Course 7 Taylor's constraint and torsional oscillations

Abstract

Publisher Summary This chapter reviews the basic concepts behind Taylor's constraint and torsional oscillations. It discusses that Taylor's constraint is a morphological condition on the Earth's magnetic field inside the core. It specifies that the field must be organized such that the Lorentz torque integrated over cylindrical surfaces aligned with the rotation axis must vanish. A magnetic field obeying such a Taylor state was once viewed as the way to find solutions of the geodynamo problem and Taylor's constraint is important partly for this historical reason. Another reason for its importance is that torsional oscillations, which are azimuthal oscillations of rigid cylindrical surfaces in the core, are an essential physical ingredient to a Taylor state. These oscillations are believed to be observed in the secular variation of the magnetic field at the Earth's surface and in the changes in the length of day. The presence of torsional oscillations is important not only because they suggest that the Earth's core is in a Taylor state, but also because they provide a window through which we can observe other aspects of core dynamics.