Ionospheric ion cyclotron wave generation inferred from coordinated Doppler radar, optical, and magnetic observations

Doppler spectra obtained with two cross-beamed 50-MHz CW radio systems often showed narrow peaks near the gyrofrequencies of the principal ions in the E region (N2+, NO+, O2+, O+). Such peaks strongly suggest the existence of electrostatic ion cyclotron waves during auroral conditions. At times when strong ion cyclotron peaks were observed by the radar, all-sky pictures of the scattering region showed rays and coronas. Identification of the rays was made much easier because the upper portions of the rays were sunlit, so the resonance excitation of N2+ ions gave greatly enhanced 4278-A emissions that could be readily observed by the meridian-scanning photometer. This intimate association of the echoes with extended ray structures suggests that the echoes may have come from the upper E region, where the conditions for exciting the ion cyclotron instability by the field-aligned currents associated with the rays would be more favorable. There was a good correlation between the occurrence of the ion cyclotron type spectra and the E-W magnetic perturbation, which also may have been indicative of field-aligned currents. Finally, a close relationship was found between average plasma drifts inferred from the radar Doppler spectra and north-south motions of optical auroral forms.