ENERGETIC PARTICLE ACCELERATION AND PROPAGATION

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ENERGETIC PARTICLE ACCELERATION AND
PROPAGATION T.T. VON ROSENVINGE et al.
WEST
EAST
Fe/O (normalized)
FLARE LONGITUDE
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We have studied event-averaged Fe abundances at
energies above 2 MeV/nuc in a large sample of
solar energetic particle events. Fe/O ratios in
these events, here normalized to Fe/O in the
solar corona, are roughly organized by the solar
longitude of the associated flare relative to the
observer. Western events are generally Fe-rich
suggesting they are dominated by particles
accelerated in flare processes close to the Sun.
Eastern events are dominated by interplanetary
shock accelerated particles and are nearly always
Fe-poor. Additional factors that affect
abundances include the structure of the
interplanetary magnetic field, which influences
magnetic connection, and the presence of passing
interplanetary shocks not related to the solar
event of interest. Events in red are the most
energetic with measurable Fe gt25 MeV/nuc. The
blue events are the least energetic. The green
events have high intensities of oxygen near 2
MeV/nuc but not above 25 MeV/nuc. These have
intermediate strength shocks that do not produce
high energy ions. Most are from the eastern
hemisphere. We conclude that flares are an
important component of the complicated process
leading to radiation hazards near Earth.