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Propagation of Velocity Discontinuities on Potential Vorticity Fronts

Joseph PedloskyDepartment of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

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Abstract

The propagation of finite-length velocity discontinuities along a potential vorticity front is studied. The front is oriented in a fundamentally north-south direction on the β-plane. The potential vorticity on either side of the front is constant.

According to a semigeostrophic theory, the shear disturbances propagate with a speed which depends on the difference of the deformation radius across the front and on the local depth, hB, of the moving fluid layer at the front. The disturbance steepens as it propagates. Breaking is predicted by the semigeostrophic theory at a time which depends inversely on the propagation speed and the initial steepness of the perturbation to the layer depth. Small velocity discontinuities will grow as they propagate.

Abstract

The propagation of finite-length velocity discontinuities along a potential vorticity front is studied. The front is oriented in a fundamentally north-south direction on the β-plane. The potential vorticity on either side of the front is constant.

According to a semigeostrophic theory, the shear disturbances propagate with a speed which depends on the difference of the deformation radius across the front and on the local depth, hB, of the moving fluid layer at the front. The disturbance steepens as it propagates. Breaking is predicted by the semigeostrophic theory at a time which depends inversely on the propagation speed and the initial steepness of the perturbation to the layer depth. Small velocity discontinuities will grow as they propagate.

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