Particle dynamics in the Earth's magnetospheric tail

Abstract

In this paper, we will review basic particle motion in current sheets. The current sheet in the Earth's magnetospheric tail is but one example of naturally occurring current sheets. Other examples include: the heliospheric current sheet in the solar wind; solar flare and prominence ejection current sheets; the Earth's dayside magnetopause current sheet; Jupiter's magnetodisk; pulsar and galactic current sheets. For small, nearly constant normal magnetic field, Bz, particles oscillate about the current sheet and "live" within the sheet for one-half gyroperiod about Bz. This lifetime replaces the mean collision time in the Lorentzian electric conductivity expression, and thus gives rise to the concept of an inertial conductivity. A terrestrial magnetospheric substorm model by Coroniti (1985) utilizes this inertial conductivity to allow reconnection to proceed without anomalous processes. Chaotic particle orbits may, at times, be important to the dynamics, depending on parameters such as particle energy, current sheet thickness, and field line curvature. A current sheet model with a neutral line predicts a ridge structure and asymmetries in the distribution function. Some recent observations of ion distributions from the ISEE and AMPTE satellites are consistent with predictions of the model. Some remaining problems will be outlined.