The M2 Internal Tide over the Oregon Shelf

John J. Osborne (Oregon State)
A. L. Kurapov (Oregon State)
G. D. Egbert (Oregon State)
P. M. Kosro (Oregon State)

Interactions of the internal tide and wind-driven upwelling on the Oregon shelf are studied using a 1-km horizontal resolution ocean circulation model based on ROMS. The study period is May-August 2002, when data from the GLOBEC field program are available for model verification. Realistic time- and space-varying atmospheric forcing is provided by COAMPS. Open boundary conditions are a combination of a solution from a larger scale, 3-km resolution ROMS model (run without tidal forcing) and barotropic tide from a data-assimilating shallow-water model. Three cases are compared, forced by the tide only, winds only and the tide and winds in combination. Modeled subtidal and tidal variability on the shelf is in good agreement with time-series of mooring velocity observations.

The solutions have revealed "hotspots" of the M2 internal tide generation on the Oregon slope, as well as areas of intensified tidal energy dissipation. Despite day-to-day variability in the baroclinic tidal energy fluxes on the slope and shelf, the alongshore average flux on the shelf does not vary much. Resolution of bathymetry affects the area-integrated generation and dissipation of the internal tide energy on the slope more than the integrated baroclnic tidal energy flux from the slope to the shelf.