New Insights into Solar Energetic Particle Events from ACE and Wind

Allan J. Tylka

Abstract

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
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        e-mail: tylka@gamma.nrl.navy.mil
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