Toroidal ion distributions observed at high altitudes equatorward of the cusp

Abstract

We examine events where the TIDE and TIMAS ion instruments on board the Polar spacecraft have observed transversely accelerated ions (TAI) at altitudes greater than 20,000 km. We report both H + and O + populations that have been heated perpendicular to the local B field but that also have a sharp low-energy cutoff to the distribution occurring at 20 - 100 eV. Analysis of an event on 21 April 1996 indicates that the formation of ion toroids may be related to solitary structures or low frequency wave pulses observed during the event. We address some of the implications of using time (as opposed to frequency) domain techniques to analyze wave/particle energization events.