The structure of the upper ocean, atmosphere and heat fluxes - Tropical Indian Ocean

Sea surface temperatures in the tropical Indian Ocean have been shown to be inversely related to South African summer rainfall, making advanced predictions of this rainfall practicable. Such predictability has enormous potential economic benefits. However, these predictions have been purely statistical; very little is currently known about the marine-atmospheric processes in the Indian Ocean tropics. To address this lack of information, the structure of the upper ocean and lower atmosphere as well as the surface heat fluxes in the tropical Indian Ocean have been investigated. This was done by a special measurement programme on a research cruise in the region. Global gridded meteorological data have been used to complement the shipboard observations. Heat fluxes have been computed from the cruise observations and related to the main atmospheric patterns at the time. These patterns were identified from principal components analysis. Air-sea interaction could thus be estimated over the full tropical Indian Ocean. It is found that the thermocline depth is linked to the cyclonic ocean current shear and to the overlying distribution of wind stress curl. The meridional advection of air into the central Indian Ocean region is shown to modulate the characteristics of the atmospheric boundary layer in the tropical Indian Ocean. The maximum turbulent heat and moisture transports to the atmosphere are found near cyclonic atmospheric disturbances. These are the first reliable observations of the heat and moisture fluxes in that part of the tropical Indian Ocean implicated in South African rainfall. It is clear from this investigation that the synoptic atmospheric systems and the meridional flow of air are critical to enhanced atmospheric convection in the region