Tidal currents in a topographically complex channel

Abstract

The Santa Barbara Channel off Southern California constitutes a topographically complex channel that is open at both ends. Tidal sea level oscillations are well explained by a north- westward propagating Kelvin wave. Tidal currents vary at a multitude of topographic and temporal scales and cannot be explained by linear Kelvin wave dynamics alone. The analysis reveals three regions with distinctly different tidal currents. In the deep central basin and along a narrow northern shelf tidal currents are weak (<5 cm/s) while at the eastern channel entrance they are enhanced (15 cm/s). In a third region, tidal currents are particular strong (>30 cm/s) and tidal particle excursions are similar to the shelf width. Applying spectral and harmonic data analysis techniques, I distinguish between predictable (62% of the variance) and intermittent (38% of the variance) tidal currents. More than 94% of the latter are baroclinic, while the variance of the predictable tidal currents is equally distributed between baroclinic and barotropic motions. Two empirical orthogonal functions explain 87% for the predictable but only 61% of the intermittent baroclinic variance. Intermittent tidal currents vary little in space and can reach 15 cm/s in amplitude during a 2-day period, however, in the temporal mean these unpredictable tidal current are only 5 cm/s. In contrast, the predictable tidal currents vary in space from 5 to 50 cm/s during any 2-day period.