Supercomputers map global ocean currents

TWO US oceanographers have used powerful supercomputers to perform the best-ever simulation of the world's ocean movements -- an important step towards forecasting how changes in ocean circulation will affect global climate over the next century.

Albert Semtner of the Naval Postgraduate School in Monterey and Robert Chervin of the National Centre for Atmospheric Research in Boulder created a model that provides a detailed view of ocean circulation over the entire globe. Previous models have covered only a small part of the oceans or have had much fewer details (Science, Vol 260, No 5104).

The new model is able to simulate even small storms called eddies, which play an important role in transporting heat and salt around the oceans.

The most striking success of Semtner and Chervin's model was the duplication of the "conveyor belt" flow, a vast looping ocean current that connects the Pacific, Atlantic and Indian Oceans, which had been difficult to map in its entirety. The current transports large amounts of surface water from the Pacific to the Atlantic Ocean. On reaching coastal Iceland, the water loses its heat to the cold north winds, thereby keeping Europe 6oC warmer than it would be otherwise.

The simulation of global ocean currents in a model bodes well for efforts to recreate on computers the entire climate system -- the oceans, atmosphere and polar ice sheets -- in enough detail to predict climate change.

In their attempt to model the oceans, Semtner and Chervin were aided by the greater computing power of a new generation of supercomputers, which work by parallel processing. The supercomputer operates on the principle of splitting a problem into several parts and solving them separately and simultaneously, thereby greatly reducing computing time and overcoming limitations encountered in previous attempts to model the ocean movements.

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