Electron Dynamics Within Dispersive Scale Alfvénic Field-Line Resonances Embedded Within Substorm Auroral Beads

Abstract

Recent Cluster satellite observations have illustrated that substorm auroral bead formation and currents are associated with the presence of dispersive scale standing Alfvén waves, which are also known as kinetic scale field line resonances (KFLRs) or kinetic Alfvén eigenmodes. In this work, the properties of these waves are further examined using simulations of a gyrofluid-kinetic electron model in conjunction with the Cluster observations at mid-latitudes and Defense Meteorological Satellite Program satellite observations at high-latitudes. These simulations incorporate, for the first time, the effects of both hot magnetospheric and cold ionospheric electron populations within the multi-period evolution of KFLRs. The simulation results demonstrate consistent characteristics with the observed energized electron distributions both at mid- and high-latitudes. Tracing of the energized particle evolution shows that electrons can effectively interact with the wave all along the field line. Quantified energy conversion rates (as determined from $j_{\Vert }{E}_{\Vert }$) show that significant wave energy dissipation occurs at all latitudes with a maximum occurring in the vicinity of the peak in the profile of the magnetic field to density ratio $\left(B/n\right)$. Additionally, even though dispersive effects lead to the propagation of wave energy across field lines, the particle energization leads to rapid damping of the resonant system in only a few Alfvén periods.