A Model of the Near-Surface Circulation of the Santa Barbara Channel: Comparison with Observations and Dynamical Interpretations

Abstract

Previous studies indicate the importance of wind, wind curl, and density differences in driving the near-surface circulation in the Santa Barbara Channel (SBC). Here model sensitivity experiments and dynamical analyses of the near-surface currents in the SBC are presented. Various approximations of the wind?from coarse-resolution European Centre for Medium-Range Weather Forecasts (ECMWF) archives to a high-resolution dataset that incorporates buoy, oil-platform, and land-based wind stations?are used. In some experiments, observed temperatures at 10 moorings are also assimilated into the model. Model solutions are sensitive to channel-scale [O(10 km)] wind distribution. Modeled currents forced by the ECMWF wind yield poor results when compared with observations. The simulation using the high-resolution wind (without assimilation) captures the observed spatial and seasonal patterns of the circulation, though the intensity is underestimated. With assimilation, the intensity is increased. In particular, the western-channel cyclone is reproduced well. Momentum analyses suggest that the cyclone is maintained by oppositely directed, time-dependent pressure gradients (PG) along the northern and southern coasts of the channel. These PGs are, in turn, caused by warming episodes probably related to wind relaxations. Momentum analysis also identifies along-channel PG (APG) as a dynamic index of the seasonal circulation. APG is strongly poleward in summer and autumn and becomes weak in winter. The poleward APG is eroded by equatorward wind bursts in late winter through spring during which period it changes sign to weakly equatorward. The APG becomes poleward again in early summer with the arrival of a large-scale warming signal from the Southern California Bight. The model does poorly in the eastern portion of the channel, in which region remote forcing at long periods (10?30 days) has been identified in previous observational studies. The model fails to reproduce the intense springtime (April) equatorward current (≈?0.2 m s?1) at the eastern channel entrance. The corresponding variance is also underestimated. The remote forcing is not accounted for in the model because climatological conditions are specified at the open boundary in the Southern California Bight.