FAST Observations of inertial alfvén waves and electron acceleration in the dayside aurora

Abstract

A prevailing feature of small scale (k_⊥ c/ω_pe ∼≥1) Alfven waves observed from the FAST spacecraft is an association of the impulsive wavefield with bursts of field-aligned electrons with energies of the order of $\text{1}\text{2}$m_eV²_A. The accelerated distributions have broad energy spectra up to a few 100 eV and are predominantly directed downwards although upward accelerated beams are sometimes observed. Observations show that the direction of acceleration is correlated with the direction of the wave Poynting flux and anti-correlated with the direction of the field-aligned current carried by the wave. The accelerated portion of the distribution in some cases carries all the field-aligned current since the thermal population is depleted. These observations are compared with the predictions of a 1-D MHD model (with an inertial correction) (Chaston, 2000) and a fluid-kinetic model (Clark and Seyler, 1999) for waveforms where k_⊥ c/ω_pe ∼1 and k_⊥ c/ω_pe>>1 respectively.