OBSERVATIONS OF THE EKMAN BALANCE AT 8-DEGREES-30' N IN THE ARABIAN SEA DURING THE 1995 SOUTHWEST MONSOON

The Ekman transport is estimated from two sets of hydrographic and shi pboard acoustic Doppler current profiler (ADCP) velocity observations made during June and September 1995, during the southwest monsoon in t he Arabian Sea. Both sets of measurements were made along latitude 8 d egrees 30' N, designated as World Ocean Circulation Experiment (WOCE) line I1W, from Somalia to Sri Lanka. The Ekman transport estimates cal culated from ageostrophic velocity were southward: 17.6 +/- 2.4 10(6) m(3) s(-1) in June and 7.9 +/- 2.7 10(6) m(3) s(-1) in September. Thes e direct estimates were in good agreement with those predicted by the Ekman balance using both shipboard and climatological winds. The verti cal structure of the ageostrophic velocity and the stratification were quite different between the two occupations of the transect. The wind -driven momentum was confined to a very shallow layer in June (about 5 0 m) and the surface layer was strongly stratified, with a maximum sal inity layer at depths between 50 and 70 m. The ageostrophic velocity p enetrated much deeper in September (to about 160 m) and the pycnocline was correspondingly deeper. In both cases, the Ekman transport penetr ated beneath the mixed layer, to the top of the pycnocline.