Rotating multipoles on the f- and γ-planes

Abstract

A family of semianalytical solutions is presented describing multipolar vortical structures with zero total circulation in a variety of two-dimensional models. Analytics are used to determine the form of a multipole edge, or separatrix, and the solution outside this separatrix. The interior is solved using a Newton-Kantorovich (successive linearization) procedure combined with a collocation method. The models considered are the quasigeostrophic f- and γ-planes, with either the rigid-lid or free-surface conditions. A multipole, termed also an (m+1)-pole, is a vortical system that possesses an m-fold symmetry (m≥2) and is comprised of a central core vortex and m satellite vortices surrounding the core. Fluid parcels in the core and the satellites revolve oppositely, and the multipole as a whole rotates steadily. The characteristics of the multipoles are examined as functions of m and a parameter that incorporates the Rossby deformation radius, γ-effect, and the vortex’s angular velocity. The analogy between the β-plane modons and γ-plane multipoles is tracked.