Particle energization by oblique inertial Alfvén waves in the auroral region



[1] Two-and three-dimensional electromagnetic particle-in-cell simulations are performed to study the particle energization by oblique inertial Alfvén waves in the auroral region. It is found that most of the wave energy is transferred to the parallel acceleration of electrons and transverse acceleration of ions (TAI) as the result of nonlinear evolution of an initial wave. The wave-particle interactions between the Alfvén wave and the electrons form a field-aligned electron beam, which is consistent with the time-dispersive electron signature and the suprathermal electron bursts observed by spacecraft. The steepening and subsequent breaking evolution of the Alfvén wave generates a combination of ion cyclotron and ion acoustic waves which, in turn, heats the ions transversely. The parallel-accelerated electron beam could result in ion cyclotron and ion acoustic instability, but it is generally too weak to be the wave generation mechanism. Three-dimensional simulations suggest that the sheared field-aligned current sheet embedded in a transversely finite Alfvén wave is subject to current shear-driven (CSD) instabilities. It is very possible that the ion cyclotron and ion acoustic waves generated by the wave breaking process, as well as the low-frequency electromagnetic fluctuations generated by CSD instabilities, are present in observed broadband ELF fluctuations and contribute to the associated TAI.