Examining Wave Vector and Minimum Cyclotron Resonant Electron Energy of EMIC Waves With Magnetospheric Multiscale Mission

Wave number vectors k and minimum cyclotron resonant electron energies E min of electromagnetic ion cyclotron (EMIC) waves are analyzed via the phase differencing technique by using Magnetospheric Multiscale Mission data. It is demonstrated that the phase differencing method provides an estimate of the dominant wave number when finite k spectrum broadenings occur. A case study is conducted for the EMIC event on 20 November 2015, showing remarkable agreements with spectral analysis in wave propagation directions. We find that obtained wave vectors, roughly agreeing with the validity of cold plasma theory, might significantly vary from wave packet to wave packet. Numerical calculations indicate that E min can range from 0.5 to tens of MeV, suggesting that EMIC waves can effectively interact with those relativistic electrons. This study enriches our understanding of the applicability of phase differencing. It further supports that EMIC waves can be responsible for the loss of electrons with an extremely broad energy range in the magnetosphere.