The mathematical equations which describe the motions of the ocean are based on Newton's Laws and the laws of thermodynamics. A realistic representation, or "model," of the ocean gives rise to equations which are too complicated to be solved by ordinary mathematical methods. As a practical approach to this problem, oceanographers at COAS create approximations to these equations which can be solved numerically on a computer. This procedure is quite similar to that used to create weather forecasts. The computer programs which find these approximate solutions are called "numerical models."

Numerical models of ocean circulation are among the most demanding tasks performed by computers today. Although some simple models of a small region of the ocean over a short time period can be solved on a personal computer, realistic global models take thousands of hours on the fastest super computers available. One way to get this kind of computational power is to link many computers together to work on a problem, a strategy known as "parallel computing." Much of the numerical modeling work done at COAS utilizes a massively parallel Connection Machine CM5 which consists of 64 fast processors linked together by a fast network and coordinated by special software. Other modeling work at COAS uses a Silicon Graphics Power Challenge and an IBM SP2. The computer facilities at COAS are among the finest available at any oceanographic research institution anywhere in the world.

Even when the fastest computers are used, numerical models are only approximations of the full dynamic and thermodynamic equations. Their solutions are therefore also only approximations. One way to correct for errors in the model solutions is to apply a procedure known as "data assimilation," which blends the model approximations with observations of the real ocean in a least-square error sense. This blending takes account of errors in the model dynamics and thermodynamics, as well as measurement errors in the observations.

In the past, oceanographic data was collected primarily by ships, moored observations and drifting floats and buoys, which are all very expensive to maintain. The Tropical Ocean-Global Atmosphere (TOGA) array of moorings maintained by the National Oceanic and Atmospheric Administration (NOAA) in the tropical Pacific is an important source of such data. This mooring array incorporates instruments which continuously measure wind speed, water temperature, and ocean currents across the tropical Pacific Ocean. COAS oceanographers are using these data together with numerical models to improve forecasts of El Nino. Other important sources of oceanographic data are satellite observations of sea surface elevation, sea surface temperature and surface winds from several NASA satellites launched in recent years. (Satellite Oceanography Theme Page) Satellites provide the comprehensive global coverage needed for assimilation into global ocean circulation models. COAS oceanographers are using these satellite data to improve the prediction of tides around the world, as well as to improve model simulations of large-scale ocean currents.

---