Resonant absorption of ULF waves near the ion cyclotron frequency: A simulation study

Abstract

We present a numerical investigation of Alfven resonances when frequencies are comparable to the ion cyclotron frequency(ωci) and MHD approximations become no longer valid. We have developed a three‐dimensional multi‐fluid wave model, which can fully include the effects of multi‐ions and electron. We use simple box model of an inhomogeneous plasma to examine how wave coupling properties change when the characteristic MHD resonance modes become comparable to ωci. The wave spectra and energy relations are presented for both MHD waves and ion cyclotron waves. Our results show that previous resonant absorption in pure MHD waves is well confirmed in the multi‐fluid model. By adopting a set of new eigenmodes, we show that the resonant absorption persists even for the higher frequency. It is suggested that, near ωci, the left‐handed circularly polarized mode is likely to behave as a shear mode in the MHD limit.