Moored observations of upper-ocean response to the monsoons in the Arabian Sea during 1994–1995

The role of surface forcing in the semiannual evolution of the upper-ocean temperature, salinity, and velocity fields in the Arabian Sea is examined. To do so, variability in the upper ocean in the central Arabian Sea was observed from an array of moorings deployed from October 1994 to October 1995. The Northeast (NE) Monsoon was characterized by moderate winds, clear skies, and dry air; sea-surface temperature (SST) dropped by 31C; the ocean lost an average of 19.7Wm 2 and the mixed layer deepened by 100m in response. The Southwest (SW) Monsoon was accompanied by strong winds, cloudy skies, and moist air; the ocean gained an average of 89.5Wm 2 but SST dropped by 5.51C and the mixed layer deepened to almost 80m. The response to the NEMonsoon included daily cycling in the depth of the mixed layer in response to the diurnal cycle in the buoyancy forcing and a weak local, wind-driven response. Stronger windforcing during the SW Monsoon dramatically reduced diurnal restratification, and a clearer signal of local, wind-driven flow in the upper ocean was found. The strongest velocity signal in the upper ocean, however, was the flow associated with mesoscale geostrophic features that passed slowly through the moored array, dominating the current meter records in the first part of the NE Monsoon and again in the latter part of the SW Monsoon. One-dimensional heat and freshwater balances, which held at other times through the year, broke down during the passage of these features. r 2002 Published by Elsevier Science Ltd.