Radar observations of ion cyclotron waves associated with two barium shaped‐charge releases

Abstract

A 50‐MHz Doppler radar interferometer and a 138‐MHz Doppler radar were operated from Kennedy Space Center to study 3‐m and 1‐m plasma waves associated with two shaped‐charged barium releases from Wallops Island, Virginia, on May 13, 1986. During the first release, interferometer and Doppler power spectral studies showed the existence of short‐lived (<2 s) coherent 3‐m and 1‐m waves centered near 30 Hz. The 3‐m waves were located about 100 km above the release on a magnetic field line in contact with the first release. No radar backscatter was observed by the radars during the second release. The coherent 30‐Hz radar echoes associated with the first barium release are very similar to some natural occurring auroral radar echoes that are believed to be generated by resistive current‐driven electrostatic ion cyclotron waves. A detailed linear dispersion analysis of electrostatic ion cyclotron (EIC) waves showed that only 3‐m O+ EIC waves were unstable for field‐aligned electron drifts greater than 0.7υthe at the altitude of 510 km in a multispecies (O+, NO+, or similarly O2+) ionospheric plasma. We interpret the 30‐Hz waves seen by the two radars far above the release as strong electrostatic ion cyclotron waves generated by intense field‐aligned currents associated with the barium stream acting like an MHD generator coupled to the ionosphere.