A Study of Wave Expansion in the ion-Electron two-Fluid Plasma and the Formation of Frequency gap at Half the Electron Cyclotron Frequency

Abstract:

Chorus waves are commonly observed in the inner magnetosphere. The chorus waves are electromagnetic waves with frequency less than the electron cyclotron frequency but greater than the ion cyclotron frequency. The most noticeable feature of the chorus wave is the frequency gap at half the electron cyclotron frequency. However, chorus waves without a gap have also been observed. In this study, we examine the wave expansion in the ion-electron two-fluid plasma. Our results can explain the wave characteristics of the observed rising-tone waves and the falling-tone waves. Especially, our results can successfully explain the frequency gap based on the group-velocity distribution of the quasi-electromagnetic waves in the ion-electron two-fluid plasma.