Shock Formation, Energetic Particle Release, and Kinematics of Coronal Mass Ejections
Abstract
There are many source and environmental parameters that affect the characteristics of large solar energetic particle (SEP) events. We report on three primary characteristics that seem to determine whether a CME-driven shock can accelerate particles to very high energies. The first one is the height of shock formation, as indicated by type II radio bursts. For SEP events with GeV particles, the shocks form very close to the Sun, about half a solar radius above the solar surface. For events from filament eruptions (FEs) outside active regions, the shock forms at much larger heights - either in the outer corona or in the interplanetary medium. The second characteristic is the acceleration profile of CMEs. In high-energy particle events, the associated CMEs accelerate impulsively (initial acceleration is 2 km/s/s), ensuring strong shocks very close to the solar surface where the ambient magnetic field is high. In FE SEP events, the acceleration is typically an order of magnitude smaller, consistent with shock formation at large distances from the Sun. The third factor is the Alfven speed profile in the ambient medium. It is well known that the Alfven speed (or magnetosonic speed) in the corona increases from 300 km/s in the region where shocks typically form to several hundred km/s around 3 solar radii. After that the characteristic speed steadily declines. The behavior of the CME speed profile with respect to the Alfven speed profile essentially determines the true strength of the shock. One of the observational consequences of these three factors is the 10-100 MeV spectral index of the SEP events. We show that the high-energy SEP events and FE SEP events fall on the opposite ends of the distribution of the spectral index: 2 and >4, respectively.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMSH32A..06G
- Keywords:
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- 7509 Corona;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7513 Coronal mass ejections;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7514 Energetic particles;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7524 Magnetic fields;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY