Surface circulation in the Santa Barbara Channel: An application of high frequency radar for descriptive physical oceanography in the coastal zone

Surface circulation of the Santa Barbara Channel (SBC) is difficult to characterize due to several confounding attributes: the confluence of contrasting water masses that occurs there, the local wind stress forcing which is highly dynamic in its spatial and temporal distribution, and the channel's irregular coastline and topography. Observation is also problematic because it is impractical to sample surface currents over a large area using moored or drifting sensors with sufficient resolution to capture its significant features with a high degree of detail for extended sampling periods. In this research the emergent technology of high frequency (HF) radar is used to monitor surface flow structures inside of the SBC. Using HF radar, the upper meter of the water column is observed continuously for four years at hourly intervals on a 2 km spatial grid. Locally and remotely forced flow patterns are defined and explained.; Empirical orthogonal decomposition of the wind stress field in the vicinity of the SBC reveals that the area is dominated by two large-scale patterns of variability. Four distinct synoptic wind forcing regimes with seasonal tendencies are defined based on large positive and negative amplitudes of the modes. It is found that previously defined circulation patterns, Upwelling, Relaxation, and Convergence, each correspond to individual forcing regimes. Moored and HF radar observations agree well; the former describes flow along the basin shelf breaks; the latter resolves flow over the central basin.; A remotely forced pattern of alternating cyclonic and anticyclonic vortices that propagates westward is investigated. The sequences last up to a few months and occur intermittently throughout the year. Complex empirical orthogonal function decomposition in the 10–20 day passband partitions variance into two dominant modes; the first represents the vortices with an average period of 14.4 days; the second represents alongshore fluctuations with an average period of 13.3 days. Mode 2 is interpreted as a coastal trapped wave since the period and along-shore flow are consistent with previous observations and predictions. Comparison with a simple analytical model suggests that mode 1 is a resonant response of the basin in the form of a trapped topographic Rossby mode.