Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh12c..02d&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SH12C-02
Physics
2114 Energetic Particles, Heliospheric (7514), 2139 Interplanetary Shocks, 7513 Coronal Mass Ejections, 7807 Charged Particle Motion And Acceleration
Scientific paper
It is presently believed that the energetic (>50 keV/nucleon) ion population accelerated at interplanetary (IP) shocks driven by fast coronal mass ejections or CMEs originates predominantly from the bulk solar wind. The sophisticated set of high sensitivity mass spectrometers on board the Advanced Composition Explorer (ACE) spacecraft has provided us with detailed composition measurements that have enabled us to address the question of the origin of the source population for such IP shocks. We have surveyed the 0.05-10.0 MeV/nucleon elemental abundances of 48 IP shocks observed by the Ultra Low Energy Isotope Spectrometer (ULEIS) on board ACE from October 1997 through November 2000. Our survey shows that 3He ions are accelerated at 25 IP shocks with the 3He/4He ratio being enhanced between factors of ~3-600 over the solar wind value. Our results also show that the mean abundances of heavier elements such as C, N, O, Ne, Mg, Si, S, Ca, and Fe are markedly different when compared with the corresponding abundances measured in the solar wind. We also find that the elemental composition of IP shocks is remarkably similar to that of the energetic ions present in the interplanetary medium upstream of the shocks. We conclude that the 3He and heavy ion enhancements at IP shocks cannot be attributed to shock acceleration of thermal solar wind ions. We suggest that IP shocks accelerate a suprathermal or energetic seed population comprising ions left over from impulsive solar flares as suggested by Mason et al. (1999), as well as those left over from large gradual solar energetic particle events or SEPs.
Desai Mihir I.
Dwyer Joesph R.
Mason Glenn M.
Mazur J. E.
Skoug Ruth M.
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