Evidence for a Two-Stage Acceleration Process in Large Solar Energetic Particle Events |
| |
Authors: | M I Desai G M Mason R E Gold S M Krimigis C M S Cohen R A Mewaldt J E Mazur J R Dwyer |
| |
Institution: | (1) Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA;(2) The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA;(3) California Institute of Technology, Pasadena, CA 91125, USA;(4) The Aerospace Corporation, 15049 Conference Center Drive, CH3/210, Chantilly, VA 20151, USA;(5) Florida Institute of Technology, Melbourne, FL 32901, USA |
| |
Abstract: | 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 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. (2) The rare isotope 3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (3) The heavy ion abundances are not
systematically organized by the ion’s M/Q ratio when compared with the solar wind values. (4) 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. |
| |
Keywords: | Sun: energetic particles Sun: coronal mass ejections Sun: flares |
本文献已被 SpringerLink 等数据库收录! |
|