IUGG 2003 Abstract

P05 The Physical Oceanography of the Indian Ocean Monday, June 30 PM Location: Site B, Room 23 Presiding Chairs:W. Han, J.S. Godfrey

TIME [ 1510 ] [ P05/30P/B23-004 ]

EVIDENCE FOR A THERMAL DOME IN THE ARABIAN SEA DURING WINTER MONSOON

Prasad G. THOPPIL(Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USA)

Julie L. MCCLEAN(Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USA) Motoyoshi IKEDA ( Division of Ocean and Atmospheric Sciences, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, JAPAN )

In the southern Arabian Sea, the shoaling of isotherms at subsurface levels leads to cooling at 100 m by 2-3 degrees Celsius relative to the surrounding waters during the winter monsoon. We identify this subsurface upwelling zone as the Arabian Sea Dome (ASD). Seasonal variations of the ASD are studied using results from an eddy-permitting ocean general circulation model in conjunction with hydrography and satellite altimetry. The ASD first appears in the southeastern Arabian Sea during October, matures during November-December extending across the entire southern Arabian Sea (along 5N). It begins to weaken in January and dissipates by March in the southwestern Arabian Sea. The local Ekman upwelling induced by the cyclonic wind-stress curl of the winter monsoon generates the ASD in the southeastern Arabian Sea. The generating mechanism of the ASD is further confirmed bytwo controlled experiments. In the first experiment, wind-stress is held constant during the winter monsoon whereas in the second experiment the wind-stress is kept constant during the summer monsoon. Since there was no local Ekman upwelling associated with the winter monsoon winds, the ASD failed to develop in the first experiment. In contrast, the life cycle of the ASD is perfectly simulated by the seasonal wind variations in the Arabian Sea during the winter monsoon. The ASD decays due to weakening of the cyclonic curl of wind and arrival of a westward propagating downwelling Rossby wave (Southern Arabian Sea High) from the eastern Arabian Sea. Comparison of a variety of observations and model results revealed good agreement in location, time of appearance and decay of the ASD.