Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc.1039..124d&link_type=abstract
PARTICLE ACCELERATION AND TRANSPORT IN THE HELIOSPHERE AND BEYOND: 7th Annual International Astrophysics Conference. AIP Confer
Astronomy and Astrophysics
Astrophysics
Astronomical Observations, Spectroscopy And Spectrophotometry, Flares, Magnetohydrodynamics And Plasmas, Abundances, Chemical Composition, Corona
Scientific paper
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged ~0.1-60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results show the following: (1) The rare isotope 3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (2) The Fe/O ratio decreases with increasing energy up to ~10 MeV/nuc in ~92% of the events and up to ~60 MeV/nuc in ~64% of the events. (3) Heavy ion abundances from C-Fe exhibit systematic M/Q-dependent enhancements that are remarkably similar to those seen in 3He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks in energizing particles up to ~60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population with a heavy ion enrichment pattern that is organized according to the ion's mass-per-charge ratio. These new results indicate that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor to the CME shock acceleration process.
Cohen Christina Mae S.
Desai Mihir I.
Dwyer Joesph R.
Gold Robert E.
Krimigis Stamatios M.
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