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New Insights into Solar Energetic Particle Events from ACE and Wind
Allan J. Tylka
Solar energetic particle (SEP) events are occasional bursts of high-energy
particles from the Sun. The largest SEP events increase the radiation
intensity in near-Earth space by 4-5 orders of magnitude for periods ranging
from hours to several days. Because of their episodic, highly-variable,
and (presently) unpredictable nature, these events are one of the primary
constraints on the technological utilization of space and in the design
and operation of space systems.
New instruments on Wind and ACE, with geometry factors which are ~100x
larger than those in previous solar cycles, have enabled us to make unprecedented,
detailed studies of temporal evolution in composition and spectra over
a wide range of energies and species. We also have new information
on ionization states and isotopic composition, as well as simultaneous
observations of the very fast CMEs that drive the coronal and interplanetary
shocks which are the cause of the largest SEP events. I will show how these
new observations have sharpened our insights and pointed us toward critical
elements of the underlying physics of SEP production which have not been
adequately considered in the past. Of particular importance are new models
of interplanetary transport, which take into account the key roles of CME-driven
shocks and of particle-amplified Alfvn waves in very large SEP events.
I will also review some of this recent modeling work and comment on new
questions and challenges.
Organization: US Naval Research Laboratory
Address: Code 7654
Naval Research Laboratory
4555 Overlook Ave, SW
Washington, DC 20375-5352
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