MICOM: An "Isopycnic" Ocean Model

These results place MICOM at the forefront of ocean modeling, not only because the Gulf Stream goes where it should, but also because MICOM -- which has a 15-year history -- has now proven that a significantly revised approach to modeling the ocean's vertical dimension works.

Ocean modeling began in the 1960s, but progress has lagged behind atmospheric models. The relative sparsity of observational data is one factor, but just as limiting, says Bleck, is the greater complexity of closed-basin systems like the ocean and the highly nonlinear equations required to describe buoyancy effects in sea water.

In particular, conventional ocean modeling has been vexed by distortions in the interaction between the ocean surface, which captures heat from the sun, and deeper, colder regions. "The ocean is heated from above," explains Bleck. "Warm water sits on top of cold water, and you need to make sure that this temperature contrast doesn't get diminished over time." The problem has been that it is inherent in the numerical scheme of conventional models for heat to trickle between warm and cold regions.

"We have designed a set of equations," says Bleck, "where this type of heat diffusion is removed." The ocean is divided into 11 layers, each of which maintains its own density -- hence the term isopycnic, meaning constant density. Each layer is separate, as if divided by plastic sheets from the layers above and below it -- greatly reducing the spurious effects of heat diffusion.

The T3D results at Pittsburgh show that this approach works. "It was not clear 10 years ago," says Bleck, "that this would be practical. We've proven that the equations from this more sophisticated scheme are numerically solvable. This is important for climate research."

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