1464-1917/00/ $- see front matter Accelerated Electrons as the Source of Auroral Kilometric Radiation

Abstract. Data from the Fast Auroral Snapshot Explorer (FAST) have confirmed that Auroral Kilometric Radiation (AKR) is generated by the accelerated electrons in the auroral density cavity. FAST observations of the electron distribution within the AKR source region show a characteristic horse-shoe distribution expected from the parallel electric field acceleration and magnetic mirroring of the electrons, the precipitating portion of which constitute the auroral electrons. Within the density cavity it is likely that the hot electrons carry most, if not all, of the plasma density. The AKR wave characteristics within the source region show that the lower frequency cut-off is below the cold electron gyro-frequency, and near the cut-off, the wave electric and magnetic field polarization is consistent with perpendicularly propagating X-mode waves. Taken together these observations are consistent with the cyclotron maser instability, but with the inclusion of relativistic effects in the wave dispersion, as well as the resonance condition. This allows the accelerated electrons to generate AKR, and further the replenishment of the distribution by the parallel electric field ensures that AKR can be generated over a large altitude range on auroral zon