On the adjustment of azimuthally perturbed vortices

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Abstract

A series of numerical experiments with a reduced‐gravity, quasi‐geostrophic model were performed to investigate the adjustment of vortices to large‐amplitude perturbations of azimuthal modes 2 and 3. The results indicate that for vortices with length scales near the radius of deformation, almost 100% of the azimuthal mode energy is transferred to the axisymmetric flow. The time scale is of the order of the circulation time scale but exhibits a strong dependence on the perturbation mode number. The β plane cases show that this strong axisymmetrization tendency is almost completely unaffected by variations in the Coriolis parameter. The energetics of the perturbed β plane cases are virtually indistinguishable from the energetics of the unperturbed cases after 2–3 circulation periods, except for the cases with the strongest perturbations. Vorticity plots reveal that in the most perturbed cases, excess vorticity in the ends of the ellipse is removed in the form of elongated streamers. In some regions of the parameter space, these streamers roll up into cyclone‐anticyclone pairs.

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