Statistical Analysis of Banded Chorus Spectral Features Using Van Allen Probes and Arase Data: Implication for Power Gap Formation

Abstract

Magnetospheric chorus waves often accompany a gap in intensity near half of the electron cyclotron frequency, , whose generation process is still debated. One mechanism involving a nonlinear damping process proposed by Omura et al. (2009, https://doi.org/10.1029/2009ja014206 ) predicts a characteristic spectral signature where the lower cutoff of upper band waves, , follows local . Here, we statistically analyze spectral features of banded chorus waves from the Van Allen Probes and Arase spacecraft. Observationally, is almost one‐to‐one correlated with up to magnetic latitude for the banded chorus events in the midnight‐to‐dawn sector, but becomes nearly independent of for the events found on the dayside. By contrast, the upper cutoff of lower band waves, , depends only weakly on magnetic latitude and remains at approximately (where is the equatorial ) near the equatorial region, meaning that the power gap should have been already formed there. These results indicate that while the good correlation between and lends strong support for the nonlinear damping mechanism as a power gap enhancer during poleward propagation of chorus waves, its formation near the equatorial source region and/or on the dayside likely needs more concrete explanation.