Wavenumber Analysis of EMIC Waves

It has been highly controversial as to whether and how efficient electromagnetic ion cyclotron (EMIC) waves can scatter sub-megaelectronvolt (MeV) to multi-megaelectron volt electrons into the atmospheric loss cone. The capability of EMIC wave scattering essentially depends on the wavenumber spectra, instead of readily available frequency spectra. We present a method to obtain the EMIC wavenumbers directly from the wave electromagnetic field measurements, from which we further evaluate the characteristics of electron minimum resonant energy and electron scattering rate due to EMIC waves. Based on the analysis of EMIC waves identified from 5.5 years of Van Allen Probes field measurement, we find that only a small fraction of H+ band wave events can resonate with electrons down to MeV, while none of He+ band waves at the maximum wave power can. The electron scattering rate increases with increasing levels of geomagnetic activities. The scattering rate for H+ band is sufficient to cause significant precipitation of electrons for a broad energy range (including MeV electrons), especially during times with high geomagnetic activity.