HR: 10:35h
AN: OS51E-08    [PDF]
TI: A Modeling Study of the Flow Instabilities Associated With the Coastal Upwelling Front.
AU: * Durski, S M
EM: sdurski@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331 United States
AU: Allen, J S
EM: jallen@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331 United States
AB: A three-dimensional, sigma-coordinate, primitive equation model (ROMS) is used to explore the dynamics of instabilities associated with the coastal upwelling front and determine the role these instabilities play in across-shelf exchange processes. A collection of experiments are performed to both gain insight into the processes and understand their potential significance in the real ocean. Simulations are first performed with alongshore-uniform bathymetry and steady upwelling favorable winds applied to an ocean initially at rest to illuminate the development of the instabilities. A sixty-day-record of real wind forcing is then applied over this same domain to examine the response over multiple upwelling events. One advantage of this domain is that it allows analysis of alongshore averaged fields for comparison with two-dimensional upwelling simulations which do not exhibit the instabilities. The role of alongshore variations in bathymetry is then considered with both the steady and real wind forcing in a periodic domain with topography representative of the Oregon Shelf. With steady winds and alongshore uniform bathymetry an oscillatory pattern on a scale of approximately 8 kilometers is visible along the upwelling front by day 5. As the upwelling progesses, the small-scale peaks and troughs of this pattern coalesce to form a growing disturbance on the front of increasingly greater wavelength. The simulation with multiple wind events shows that these small scale oscillations reappear superimposed on the pre-existing patterns within several days of each strong upwelling favorable wind event. Comparison of the time and alongshore-averaged density sections from this run with identical two-dimensional simulations without the instabilities, reveal that the frontal disturbances lead to the presence of significantly higher density water in the surface boundary layer farther offshore. The rate of development of the instabilities is sensitive to the local shelf bottom bathymetry. Consequently, the simulations with variation in alongshore bathymetry reveal regions along the coast that are particularly conducive to the development of the frontal disturbances and show the subsequent variations in instability growth associated with advection of disturbances into regions with different shelf topography.
DE: 4219 Continental shelf processes
DE: 4255 Numerical modeling
DE: 4279 Upwelling and convergences
DE: 4528 Fronts and jets
SC: OS
MN: 2002 Ocean Sciences Meeting