Kinetic simulations of electron response to shear Alfvén waves in magnetospheric plasmas

Abstract

Standing and traveling shear Alfvén waves contribute to electron acceleration and parallel electric field formation on auroral field lines in the Earth’s magnetosphere. In this paper, the self-consistent coupled Vlasov–Maxwell system for shear Alfvén waves is solved in one dimension. The Vlasov equation is gyro-averaged in order to minimize the number of dimensions in the problem, and to avoid numerical problems with the direct evaluation of the parallel electric field, the electron distribution function is described in terms of a spatial coordinate along the field line, the magnetic moment, and the canonical parallel momentum per unit mass. Some preliminary studies of shear Alfvén wave pulses propagating in a uniform magnetic field on model auroral field lines are presented with an emphasis on the kinetic electron response and the parallel electric field. It is shown that when the full parallel electron dynamics are included, wave–particle interactions result in intensification of the parallel electric field and significant heating of the electrons. It is also demonstrated the acceleration of electrons to speeds of the order of twice the wave phase speed, which has been shown by previous calculations. The results are compared with recent observations made by both the NASA Fast Auroral Snapshot and the Freja satellites.