Abstract
Observational studies generally suggest that the formation of the Catalina 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 understand the eddy generation mechanisms, a high-resolution mesoscale model is initialized and forced on the lateral boundaries by NMC's large-scale objective analysis, and a detailed numerical study of the 26–30 June 1988 Catalina Eddy event is presented. The model results compare favorably with the observations and generally support the aforementioned mechanism of the eddy formation. It appears that a warm air mass over the bight resulting from adiabatic heating of low-level downslope flow deflected by the mountain barrier significantly helps create the alongshore 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 responsible for eddy formation, their spatial resolutions are too coarse to directly predict Catalina Eddy events that are of meso-β scales. However, the aforementioned model results with the large-scale objective analysis suggest the possibility of predicting an eddy event with a mesoscale model driven by outputs from an operational forecast model. A series of similar experiments were therefore performed using NMC's Medium Range Forecast (MRF) Model forecasts. These, model results suggest that, for at least three days into the future, the MRF model forecasts were able to predict synoptic-scale conditions that were essential to the development of this particular eddy event.
