincides with the cold water wedge formed by the offshore movement of the cold upwelled waters from the Somalia coast during the summer monsoon. By September the southern gyre weakens, while the prime eddy persists. The surface circulation is characterized by nearly meridional flows in the equatorial region. A strong narrow (~ 100 km) southward jet-like flow is noticed south of 7° N between 53° and 54° E during September. In general, these circulation features are in agreement with the sea surface topography derived from the hydrographic data collected in this region during the same period on board the ORV Sagar Kanya.