Fast Auroral Snapshot observations of cusp electron and ion structures

Abstract

The high time resolution observations by the Fast Auroral Snapshot satellite resolve burst‐like electrons and nonmonotonic ion dispersion in the cusp region. Electric field data from a dawn‐dusk cusp crossing show that the DC electric field has small‐scale variations superimposed on a large‐scale pattern. The large‐scale DC electric field variations are well correlated with the large‐scale perturbation magnetic field, indicating a field‐aligned current system that reflects a relatively homogenous conductivity. Ion structures best correlate with the perturbed magnetic field and the large‐scale electric field. The burst‐like precipitating electrons are correlated with the small‐scale electric field variations, which are most easily explained as propagating Alfvén waves. We also found that the observed ion structures result from the spacecraft crossing the flow streamlines, each of which has its own individual history of dayside reconnection. The magnetosheath ion structures therefore contain information of both the spatial and temporal variations of dayside reconnection.