Nonlinear Dynamics and Auroral Acceleration Processes of Electrons Driven by Kinetic Alfvén Waves in the Magnetosphere

Abstract

This study investigates the nonlinear Landau resonance and auroral acceleration processes of electrons driven by kinetic Alfvén waves (KAWs) in the Earth's magnetosphere. We analyze electron trajectories and parameters, such as kinetic energy, using test particle simulations, focusing on the transition between phase-trapped and phase-scattered states induced by magnetic field gradients. Based on the second-order resonance theory, we define the conditions under which electrons are either trapped or non-trapped by the KAWs. Our key findings are: (a) Electrons can be significantly accelerated not only when they are trapped by the waves and transported toward the ionosphere, but also in the detrapped state; (b) Even with monochromatic KAWs, the energy of electrons in the ionosphere depends on their state at the moment they are detrapped from the KAWs; (c) The dynamics of phase-scattered electrons affect the efficiency of electron acceleration processes.