Case studies of ion energisation events near substorm onset

In a recent one-dimensional self-consistent hybrid code simulation of the local dipolarisation of the initially distended magnetic field in the near-earth nightside region, (Richardson and Chapman, 1994), initially isotropic ions were accelerated up to twice the Alfven speed along the direction of the magnetic field. A bistreaming ion population was generated in the weak field region at the centre of the reversing field, and monostreaming ions were found to move away from the region of dipolarisation. Moreover, a bipolar signature in the cross tail component of the field and fast magnetosonic waves propagating away from the reversal region are predicted by the simulation. We test these predictions by examining particle and magnetic field data from the Low Energy Plasma Analyser (LEPA) experiment and fluxgate magnetometer instrument onboard the Combined Release and Radiation Effects Satellite (CRRES). We examine a set of events that were found to be consistent with some of the features of the simulation results.