Regional flux-adjustment

of the Unified Model

Regional flux adjustment is a logical extension from regional coupling. In the case of regional coupling, the sea surface temperatures are relaxed very strongly back towards a specified climatology in a particular region. This means that, in that region, the GCM is not coupled, but is actually working like an atmosphere-only model, with prescribed SSTs. In the case of regional flux adjustment, the ocean model predicts the SSTs which are then seen by the atmosphere. However, in this case a specified annual cycle of fluxes into (or out of) the ocean are provided in addition to the fluxes predicted by the atmosphere model. These fluxes have been pre-calculated in order to maintain the SST climatology of the model close to a prescribed state.

The uses of regional flux adjustment are perhaps not immediately obvious. Using global flux adjustments used to be the norm in coupled models in order to prevent the models drifting into a totally unrealistic state. Improvements to models over the years have made this unnecessary, and such techniques are certainly not acceptable in the context of climate change experiments. However, in specific cases they may still be useful for assessing the sensitivity of coupled models to particular errors in the mean state. The regional flux adjustment technique was used by Inness et al (2003) to study whether correcting systematic errors in the West Pacific in HadCM3 would have an impact on the propagation of the MJO in that region.

The flux adjustment technique is an extension of the regional coupling method described elsewhere on these help pages. The first step is to run a regionally coupled experiment to generate the flux adjustment file. The next steps are described by following the flux adjustment link below.