Regional coupling

of the Unified Model

A fully coupled global climate model is an extremely useful tool for climate prediction and research. The coupled climate system evolves freely with the atmosphere feeding back onto the ocean and vice versa. This means that there are many more degrees of freedom than in an atmosphere-only climate model where the atmosphere is driven by prescribed SSTs, which might be a mean annual cycle, SSTs from specific years or over an extended period. For research purposes it is sometimes desirable to use something in between the two - an ocean-atmosphere climate model in which the atmosphere and ocean are fully coupled in some regions, but in others the SSTs are prescribed to observed or climatological values.

There are several possible uses for a climate model which is coupled in some areas but with prescribed SSTs in others. One example might be that you wish to study the coupled climate response of a particular region of the Earth to ENSO events in the tropical Pacific. However, the fully coupled climate model may produce ENSO events which are unrealistic in strength, frequency of occurrence or geographical distribution of anomalies. Hence the remote responses of the climate system might also be expected to be unrealistic. A better experiment to investigate this issue would be to prescribe a realistic ENSO cycle in the tropical Pacific ocean, but allow the rest of the coupled climate system evolve freely. This is regional coupling.

Buwen Dong and Steve Jewson have developed a method for setting up regionally coupled versions of HadCM3, the Hadley Centre coupled GCM. These pages describe the technique and include links to the tools you need to do it for yourself. Click on the regional setup button below for details.