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Coronal sources of solar energetic particle events



The present picture of acceleration processes leading to solar energetic particle (SEP) events distinguishes two sources in the solar corona: flares are considered as generators of SEP events that are detected when the satellite is well connected with the site of the H alpha signature, and large scale shocks driven by fast coronal mass ejections (CMEs) are believed to accelerate particles over a large range of heliocentric angles out of the coronal plasma, leading to the largest and longest lasting SEP events. While such a neat separation of accelerators is able to account for observed properties such as the appparently bimodal distribution of ionization states (especially Fe) and of abundance peculiarities at energies up to a few MeV per nucleon, it also involves unproven assumptions: - that a single accelerator acts at all energies, from suprathermal   to relativistic, - that flare-related acceleration operates only in a small volume and during  negligibly short duration with respect to the SEP event.

The present contribution attempts to review observational constraints by comparing the time history of coronal particle acceleration with that of protons and electrons detected between 0.3 and 1 AU. It is pointed out that during the combined occurrence of CMEs and flares electrons may be accelerated at, or transported to widely separated sites behind the CME, and that there is some evidence on the co-evolution of these electron signatures and energetic electrons and protons (>> 1 MeV/nucleon) detected in interplanetary space. This suggests that a more complex scenario of coronal particle acceleration may be required to understand SEP events than the distinction of flare accelerated and shock accelerated particle populations.

Above is background material for archival reference only.

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NASA Official: Adam Szabo

Curators: Robert Candey, Alex Young, Tamara Kovalick

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