Data assimilation model study of wind effects in the Santa Barbara Channel

Abstract

Seasonal mean circulation in the Santa Barbara Channel (SBC) consists of poleward flow on the northern shelf and equatorward flow on the southern shelf. While the equatorward flow is in the direction of the persistent, upwelling‐favorable wind, the inshore poleward flow is against the wind. The channel circulation also has a strong seasonal signal that the cyclonic circulation strengthens considerably in spring and summer. A three‐dimensional model is used to simulate the observed currents over an 8‐month period from January to August 1994. The model assimilates the moored temperature and salinity data obtained from a comprehensive circulation study in the SBC‐Santa Maria Basin (SMB). The model also incorporates surface wind forcing; the mesoscale wind stress pattern is derived from a dense network of weather buoys. The model simulation reproduces well the surface mean currents and their seasonal (monthly) variability. The transient (less than seasonal) model velocity response consists of two fundamental modes, a wind‐forced mode and an alongshore pressure gradient‐forced mode. The wind‐driven circulation is concentrated west of the channel in the SMB. The alongshore pressure gradient‐forced motion is concentrated in the channel along the northern coast. Analysis of the evolution of inshore poleward current suggests that the spring transition in this region may coincide with the end of the winter storm season.