In a tropical cyclone, the concentrated potential vorticity (PV) source due to heating in a circular eyewall can result in a reversal of the radial PV gradient, allowing the vortex to become barotropically unstable. In this manner an axisymmetric vortex can develop asymmetries, redistribute PV through chaotic nonlinear mixing, and eventually resymmetrize with a different, stable structure. Recent studies of this process in the non- divergent barotropic model (Schubert et al., 1998) have helped provide insight into diverse aspects of hurricane dynamics, including the development of spiral bands and mesoscale vortices, the existence of polygonal eyewalls, and asymmetric eye contraction.
This paper generalizes these results to the shallow water model, investigating three aspects of PV redistribution in shallow-water vortices. First, we consider the initial growth of asymmetric perturbations to a barotropically unstable vortex using linear stability analysis. Second, we investigate the nonlinear evolution and eventual symmetrization of the vortex using a Fourier spectral model. Third, we compute approximate solutions for the final vortex structure using the minimum enstrophy and maximum entropy principles. A major focus of this work is to investigate the differences between the nondivergent and divergent barotropic results, and thus to understand the limitations and range of validity of the simpler model.
Note:
We request that the following three papers be presented in the same session, in this order:
Schubert et al. (abstract #1261)
Kossin (abstract #1275)
Fulton, Schubert, and Montgomery (this abstract)
Thanks!