Alfvén Wave Parallel Electric Field in the Dipole Model of the Magnetosphere: Gyrokinetic Treatment

A mechanism for generation of the parallel electric field by Alfvén wave in the dipole model of the magnetosphere in full gyrokinetics is proposed. The parallel electric field of the Alfvén mode is caused by the coupling of the Alfvén and electrostatic modes due to the plasma inhomogeneity and field line curvature in presence of the trapped hot electrons. The parallel electric field is described by an inhomogeneous integral equation arising from the averaging of the bounce motion of hot electrons. It was found that the parallel electric field is localized near the ionosphere at the heights below 0.5 Earth's radius. For typical Alfvén wave amplitudes observed in space, the parallel electric field potential reaches the values of several kV, which can provide enough acceleration for the precipitating auroral electrons. Plain Language Summary Some of the auroras are observed simultaneously with the Alfvén waves, and the variation of auroras luminosity may correlate with the phase of the Alfvén wave. Many mechanisms explain this phenomenon, but none fully satisfy all the observed facts. This article proposes a mechanism for generating the parallel electric field by an Alfvén wave in a single framework without using hybrid models, which helps to better understand the physics of the process. Also, the proposed mechanism describes well the acceleration of electrons to the observed energies. Key Points The Alfvén wave generates a parallel electric field due to the presence of hot electrons The Alfvén wave parallel electric field is localized at a height about one Earth's radius The Alfvén wave parallel electric field can be values of several kV