Harmonic Ion Cyclotron Resonances observed by the OGO–4 Satellite

Abstract

A NEW very low frequency phenomenon associated with the propagation of whistlers in the upper ionosphere has recently been found in the VLF recordings from the Injun 3 and Alouette satellites¹. This phenomenon showed up on a frequency–time spectrogram as a rising tone which started immediately after the reception of a short fractional-hop whistler. The spectrogram showed a rapid rise in frequency with an asymptotic approach to the cyclotron frequency for the protons in the plasma surrounding the satellite. These signals have been called proton whistlers. Analysis has shown that they are excited because of mode coupling or conversion from the electron whistler mode with right-hand polarization to the ion cyclotron wave with left-hand polarization². The frequency at which polarization reversal or coupling occurs has been called the crossover frequency, which is below the ion cyclotron frequency. More recently it was reported that the ion wave at a helium cyclotron frequency has been observed in addition to the proton whistler in one of the Alouette II records³.