ROSSBY-WAVE BREAKING, MICROBREAKING, FILAMENTATION, AND SECONDARY VORTEX FORMATION - THE DYNAMICS OF A PERTURBED VORTEX

The behavior of an isolated vortex perturbed by topographically forced Rossby waves is studied using the method of Contour Dynamics. For a s ingle-contour vortex a distinct forcing threshold exists above which t he wave breaks in a dynamically significant way, leading to a disrupti on of the vortex. This breaking is distinguished from the process of w eak filamentary breaking described by Dritschel and classified here as microbreaking; the latter occurs in nondivergent flow even at very sm all forcing amplitudes but does not affect the vortex in a substantial manner. In cases with finite Rossby deformation radius (comparable wi th the vortex radius) neither breaking nor microbreaking occurs below the forcing threshold. In common with previous studies using high-reso lution spectral models, the vortex is not diluted by intrusion of outs ide air, except during remerger with a secondary vortex shed previousl y from the main vortex during a breaking event. The kinematics of the breaking process and of the vortex interior and the morphology of mate rial ejected from the vortex are described. When the Rossby radius is finite there is substantial mixing in the deep interior of the vortex, even when the vortex is only mildly disturbed. Implications for the s tratospheric polar vortex are discussed.