Nonlinear dispersive scale Alfvén waves inmagnetosphere-ionosphere coupling: Physical processes and simulation results

Abstract

Dispersive Alfven waves (DAWs) have been demonstrated to play a significant role in auroral generation of the magnetosphere-ionosphere coupling system. Starting from a two fluid reduced MHD model, we summarize the frequency, temporal and spatial characteristics of magnetospheric DAWs. Then, the nonlinear kinetic and inertial scale Alfven waves are studied, and we review some theoretical aspects and simulation results of dispersive Alfven waves in Earth’s magnetosphere. It is shown that dispersive standing Alfven waves can generate the field-aligned currents which transport energy into the auroral ionosphere, where it is dissipated by Joule heating and energy lost due to electron precipitation. The Joule dissipation can heat the ionospheric electron and produce changes in the ionospheric Pedersen conductivity. As a feedback, the conducting ionosphere can also strongly affect the magnetospheric currents. The ponderomotive force can cause the plasma to move along the field line, and generate ionospheric density cavity. The nonlinear structuring can lead to a dispersive scale to accelerate auroral particle, and the Alfven waves can be trapped within the density cavity. Finally, we show the nonlinear decay of dispersive Alfven waves related to two anti-propagating electron fluxes observed in the auroral zone.