Spring evolution of Arabian Sea High in the Indian Ocean

The seasonal formation of a large anticyclonic circulation pattern, Southern Arabian Sea High (SAH), appears in the southern Arabian Sea during the northeast monsoon. SAH is studied on the basis of the recent observations that include the World Ocean Circulation Experiment (WOCE)/Tropical Ocean-Global Atmosphere (TOGA) experiment drifting buoys along with TOPER/ERS-2 satellite altimeter data in conjunction with the climatological hydrography observations. The SAH fortes west of the Laccadive High (LH), first appears in January, and grows rapidly in situ to form a well-developed anticyclonic eddy, extending across the southern Arabian Sea by March. The center of the eddy is similar to65degreesE, 5degreesN. The SAH is bounded by a strong eastward current to the north and a weak southward flow between 65degrees and 70degreesE, which separates SAH from the LH. The westward flowing North Equatorial Current (NEC) is on the southern flank. A strong northward flow along 55degreesE during January and February marks the western boundary. SAH propagates westward as a Rossby wave between March and April. The arrival of SAH in the western boundary in April is accompanied by intensification of current along the coast of Somalia. In May, part of the SAH has subsequently moved northward to form an anticyclonic eddy with an apparent center 13degreesN, 53degreesE in the vicinity of the Gulf of Aden (Gulf of Aden Eddy (GAE)). The GAE extends horizontally nearly 600 km (along 13degrees) and is vertically extended down through the upper main thermocline to similar to250 m. Comparisons of hydrography, buoy, and altimetry reveal a good agreement in eddy size, location, and time of appearance of the GAE.