Ion effects on ionospheric electron resonance phenomena

Abstract

Ion effects are often observed on topside‐sounder‐stimulated electron plasma wave phenomena. A commonly observed effect is a spur, appearing after a time delay corresponding to the proton gyroperiod, attached to the low frequency side of an electron plasma resonance. The spurs are often observed on the resonances at the electron plasma frequency, fN, the harmonics nfH of the electron cyclotron frequency fH (n = 2, 3, 4, ···), and occasionally on the upper hybrid frequency (fN2 + fH2)1/2. The spurs on the fN resonance are usually quite small unless the fN resonance overlaps with an nfH resonance; very large spurs are observed during such overlap conditions. Proton spurs are only observed on the nfH resonances when the electron plasma waves associated with these resonances are susceptible to the Harris instability and when the electromagnetic z wave can be initiated by the sounder pulse. This instability is the result of a sounder‐stimulated anisotropic electron velocity distribution. The observations suggest that energy is fed into the nfH longitudinal plasma wave from the z wave by means of wave‐mode coupling.