  The core of a terrestrial-type planet consists of a spherical shell of
rapidly rotating, electrically conducting, fluid. Such a body supports two
distinct classes of quasi-geostrophic eigenmodes: fast, primarily hydrodynamic,
inertial modes with period related to the rotation time scale and slow,
primarily magnetic, magnetostrophic modes with much longer periods. Here, we
investigate the properties of these hydromagnetic quasi-geostrophic modes as a
function of non-dimensional parameters controlling the strength of the
background magnetic field, the planetary rotation rate, and the amount of
magnetic dissipation. ... read full length abstract in the paper.
