Ocean-atmosphere Structure in the Tropical Indian Ocean during a Ship Cruise 1995/96

Abstract

The structure of the upper ocean and surface atmospheric conditions are described during a ship cruise across the central Indian Ocean from December 1995 to January 1996. In situ data on currents, temperature, salinity and surface heat fluxes are described and compared with expected climatological values. Thermocline uplift in the 6-7°S latitude band is linked to the cyclonic shear of near-surface currents. A comparison of quiescent and windy periods demonstrates that evaporative fluxes become amplified near cyclonic vortices fed by southerly meridional winds. The ocean density structure is influenced by salinity gradients, driven by the precipitation-evaporation balance. Near the inter-tropical convergence zone (ITCZ), freshwater fluxes create a stable surface layer and helps to maintain the eastward equatorial counter-current. An analysis of the atmospheric boundary layer from NCEP re-analysis data seeks to place the in situ results into the context of weather conditions at the time of the cruise. Further studies of this kind will improve our understanding of relationships between the Indian Ocean monsoon and surrounding climates.