SIMULATION AND PREDICTION OF THE CATALINA EDDY

Observational studies generally suggest that the formation of the Cata lina Eddy in the bight of southern California results from interaction between the synoptic-scale northerly flow and the topographic barrier along the southern California coast. In an attempt to better understa nd the eddy generation mechanisms, a high-resolution mesoscale model i s initialized and forced on the lateral boundaries by NMC's large-scal e objective analysis, and a detailed numerical study of the 26-30 June 1988 Catalina Eddy event is presented. The model results compare favo rably with the observations and generally support the aforementioned m echanism of the eddy formation. It appears that a warm air mass over t he bight resulting from adiabatic heating of low-level downslope flow deflected by the mountain barrier significantly helps create the along shore and offshore pressure gradients favorable for the generation of a cyclonic vorticity. Although current operational forecast models are capable of often accurately predicting the large-scale flow responsib le for eddy formation, their spatial resolutions are too coarse to dir ectly predict Catalina Eddy events that are of meso-beta scales. Howev er, the aforementioned model results with the large-scale objective an alysis suggest the possibility of predicting an eddy event with a meso scale model driven by outputs from an operational forecast model. A se ries of similar experiments were therefore performed using NMC's Mediu m Range Forecast (MRF) Model forecasts. These model results suggest th at, for at least three days into the future, the MRF model forecasts w ere able to predict synoptic-scale conditions that were essential to t he development of this particular eddy event.