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Ocean circulation pathways in the Bay of Bengal : Observations and model results

 

Peter Hacker

University of Hawaii

 

The Bay of Bengal sector of the Indian Ocean has some of the warmest sea surface temperatures and strongest atmospheric convection found on earth, but there have been very few observations of the upper ocean. The region has high freshwater input both from precipitation and river discharge. Because of the warm sea surface temperatures and the strong moisture and energy exchanges with the atmosphere, recent studies suggest that the region plays a key role in the coupled atmosphere-ocean, monsoon system. However, the role is poorly understood.

Our observational knowledge of the region is based mainly on monthly climatologies : ship-drift surface currents; air-sea fluxes; mixed-layer depth based on temperature only; and temperature and salinity fields from hydrographic data. During 1995, the WOCE Expedition to the Indian Ocean provided high quality temperature, salinity and velocity data which provide snapshots of the vigorous circulation pathways and the complex mixed layer and barrier layer structure. Since 1995, drifters and floats have continued to provide data on surface currents and upper ocean temperature and salinity.

Extensive modeling of the Indian Ocean has been conducted during the past decade. Most of our ideas about the time varying circulation are based on these more-or-less realistic model simulations, which show strong variability on intraseasonal through interannual time scales. Interannual variability is expected from the variability of atmospheric forcing, the river input, and the Indonesian Throughflow. The lack of modern, high-resolution (in both space and time) data has prevented the careful evaluation of the models. However, recent data enable some preliminary intercomparisons and suggest that realistic OGCMs will need to include salinity as well as temperature, will need to have high vertical and horizontal resolution to resolve upper ocean structures, and may have to include tidal mixing.

In light of our present observational knowledge, needed ocean observations are proposed.

 

 

 

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