Hydromagnetic constraints on deep zonal flow in the giant planets

Abstract

The observed atmospheric zonal flows of the giant planets will, if they penetrate below the visible atmosphere, interact significantly with the planetary magnetic field outside the metallized core. The authors study this interaction by applying a simple model of the equatorial zonal jet in which the flow is assumed uniform on cylinders concentric with the spin axis, and viscous and magnetic torques on each cylinder are balanced. The authors solve this "Taylor constraint" simultaneously with the dynamo equation to obtain the velocity and magnetic field in the equatorial plane. This model reproduces the widely differing jet widths of Jupiter and Saturn (though not the flow at very high or low latitudes). A model Uranian jet consistent with the limited Voyager data can also be constructed.