High‐order stimulated ionospheric diffuse plasma resonances: Significance for magnetospheric emissions

Abstract

The sequence nature of the diffuse ionospheric resonances Dn stimulated by topside sounders was discovered by Oya (1970) with n ranging from 1 to 4. Osherovich (1987) organized these observations using his earlier theory which predicted a nonequidistant spectrum with frequencies proportional to n1/2 where n = 1, 2, …. This work has since been used to predict the exact spectral position of naturally occurring magnetospheric emissions, and such emissions corresponding to n = 4 and 5 were identified in the IMP 6 data. These results motivated a search for the stimulated ionospheric counterpart at n = 5. We here present Alouette 2 and ISIS 1 topside sounder evidence for the stimulation of Dn resonances with n > 4. The results indicate the close relationship between active ionospheric plasma wave experiments and the interpretation of magnetospheric emissions.