REDUCING PHASE AND AMPLITUDE ERRORS IN RESTORING BOUNDARY-CONDITIONS

Restoring boundary conditions are often used to drive ocean general ci rculation models. As typically used, such conditions impose time lags and amplitude errors in the seasonal cycle of the model surface tracer fields. Restoring boundary conditions also damp out the high-frequenc y components of the forcing with more damping for higher frequencies; thus, models using such conditions systematically underrepresent high- frequency variability in the surface tracer fields. A solution to thes e problems is presented for use when the forcing field is known before hand. It is shown that this new formulation significantly reduces the time lags associated with the traditional form of restoring boundary c onditions and improves the model's representation of surface variabili ty. The new condition has no run-time overhead and does not impose any additional restrictions on the ability of the model to deviate from o bservations. The results of using the new boundary condition in an oce anic general circulation model are shown for cases with both monthly a nd weekly forcing.