ON THE REMOVAL OF GRAVITATIONAL NOISE IN NUMERICAL FORECASTS

There are several successful techniques for removing relatively high-f requency ''noise'' due to propagating inertial-gravitational waves in model forecasts. Not all behavior that is sometimes considered noise i s necessarily spurious, however, including that due to tidal forcing. Published evidence of the natural existence of high-frequency behavior within numerical weather prediction and general circulation models is briefly reviewed and some additional evidence with yet another model is introduced. In this new model, the existence of local diabatic bala nces is also examined. Imposing balances or filters at scales where hi gh-frequency oscillations are naturally and realistically occuring cau ses errors which may become more significant as we demand more accurat e models and atmospheric analyses. The intention of this paper is to s timulate further research into the naturally occuring high-frequency b ehavior in numerical models, as well as in the atmosphere, for the pur pose of improving both models and atmospheric analyses.