Date of Award

Winter 2012

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Eberhard Moebius

Abstract

The ionic charge states of Solar Energetic Particle (SEP) events provide direct information about the source plasma and the acceleration environment. In this thesis, we mainly build on charge state observation of SEP events during late 1997 to 2000 with from Solar Energetic Particle Ionic Charge Analyzer (SEPICA) on board Advanced Composition Explorer (ACE). We concentrate our effort on the high QFe (≥14) found in the SEP events, and discuss the physical principles of how these elevated charge states are produced. We statistically confirmed the energy dependent charge states found in impulsive SEP events and showed impulsive SEPs are consistent with a normal coronal source. The energy dependent charge states is consistent with stripping model of impulsive events, where the charge states are built through stripping of electrons in the dense lower corona. We found a trend between the charge states and enhancement of heavy ions and 3He at lower SEP energies, but the trend is lost at higher energies, as predicted by the stripping model. We further investigated the variation of mean charge state in impulsive SEPs and found that the elevated mean QFe in impulsive events are due to larger energy loss with stronger adiabatic deceleration. We also surveyed 89 SEP events during the time, seeking high source temperature material accelerated to SEP energies. We found that such events are very rare, and local acceleration of high temperature material may occur in a rare configuration where a second shock plows through the high temperature material of a preceding CME. Among the high QFe events, we also observed impulsive events consistent with source temperature >2MK, even as high as ∼4MK based on a comparison with a model. A few events appear to be impulsive material re-accelerated in interplanetary space. We found that the original charge states of their parent events are re-distributed to different extent, thus the high Q Fe in these events, even at the lowest SEP energies, cannot be used as direct evidence of high source temperature.

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