Baroclinic Modons on a Sphere

Abstract

Baroclinic modon solutions of the two-level quasigeostrophic vorticity equations on a sphere are presented. These modons with both barotropic and baroclinic components can be made stationary in a zonal background with vertical shear. The sphere is divided into an inner and outer region separated by a boundary circle. There are constraints on the wavenumbers of the solutions in the inner and outer region and on the radius of the circle. Then wavelike, semiwavelike, and localized solutions exist, with different relationships between potential vorticity and streamfunction for the two regions on the two levels. There is a maximum vertical shear of the zonal background for a modon solution with given wavenumbers similar to a marginality curve known from baroclinic instability theory. The solutions are dipoles accompanied by monopoles, but under additional constraints quad-rupoles exist. The solutions are compared with earlier results for barotropic modons on a sphere and baroclinic modons on a beta plane.