Coronal Mass Ejections and Ground Level Enhancement Events
Abstract
Ground level enhancement (GLE) in solar energetic particle (SEP) events represent the production of GeV particles by the Sun during large solar eruptions. Although the GLE events were first detected in 1942 and reported by Scott Forbush (1946) a few years later, the mechanism for the production of these high-energy particles is not fully understood. GLEs were attributed to solar flares from the beginning, but after the discovery of coronal mass ejections (CMEs) in 1971, the possibility of CME-driven shocks accelerating GLE particles has also gained importance. Extensive CME observations in association with GLEs became available only during solar cycle 23, enabling a fresh look at the importance of CME-driven shocks. This paper presents a summary of CME properties obtained primarily from the Solar and Heliospheric Observatory (SOHO), which are fully consistent with shock acceleration of GLE particles. During solar cycle 24, there has been only one GLE event (on May 17, 2012) as of this writing. This is the first GLE event to be fully observed by the Solar Terrestrial Relations Observatory (STEREO) mission, providing critical information on CME kinematics that helped verify the results obtained for cycle 23 GLE events. In particular, it is confirmed that (i) the shock forms very close to the solar surface (within half a solar radius) and the GLE particles are released ~10 minutes later, and (ii) GLE events require special conditions in terms of CME kinematics, coronal environment, and the magnetic connectivity of the solar source to an Earth observer. Forbush, S. E., Three Unusual Cosmic-Ray Increases Possibly Due to Charged Particles from the Sun, Physical Review, 70, 771, 1946
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSMSH33B..04G
- Keywords:
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- 7513 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Coronal mass ejections;
- 7514 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Energetic particles;
- 7519 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Flares;
- 7534 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Radio emissions