title: Asymmetric evolution of eddies in rotating shallow water.
abstract: It is demonstrated that cyclones evolve in a way different from that of anticyclones in rotating shallow water. The anticyclones merge and eventually take circular coherent forms, but cyclones are elongated with active enstrophy cascading. This asymmetric evolution is strengthened with increasing surface displacements. When the initial surface displacement exceeds a certain critical value, the initial elongation of a cyclonic ellipse ends up with splitting in two cyclones. This splitting of the cyclonic ellipse is always associated with the first appearance of a saddle point inside the core, due to irrotational, ageostrophic motion. The appearance of the saddle point inside the core seems to be a necessary condition for splitting of the core of the cyclonic ellipse with surface displacements. The linear stability analysis of the elliptical vortex is consistent qualitatively with both of the simulation results and the kinematic axisymmetrization/elongation principle.
authors.affiliation: Department of Physics, Graduate School of Science, Kyushu University, Fukuoka, 812 JapanDepartment of Earth and Planetary Physics, Graduate School of Science, The University of Tokyo, Tokyo, 113 Japan.
authors.forename: Masazumi
authors.initials: M
authors.lastname: Arai
authors.forename: Toshio
authors.initials: T
authors.lastname: Yamagata