The motion of near-Earth (10–15 R E) plasma sheet particles during substorms

Abstract

The dynamics of mid-tail ions during storm-time “dipolarization” of the magnetospheric field lines is investigated by means of time-dependent particle codes. The calculations yield two results of particular interest: (i) short-lived plasma injections into low f-shells under the effect of large transient electric fields, (ii) temporal non-adiabaticity in the near-Earth plasma sheet. Here, a boundary can be identified, delineating the adiabatic and nonadiabatic regimes of the particle orbits. In the nonadiabatic case, two sub-regimes can further be extricated, corresponding to distinct field rates of change per cyclotron turn: due to phasing with the surging electric field, one strongly depends upon gyration phase at substorm onset and can yield prominent damping of the particle magnetic moment. The other displays a much weaker phase dependence and intense perpendicular heating. These transport features may give rise to precipitation enhancements during storm times, due to either magnetic moment damping or impulsive parallel energization.