SAR observations of organized large eddies over the Somali current

Abstract

The Arabian Sea is characterized by an annually reversing circulation influenced by strong monsoon winds. The southwest monsoon that occurs during summer drives a northward boundary current along the coast of Somalia. During the winter monsoon, the southward flowing Somali Current merges with the northward flowing East African Coastal Current to form the eastward flowing South Equatorial Counter Current. This pattern shifts during the summer monsoon as the East African Coastal Current feeds the reversing Somali Current. Part of this northward flow retroflects from the coast at about 4°N to form the Southern Gyre while the remaining flow continues north past the Gulf of Aden or detaches at about 10°N to form the Great Whirl. Sentinel-1 synthetic aperture radar (SAR) data were acquired over the Somali Current in 2016 during the summer and winter monsoons. The Somali Current along the coast, the Southern Gyre and the Great Whirl are well developed at the time of the summer acquisition. The covariability of the atmospheric boundary layer and sea surface temperature was observed at high resolution over the Western Arabian Sea. Wind stress curl derived from the SAR data show the effects of the cold upwelled water and the Somali Current on the wind speed. Significant organized large eddies (OLEs) are also observed east of the Somali Current. During the winter monsoon, the Somali Current, Southern Gyre and Great Whirl are absent. The wind stress curl computed from the SAR data confirm this and do not show distinct circulation patterns or OLEs.