A THEORETICAL AND EXPERIMENTAL STUDY OF THE MOTION AND STABILITY OF CERTAIN ATMOSPHERIC VORTICES

Abstract

This paper presents a description of experiments on the stability of a polar vortex and offers a theory for the experimental results. The experimental set-up is a rotating spherical shell, containing two immiscible liquids. The denser liquid covering the polar region is given a rotation with respect to the spherical shell, and observations are made to determine the tendency for the vortex to be displaced equatorward. The observations indicate that a cyclone centered near the pole is stable in the sense that its center of mass remains near the pole. An anticyclone tends to be unstable, however, so that its center of mass is displaced equatorward if its rotation is sufficiently strong. In connection with the experiments, the equations of motion of a simplified vortex were developed for a spherical earth. These are applied to obtain an instability criterion for a polar vortex. Other applications of these equations are described. One of these is a study of the motion of a vortex imbedded in a uniform vorticity field on earth. This reveals a tendency for all anticyclones and weak cyclones to move southward. This tendency is strongest at low latitudes. The initial motion of a vortex in an environment at rest with respect to the earth is also considered. The net force on the vortex is very close to one-half the Coriolis force due to the internal spin.