Modeling Coastal Upwelling on the Inner Shelf Near Pt. Sal, California

Coastal upwelling is a common and generally well understood occurrence along the California coast. However, the circulation during coastal upwelling favorable winds on the inner shelf in the vicinity of headlands and complex bathymetry such as that near Pt. Sal, a 5km headland in southern California, is much more complicated. The circulation is influenced not just by the complex bathymetry and coastline, but also by the confluence of distinct alongshore currents, e.g., the California Undercurrent, flow from upwelling shadow zones, and upwelling plumes. In order to better understand the interactions of all these factors a numerical modeling system is used to simulate all these processes. The numerical model, Regional Ocean Modeling System (ROMS) is used for simulations during upwelling favorable wind periods, June-July 2015 and July-September 2017, occurring during the time period of the pilot and full inner shelf DRI experiments. A set of nested model grids downscale from a domain of the US west coast and Eastern Pacific (resolution 3km), to continental slope and outer-shelf region from the Southern to Central California (resolution 1km), to the region from Point Conception to south of Monterey Bay (resolution 600 m), to the interior Point Sal region (resolution 120 m, and resolution 40 m). Several time periods with upwelling favorable winds are simulated and three-dimensional particle trajectories are calculated to analyze the circulation pattern on these periods. As a result, characteristics of the coastal circulation, circulation boundary, upwelling front, convergence/divergence, and stratification, are described. The circulation pattern is analyzed by linking the forcing mechanisms with three-dimensional momentum balances at different locations across the inner shelf. Finally, the dominant forcing mechanisms acting on the different regions north and south of the headland are identified.