Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh11d..11m&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SH11D-11
Physics
2114 Energetic Particles, Heliospheric (7514), 2118 Energetic Particles, Solar, 2139 Interplanetary Shocks, 2152 Pickup Ions, 7513 Coronal Mass Ejections
Scientific paper
Energetic particle acceleration is one of the key features of fast CME events. It has long been known that in CME-related solar particle events, the peak intensities of particles below 10 MeV/nuc often occur at the shock passage, and not in the initial acceleration process much closer to the sun. This acceleration of energetic particles by interplanetary shocks has been extensively studied and modeled, and yet the seed population for the acceleration mechanism remains to be identified. Because the ion composition of the accelerated particles is roughly similar to solar system abundances, it has been presumed that the solar wind is the source. Yet discrepancies in both composition and spectral form between models and observations show that a complete picture has yet to be synthesized. Recent observations on Ulysses and Wind have shed new light on these questions: first, it has been found that the solar wind continuously exhibits a suprathermal tail; second, singly ionized He -- extremely rare in the solar wind -- is enhanced by a factor of ~1000 in corotating shocks. More recently, ACE observations have shown that a sizable fraction of interplanetary shock events and CME-related solar particle events show large enhancements of the rare isotope 3He. These tracer ions, He+ and 3He, are evidence that the energetic particle population is not accelerated out of the bulk thermal pool, but rather out of the suprathermal energy region above the solar wind bulk speed. The suprathermal region has numerous ion sources (e.g., solar wind suprathermal tail, pick-up ions, and remnant suprathermals from prior solar and/or interplanetary activity), and varies in intensity more than the solar wind itself. Understanding the properties of this population, including temporal and spatial variations, and the details of the injection mechanism, appears to be a critical challenge for actually predicting or modeling the energetic particle population accelerated by a given shock.
Desai Mihir I.
Mason Glenn M.
Mazur J. E.
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