Effects of low frequency waves and spiky electric fields in the magnetotail

Intense low frequency waves and large amplitude spiky electric fields are commonly observed in the active magnetotail. These fields are of dynamic significance for substorms because the waves are large enough amplitude to provide the dissipation necessary for reconnection to occur. In addition, the waves dramatically modify the trajectories of ions in the magnetotail, resulting in enhanced energization and pitch angle scattering in comparison to trajectories obtained without waves. The spikes may represent the nonlinear evolution of the waves. In this paper, we present observations of both low frequency waves and spiky electric fields measured by the double probe electric field instrument on the Geotail satellite within the plasma sheet. The relationship between the waves and the spikes is compared to theories of wave evolution. We present an evaluation of the Lundquist number, S, for the magnetotail based on the wave observations and previously published studies of current sheet scale sizes, utilizing the quasilinear expression for the anomalous resistivity from lower hybrid drift waves. For typical parameters, S varies from a few tenths to ten in the near earth plasma sheet and from a few tenths to fifty in the deep tail. The effects of the waves on ion trajectories are also discussed using the results from a particle tracing code.