Dispersive scale Alfven waves associated with broadband aurora: Results of 2-D gyrofluid-kinetic electron simulations

Abstract:

The formation of the broadband aurora (such as seen at substorm onset) is well correlated with Poynting flux associated with dispersive scale Alfven waves that may be generated as a result of reconnection- or instability-driven processes in the plasma sheet. Ion temperature effects are important in this context as the ion gyroradius is a fundamental scale-length for the transfer of global scale substorm energy to particle energization and since these effects modify the phase speed of the wave (which affects both substorm onset timing and electron acceleration). We present simulations of dispersive scale Alfven wave pulses using a new gyrofluid ion-kinetic electron model in curvilinear coordinates. We find that consideration of a realistic ion to electron temperature ratio significantly reduces the propagation time of the wave from the plasma sheet to the ionosphere (relative to the case that neglects ion temperature effects) and leads to an increased dispersion of wave energy perpendicular to the ambient magnetic field. Ion temperature effects also reduce the parallel current and parallel electric field within the wave and we elucidate the affects of this reduced coupling on the structure and evolution of the energized electron distribution functions for a range of plasma sheet wave parameters.