Elemental Abundances Observed by ACE During Ground Level Events

Details Elemental Abundances Observed by ACE During Ground Level Events Elemental Abundances Observed by ACE During Ground Level Events

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsh43b..03v&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH43B-03

Astronomy and Astrophysics

Astrophysics

7500 Solar Physics, Astrophysics, And Astronomy, 7514 Energetic Particles (2114), 7519 Flares

Scientific paper

We report on elemental abundances of solar energetic particles (SEPs) observed between 14 and 60 MeV/nucleon by the Solar Isotope Spectrometer on the Advanced Composition Explorer (ACE) spacecraft. In particular, we focus on SEP events which were also observed by neutron monitors on the ground. There were 14 such Ground Level Events (GLEs) between the launch of ACE in August, 1997 and the present. Three of the first five SEP events observed by ACE were GLEs. These three events had approximately 'impulsive' composition (e.g., Fe/O ~ 8 X coronal) but appeared otherwise to be gradual events. No such events have been seen in the 11 subsequent GLEs. However, 6 of the 11 GLEs have event-averaged Fe/O increasing with increasing kinetic energy. The causes of these enhancements of heavy elements are poorly understood. This is perhaps not surprising since multiple seed particle populations and acceleration processes together with escape from the accelerating regions and propagation to the observer can all play a role. Several possible scenarios will be described and evaluated. This research was supported by NASA at the Goddard Space Flight Center, the California Institute of Technology (under Grant NAG5-12929), and the Jet Propulsion Laboratory.

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