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The Effect of Current-Induced Stress Perturbation On Baroclinic Rossby Waves in a Continuously Stratified Model

Lian XieDepartment of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

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Claes RoothRosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida

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Abstract

A shear stress at the air–sea interface is induced by the presence of surface currents. In the case of isotropic wind, a quadratic stress law leads to a stress curl proportional to and opposing the surface current vorticity. This causes a spindown effect on the surface vorticity field at a rate proportional to the characteristic wind speed. This effect of surface vorticity spindown or friction on propagating baroclinic Rossby waves is analyzed in a continuously stratified system with well-mixed boundary layers above and below it. In this system, both bottom friction and surface friction modulate the baroclinic Rossby waves in the stratified interior each time a wave group is reflected at the lower and the upper interfaces. The reflection coefficient and the corresponding spatial attenuation rate are calculated for various values of wave frequency, wind speed, and interior stratification. Both bottom friction and surface friction are important dissipation mechanisms for the baroclinic Rossby waves. Within a normal parameter range appropriate for deep oceans, the nondispersive, long Rossby waves are more effectively damped by surface friction than by bottom friction, whereas the dispersive, short Rossby waves are primarily damped by bottom friction.

Abstract

A shear stress at the air–sea interface is induced by the presence of surface currents. In the case of isotropic wind, a quadratic stress law leads to a stress curl proportional to and opposing the surface current vorticity. This causes a spindown effect on the surface vorticity field at a rate proportional to the characteristic wind speed. This effect of surface vorticity spindown or friction on propagating baroclinic Rossby waves is analyzed in a continuously stratified system with well-mixed boundary layers above and below it. In this system, both bottom friction and surface friction modulate the baroclinic Rossby waves in the stratified interior each time a wave group is reflected at the lower and the upper interfaces. The reflection coefficient and the corresponding spatial attenuation rate are calculated for various values of wave frequency, wind speed, and interior stratification. Both bottom friction and surface friction are important dissipation mechanisms for the baroclinic Rossby waves. Within a normal parameter range appropriate for deep oceans, the nondispersive, long Rossby waves are more effectively damped by surface friction than by bottom friction, whereas the dispersive, short Rossby waves are primarily damped by bottom friction.

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