THE ASSOCIATION OF ELECTROSTATIC ION-CYCLOTRON WAVES, ION AND ELECTRON-BEAMS AND FIELD-ALIGNED CURRENTS - FAST OBSERVATIONS OF AN AURORAL-ZONE CROSSING NEAR MIDNIGHT

FAST particle and wave data for a single nightside auroral zone crossi ng are utilized to examine the free energy source for electrostatic io n cyclotron (EIC) waves. Comparisons of the unstable wave modes, obtai ned by an electrostatic linear dispersion relation solver, to the obse rved waves for two intervals with upflowing ion beams and two with upf lowing electron beams are consistent with the conclusion that the obse rved waves near the cyclotron frequencies are EIC which are driven by the electron drift both in the upgoing ion beam regions and in the upg oing electron regions. A limitation is that the drifting bi-Maxwellian model used in the dispersion relation is not a good match to the obse rved upflowing electron distributions. The observed ion beams do not d rive EIC waves; however, the relative drift of the various ion species comprising the ion beam can drive low frequency (<similar to 50 Hz) w aves unstable. The electron drift, during some intervals, also destabi lizes electron acoustic waves.