The physics in the auroral dynamo regions and auroral particle acceleration

Abstract

Auroral particle acceleration requires an energy flux flowing into the acceleration region and the subsequent development of parallel electric fields. Auroral arcs are often very dynamic, and even in cases when a quasi-steady arc is formed, the question arises of how the system evolved to this quasi-steady state. Existing theories of auroral current generation and the formation of parallel electric fields mostly consider such a steady situation, limiting their ability to describe the dynamics of the system. Since the energy necessary to power auroral particle acceleration is related to the auroral current system, the generation of field-aligned currents (FAC) and auroral particle acceleration are closely coupled. Thus, in order to understand the dynamics of auroral particle acceleration, the physics in the auroral dynamo region must also be considered. Construction of such a dynamical theory of the auroral current system requires that the time-dependent generation of field-aligned currents (∂J|/∂t) and the dynamics of the generation of parallel electric fields (∂E|/∂t) and parallel potential drops must be the primary considerations.The time-dependent generation of FAC filaments can occur as a result of the interaction of the MHD fast mode wave packets and a current sheet, either at the magnetopause or in the plasma sheet. In this process, a shear Alfvén wave can be generated in a discrete form as shear Alfvén wave packets. Although a single shear Alfvén wave packet can propagate without distortion or nonlinear interaction, the interaction of incident and reflected shear mode wave packets in the auroral acceleration region can release the kinetic and/or magnetic energy carried by the wave packets. Either solitary waves accompanied by a charge condensation (charge hole) or a net parallel potential drop may be formed, depending on the polarizations of the interacting wave packets. In order to produce FAC filaments and parallel electric fields by the wave packet interaction, a localized breakdown of the frozen-in condition is necessary. The electron inertial term is a natural candidate to break the frozen-in condition locally.