Buoyancy-Driven Coastal Currents
OREGON STATE UNIV CORVALLIS
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The stability of a coastal upwelling jet and front was investigated using the primitive equations applied to a continuously stratified flow in geostrophic balance. A linear stability analysis explained the growth of two modes of instability with distinctly different horizontal scales. A long-wavelength mode was a modified version of a traditional baroclinic instability. A second, rapidly growing frontal instability was also found. The linear stability analysis was also applied to observed sections of salinity and velocity from the buoyancy-driven Alaska Coastal Current and, again, two modes of mesoscale variability were found. A three-dimensional, time-dependent, fine resolution numerical ocean circulation model was used to study the evolution of the unstable buoyancy-driven coastal jet. Early in the simulation, short-wavelength frontal instabilities grew and propagated along the jet. Eventually, the frontal instabilities were frictionally damped and the long-wavelength baroclinic instability became dominant. The baroclinic instability amplified into a series of backward-breaking waves whose crests eventually pinched off to form fresh, anti-cyclones while saline cyclones remained in the troughs. The scales of these eddies were consistent with those evident in maps of dynamic height from the Alaska Coastal Current.
- Physical and Dynamic Oceanography