AlfvÉnic Accelerated Electrons And Short Burst Auroral Kilometric Radiations Observed By The Fast Satellite

Abstract

This investigation is motivated by previous study of short burst radiations (S-bursts) reported by Ergun et al. [2006], who suggested two generation mechanisms of S-bursts: one is the electron cyclotron maser instability due to an unstable ring distribution; the other is an upward electron beam generating upper hybrid resonance. The simulation results reported by Su et al. [2007] support the former mechanism. Only one Earth-based S-burst event was reported prior to our study. A systematic study was performed on particle and field observations from the FAST spacecraft to search for events of S-bursts and Alfvén waves. Eight events involving coexistence were identified and are presented in this thesis. All of them were observed at altitudes greater than 2500 km during winter months. In addition, S-bursts associated with Alfvénic perturbations were detected during periods when the AE indices were high, indicating a possible association with substorms. Furthermore, 24 dayside Alfvénic events and 20 nightside events were examined in detail. We found that the electron phase space density peaks along the magnetic field line for the nightside, which supports the concept of field-aligned acceleration by inertial Alfvén waves. However, the electron anisotropies involving the phase space densities peaked perpendicular to the magnetic field were observed on the dayside.