  The numerical simulations of planetary dynamos still operate in a regime very
far from the planets. For example, it seems unlikely that viscous forces are at
all significant in planetary interiors, yet some of the simulations display a
significant dependence on viscosity, and indeed in some of the simulations the
dynamo mechanism is itself viscously driven, taking the form of helical Ekman
pumping within columnar convection rolls. Given the similarity of the external
magnetic fields observed in the terrestrial planets and gas giants, and the
extremely small value of the Ekman number in all such cases, it seems natural
to suppose that the underlying dynamo mechanism in these planets is independent
of viscosity and insensitive to mechanical boundary conditions. A key step to
identifying this mechanism is to determine the source of helicity in planetary
cores. In this paper we explore the possibility that the helicity in the core
of the Earth arises from the spontaneous emission of inertial waves, driven by
the equatorial heat flux in the outer core.
