Fast Auroral Snapshot observations of cusp electron and ion structures

The high time resolution observations by the Fast Auroral Snapshot satellit e 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 pa ttern. The large-scale DC electric field variations are well correlated wit h the large-scale perturbation magnetic field, indicating a field-aligned c urrent system that reflects a relatively homogenous conductivity. Ion struc tures 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 Alfven waves. We also found that the observed ion structures result from the spacecraft crossing the flow streamlines, each of which ha s its own individual history of dayside reconnection. The magnetosheath ion structures therefore contain information of both the spatial and temporal variations of dayside reconnection.