Simulation study of linearly polarized EMIC waves

Abstract:

Recent wave simulations and numerical calculations showed that resonant absorption at the ion-ion hybrid (IIH) resonance occurs in multi-ion plasmas at Earth and Mercury. The IIH resonance is believed to have an important role for electromagnetic ion cyclotron wave generation near the equatorial region in both planets. However, previous studies did not consider the electron inertial effects although the waves interact with electron and ions in such small spatial scale. They also considered magnetic compressional component near the IIH resonance are negligible, which is inconsistent with the recently observed EMIC waves with strong magnetic compressional component at Earth [1] and Mercury [2]. By adopting a time-dependent multi-fluid wave model that can fully include effects of electrons and multi-ions, we show how resonant absorptions occur in electron-proton-helium/oxygen plasmas when electron inertial effect is considered. Our results show that (a) resonant absorption occurs at both IIH and Bushsbaum (BB) resonances, (b) IIH resonant waves are electromagnetic with large wavelength while BB resonance has a strong electrostatic component with a small wavelength, and (c) the magnetic compressional component can be strong as the magnetic azimuthal component near the IIH resonance.

[1] Engebretson et al (2014). Purely Compressional Pc1 waves observed by the Van Allen Probes. abstract, AGU Chapman conference on Low-Frequency Waves in Space Plasmas.

[2] Boardsen et al. (2012). Survey of coherent ~1 Hz waves in Mercury's inner magnetosphere. From MESSENGER observations, J. Geophys. Res. 117, A00M05.