Dynamics of auroral particle acceleration by kinetic Alfvén waves

English Abstract:

It is now generally believed that there are at least two forms of auroral particle acceleration: a nearly monoenergetic acceleration through quasi-static parallel electric fields, and a broad-band acceleration associated with the propagation of kinetic Alfvén waves along auroral field lines. This Alfvénic acceleration also takes on two forms. In the low-β region at low altitudes, the electrons can be accelerated in bulk by the parallel electric field. At higher altitudes, where the plasma β is larger than the electron-to-ion mass ratio, electrons can be accelerated due to a Landau damping process. Furthermore, the precipitation of electrons due to Alfvénic acceleration leads to conductivity enhancements in the ionosphere, which can provide a positive feedback in structuring auroral currents. In addition, the production of secondary and backscattered electrons modifies the structure of the auroral flux tube and can set up conditions conducive to the formation of plasma double layers. These interactions will be illustrated through numerical simulations of the interaction of kinetic Alfvén waves with the auroral ionosphere.