A Numerical Study of Mesoscale Eddy Development over the Santa Barbara Channel

Abstract

The development of the “midchannel eddy” over the Santa Barbara Channel represents a mesoscale response of the large-scale airflow to the combination of the diurnal heating cycle over land surfaces, the curvature of the coastline, and the orientation of major ridges with respect to the coastline. In this paper we analyze and discuss the results of a numerical simulation of mesoscale airflow over the Santa Barbara Channel and adjacent land areas on 23–24 September 1985, with emphasis upon nocturnal mesoscale eddy development. Simulated winds are compared with SCCCAMP 1985 wind observations. Both simulation and observations indicate inception of a midchannel eddy in the vicinity of Santa Barbara during the late evening of 23 September, followed by westward and southward expansion of the eddy. Our analyses indicate that simulated midchannel eddy development is associated with the following sequence of events: 1) offshore-directed flow develops over coastal ridges in the early evening, associated with inertial rotation of the sea breeze; 2) a “warm pocket” appears south of the coastal ridge near Santa Barbara resulting in a hydrostatic pressure minimum at low levels; 3) easterly flow develops near the coast as an ageostrophic response to the pressure minimum, while westerly flow components are maintained over the southern part of the channel; and 4) the resulting eddy elongates as the easterly flow advects the warm pocket westward along the coast.