Radio Bursts and Solar Energetic Particle Events
Abstract
Radio bursts in the solar atmosphere and interplanetary space come from energetic non-maxwellian electron populations. Since the radio emission is a non collisional process, it traces electrons also in dilute plasmas, where hard X-rays and gamma-rays are undetectable. Radio waves are therefore a probe of energetic electrons from the low corona to the interplanetary medium. This review outlines how radio signatures can be used to infer acceleration sites in flares and to visualize the magnetic structures which guide particles from the low corona to interplanetary space. Electron acceleration at coronal shock waves is then discussed. These are seen to accelerate less electrons than the impulsive acceleration processes operating in the low corona. The ability to determine onset times of SEP events to within a few minutes has recently revived the comparison with radio bursts as tracers of acceleration processes in the corona. Remarkable discrepancies in the timing of the escaping and interacting particles were ascribed to different acceleration processes of these particle populations (i.e. CME shock acceleration of the escaping particles), transport processes (delayed particle transport in interplanetary space) or a combination of time-extended acceleration in the magnetically stressed corona and transport to space along several diverging magnetic flux tubes. The different interpretations are confronted and discussed. It is concluded that particle acceleration at the Sun is not adequately described by a bimodal picture of "flare acceleration" of very short duration in very small volumes on the one hand and CME shock acceleration over large volumes on the other hand.
- Publication:
-
Geophysical Monograph Series
- Pub Date:
- October 2006
- DOI:
- 10.1029/165GM22
- Bibcode:
- 2006GMS...165..233K