A NEW APPROACH FOR COUPLING A LIMITED AREA MODEL TO A GCM FOR REGIONAL CLIMATE SIMULATIONS

A new method of nesting a high-resolution limited area model (LAM) in a low-resolution global model (GCM) is proposed for the purpose of conducting regional climate simulations. It is tested with a few feasibility studies of month-long time integrations of the LAM. The conventional method of embedding a LAM in a larger area model is to couple the inner to the outer model in terms of lateral boundary conditions in real space. In the present method, the concept of a spectral boundary in wavenumber space is the key to joining a high-resolution LAM to a low-resolution GCM. In practice the new technique of combining the two different resolution models is to replace the large-scale fields of the LAM with the corresponding large-scale fields supplied externally from the GCM at a selected regular time interval. The present experiments showed that the time integration was very smooth over a period of one month, and that the mesoscale features associated with the large-scale supplied from the GCM were well simulated, suggesting that the new method is encouraging for regional mesoscale climate simulations.