Properties of small‐scale Alfvén waves and accelerated electrons from FAST

The FAST spacecraft observes Alfvénic fluctuations in field quantities throughout the auroral oval. In this report, we show preliminary results from a statistical study of Alfvén waves with transverse scales comparable to the electron skin‐depth observed over the frequency range from 0.2 to ∼20 Hz in the spacecraft frame. This study shows that these waves are most commonly found in the magnetospheric cusps and at the polar cap boundary of the auroral oval in the premidnight sector where the most intense events are observed. It is shown that the wave Poynting flux is well correlated with the energy flux of field‐aligned upgoing and downgoing electrons. It is also shown that over the FAST altitude range (350–4175 km), the wave Poynting flux decreases with decreasing altitude, most likely due to losses through electron acceleration. It is demonstrated, however, through the use of simulations and observations that most of the electron acceleration occurs at altitudes above FAST between 1 and 2 Earth radii ( R E ), with the most energetic electrons arriving from an altitude of ∼2–3 R E for statistically determined density and composition profiles.