A finite element model for wave propagation and dissipation in space plasmas

Abstract:

Our ability to understand and model wave-particle interactions in the magnetosphere requires improved knowledge of the spatial distribution and properties of waves as well as improved understanding of how the waves depend on changes in solar wind forcing and/or geomagnetic activity. We have developed a two-dimensional, finite element code that solves the full wave equations in global magnetospheric geometry. The code describes three-dimensional wave structure including mode conversion when ULF, EMIC, and magnetosonic waves are launched in a two-dimensional axisymmetric background plasma with general magnetic field topology. We illustrate the capabilities of the code by examining the wave structure for EMIC waves in the inner magnetosphere. We first examine EMIC waves launched along the magnetic field from the equatorial magnetosphere, where EMIC waves are typically generated by ion temperature anisotropy. We examine the role of mode conversion, tunneling, and dissipation as the wave propagates toward the ionosphere. We discuss where the waves dissipate their energy, how the dissipation depends on the concentration of heavy ions, and whether detection of EMIC waves in the ionosphere places constraints on heavy ion concentrations. We also examine how externally generated compressional waves (launched across the magnetic field) mode convert at the ion-ion hybrid resonance, and whether these mode converted waves could explain observations of linearly polarized waves in the dawnside magnetosphere.