资源环境科技发展态势分析平台

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 Emin 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.

Plain Language Summary Electromagnetic ion cyclotron (EMIC) waves scattering relativistic electrons is an important mechanism for relativistic electron losses in radiation belts. The present paper studies the energy range of relativistic electrons that can interact with EMIC waves. The evaluation of the minimum resonant electron energy (typically >2 MeV) varies, depending on the dispersion relation used, which depends on rarely available ion composition and plasma environment. Here we use four Magnetospheric Multiscale spacecraft observations to directly calculate the wave vector of EMIC waves by phase differencing technique and subsequently estimate the minimum resonant energy. An interesting finding is that, even for quasi-monochromatic EMIC waves, there exists wave packets of very different wave number values, implying impulsive nature of the EMIC generation mechanism at the source region. The estimation of minimum resonant energies indicates that the EMIC waves can be in resonance with the electrons of energies from tens of MeV down to an unexpectedly low energy (similar to 0.5 MeV), which is in lack of directly observational evidences.