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This picture shows some of the "parts" of a computer model that includes both the atmosphere and the ocean.
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Coupled Ocean-Atmosphere Models

Scientists use computer models to help them understand the Earth. Scientists who study the atmosphere use computer models of the atmosphere. Some scientists who study the oceans use computer models of the seas. Some scientists study both the atmosphere and the oceans. Those scientists use a special kind of model that includes both the seas and the air. These combined models are called "coupled models".

What is the difference between a coupled model and a model that isn't coupled? Let's look at an example. Computer models of the atmosphere keep track of many things, like how much carbon dioxide (CO2) is in the air. Some parts of the model keep track of how much CO2 is added to the air. For example, burning coal and gasoline adds CO2 to the atmosphere. Other parts of the model keep track of how much CO2 is taken out of the air. One way this happens is that oceans absorb CO2 from the air. In a normal uncoupled model of the atmosphere, scientists don't keep track of how much CO2 ends up in the oceans. The oceans don't change in that kind of model.

A coupled model is different. Changes in the atmosphere do cause changes in the ocean. Changes in the ocean part of the model can cause changes in the atmosphere part. So if lots of carbon dioxide moved from the atmosphere to the ocean, the ocean might get "full" of CO2. It might not be able to hold any more. Or it might take in more CO2 very slowly.

As you might guess, coupled models can be more realistic. So why don't scientists always use coupled models instead of uncoupled models? Coupled models are very, very complicated. It takes a lot of work to make sure the answers from them are right. It also takes a long time to run coupled models, even on fast supercomputers. Sometimes uncoupled models are good enough for certain types of problems. Other times scientists really need to use the more complex coupled models.

Last modified August 26, 2008 by Randy Russell.

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The Summer 2010 issue of The Earth Scientist, available in our online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.

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