Catalina eddies and coastally trapped disturbances

Observations show that coastally trapped disturbances (CTDs) often accompany Catalina eddies that appear in the southern California bight. In a previous modeling study of CTDs using simple environments and forcings, simulations of CTDs also evolved a mesoscale eddy that played a critical role in CTD formation and evolution. In this study the simple environments and forcings are extended to model the southern California bight, and simulations produce both Catalina eddies and CTDs. The simulated Catalina eddies and the mesoscale eddies in the previous CTD studies are dynamically equivalent. The primary mechanism for eddy formation in the simulations is lee troughing, and eddies and CTDs are produced provided that 1) there is sufficient stratification in the environment; 2) the offshore flow is of sufficient strength, breadth, and duration; and 3) there is sufficient terrain to produce significant lee troughing. The simulations show that CTDs can propagate out of the bight region when synoptic winds leading to eddy formation are northeasterly onto the bight, but are blocked by the prevailing marine layer northwesterlies for the case where the synoptic winds are northwesterly. Potential vorticity (PV) generated during the course of eddy formation does not significantly contribute to the eddy structure or CTD formation.