Modeling Flow Over Steep Topography with Strong Stratification:
The Circulation around Astoria Canyon
Michael Dinniman and John Klinck
Center for Coastal Physical Oceanography
Old Dominion University
Submarine canyons along continental shelf edges are important
topographical features that can have large impacts on coastal processes.
The combination of steep topography and strong stratification that can be
found makes this a challenging test case for terrain-following circulation
models. The Regional Ocean Modeling System (ROMS) was used in a 83km x
100km domain off the U.S. West Coast, centered on Astoria and Willapa
Canyons, in order to compare model results to an extensive velocity and
temperature data set in Astoria that was obtained at small enough spatial
and temporal scales to resolve the time-dependent circulation over and in
the canyon. The model horizontal resolution (~ 300m x 420m) was fine
enough to resolve the narrow (7km) Astoria Canyon and minimal bathymetric
smoothing was used.
The mean horizontal flow, as measured by comparisons of flow vectors and
relative vorticity, reproduced the observations moderately well. However,
the model upwelling did not match the observed upwelling, as estimated by
cross-sections and time histories of temperature and vertical velocity,
and showed the model to be vertically "stiff" in the canyon. Sensitivity
studies show the effect of different pressure gradient and tracer
advection schemes that have recently been implemented in ROMS. Some
possible causes of the differences between the observations and the model
that are being investigated include vertical advection errors, wind
forcing details and initial and offshore density structure.