Distinguishing the Rigidity Dependences of Acceleration and Transport in Solar Energetic Particles
Abstract
In solar energetic particle (SEP) events, the power-law dependence of element abundance enhancements on their mass-to-charge ratios [A /Q ] provides a new tool that measures the combined rigidity dependences from both acceleration and transport. Distinguishing between these two processes can be challenging. However, the effects of acceleration dominate when SEP events are small or when the ions propagate scatter-free, and transport can dominate the temporal time evolution of large events with streaming-limited intensities. Magnetic reconnection in solar jets produces positive powers of A /Q from +2 to +7 and shock acceleration produces mostly negative powers from −2 to +1 in small and moderate SEP events where transport effects are minimal. This variation in the rigidity dependence of shock acceleration may reflect the non-planar structure, complexity, and temporal time variation of coronal shocks themselves. Wave amplification by streaming protons in the largest SEP events suppresses the escape of ions with low A /Q , creating observed powers of A /Q from +1 to +3 upstream of the accelerating shock, decreasing to small negative powers downstream. For shock acceleration, the powers of A /Q are correlated with the energy spectral indices of He, O, and Fe, yet unexplained departures exist.
- Publication:
-
Solar Physics
- Pub Date:
- August 2020
- DOI:
- 10.1007/s11207-020-01680-6
- arXiv:
- arXiv:2006.11338
- Bibcode:
- 2020SoPh..295..113R
- Keywords:
-
- Solar energetic particles;
- Solar system abundances;
- Coronal mass ejections;
- Shock acceleration;
- Astrophysics - Solar and Stellar Astrophysics;
- Physics - Space Physics
- E-Print:
- 25 pages, 13 figure, submitted to Solar Physics