ESSO - Indian National Centre for Ocean Information Services

SCIENTIFIC IMPERATIVES

The Department of Ocean Development held a series of consultations with the Indian Scientific community during 1999-2000. The consensus was that India participates in the Argo Project and deploys 150 Argo floats. Argo data is considered and imperative for addressing the following issues:

The tropics provide a unique opportunity for climate predictions on time scales of seasons to years because, in contrast to mid and high latitudes, the mechanisms controlling short-term climate variations have a known significant predictable element. The circulation and temperature in the upper layers of the ocean in the tropics respond rapidly to changes in the wind. The resulting basin-scale changes in sea surface temperature are coupled to changes in global atmospheric circulation and associated rainfall distribution, leading to floods in some areas and drought in others. This direct coupling between the tropical oceans and atmosphere is the key to potentially successful climate predictions on time scales of seasons to years. During the last decade there has been considerable improvement in our understanding of the wind-driven circulation in North Indian Ocean basin in general, and in coastal waters in particular.

The circulation is forced by the stress exerted by monsoon winds that have a well-defined seasonal character. As a result, the wind-driven circulation too has a seasonal character. Influence of the circulation is felt in the top few hundred meters of the water column in the oceans ( the average depth of the ocean is 4000 m). It is now well established that a close link exists between the wind-driven coastal currents and the basin-wide currents. This implies that to monitor the events even along the coast of India is necessary to monitor the entire basin. Associated with the wind-driven circulation is a change in mass field, i.e. temperature and salinity (T-S). In fact, it is possible to uniquely determine the circulation in the top few hundred meters from data on T-S profiles together with altimeter data from satellites that are now in orbit. Argo data, together with altimeter data ( also available once every 10 days ), would make possible to monitor the circulation in the upper ocean and dynamic sea surface height. The inferred circulation could also be crosschecked with the other components of the observation system, such as the current meter moorings, moored data buoys and coastal tide-gauge network, that are now operational.

Very little is known about the circulation in the North Indian Ocean below the depth of about 500 m. It is known that large-scale thermohaline processes control the temperature and salinity field in these waters. Near surface waters that form at the subtropical convergence at approximately 40⁰ S can be traced all the way in the northern parts of the basin where these waters appear below the depth of about 1000 m. The Argo data, by providing profiles up to a depth of about 2000 m, will for the first time enable the Indian Oceanographer to study systematically the thermohaline circulation in the North Indian Ocean.

In essence, the Argo floats data set can be exploited by the oceanographer to understand oceanic processes that are unique to the North Indian Ocean. The two examples give above, near-surface wind-driven circulation, and thermohaline circulation at deeper levels, are two such processes. There must be others that are difficult to spell out at this stage, but which the oceanographic community is expected to define once the data become available for analysis.

The following are some questions that could be addressed:

What are the internal modes of variability, other than the annual cycle associated with the wind-driven near surface circulation? Recently, one such mode, called the Indian Dipole Mode, was discovered using the XBT data. It is quite possible there are other modes waiting to be discovered.
1. Do internal modes of variability have an impact on the monsoon-Ocean interaction?
2. What is the temporal variability of the low-salinity pool in the Bay of Bengal?
3. What are the regions where cross equatorial flow of heat and mass occur to close the heat budget of the North Indian Ocean basin?
4. Determine seasonal variability of heat budget of the seas around India.
5. Determine the factors that influence the SST in these seas.
6. Real-time forecasting of oceans through assimilation
7. Improve understanding (and hence prediction) the coupled atmosphere- ocean system