Io-jupiter interaction: Waves generated by pickup ions

Abstract

Abstract Ion pickup processes invariably produce anisotropic ion distributions and hence can give rise to wave generation. This paper discusses the waves due to the Io pickup source in Jupiter's magnetosphere. In the near-Io torus, the Galileo spacecraft observed ion cyclotron waves near the sulfur dioxide gyrofrequency, which grow due to the absence of a thermalized background component of these molecular ions in a torus plasma of predominantly dissociated species. These wave observations allow limits on pickup source rates to be estimated. On the edge of the Io wake, mirror mode waves were seen where the pickup ion contribution to the pressure anisotropy is sufficient to overcome the instability threshold. The mirror mode can dominate over the individual ion cyclotron modes in a multi-species plasma. The mass density in the torus cannot increase indefinitely and the plasma must be radially transported through the Jovian magnetosphere. Wave processes may be associated with any ion distribution anisotropies that arise during their radial transport, and with unsteady reconnection processes that may facilitate their eventual loss from the magnetotail.