The Effect of Inner Shelf Processes on Surface Drifter Trajectories and Dispersion

Matthew S Spydell, University of California San Diego, Scripps Institution of Oceanography, La Jolla, United States, Falk Feddersen, University of California San Diego, La Jolla, United States, Jamie MacMahan, Naval Postgraduate School, Oceanography, Monterey, United States, Jim Thomson, University of Washington, Seattle, United States, Michael Kovatch, Scripps Institution of Oceanography, La Jolla, CA, United States and Melissa Moulton, National Center for Atmospheric Research, Climate and Global Dynamics, Boulder, United States
Abstract:
GPS-tracked surface drifters (approximately 1 m depth) were released on 14 days in Sep. and Oct, 2017 within the inner shelf off of Pt Sal, CA. Each release consisted of approximately 25 drifters. The 2-24 hour long trajectories show a multitude of behaviors: with drifter velocities approximately constant over the duration of the release and the scale of the drifter cluster, to changing on short time- (minutes) and space (10--1000 meters) scales. The inner shelf processes responsible for the drifter trajectories include wind driven flow, internal bores, headland eddies, and Stokes drift. These processes are investigated using both drifter and mooring data. The effect of these processes on scale-dependent velocity gradients (e.g. vorticity and divergence) and drifter acceleration is examined. Furthermore, the relationship between these processes and drifter dispersion is analyzed. For these drifter releases, internal bores greatly affect drifter trajectories, velocity gradients, and dispersion.
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