Non-axisymmetric shear layers in precessing fluid ellipsoidal shells

The motion of uid in a slowly precessing ellipsoidal shell is calculated numerically. A novel spectral method is employed which uses a decomposition in spherical harmonics but enforces boundary conditions on oblate surfaces. Internal shear layers appear in the simulated ows either because the ellipticities of inner and outer boundaries dier, or because Ekman layers break down. The structure of these layers and their orientation with respect to the axis of precession depends on the relative magnitudes of pressure and viscous torques exerted by the boundaries on the uid.