Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysical & Planetary Sciences

First Advisor

Francis G. Eparvier

Second Advisor

Frances Bagenal

Third Advisor

Scott E. Palo

Abstract

X-ray and extreme ultraviolet (EUV, 0-121.6 nm) emission from the solar corona has long been used to provide insight into the dynamics and evolution of solar flares. The EUV Variability Experiment (EVE) onboard NASA's Solar Dynamics Observatory (SDO) measures the solar spectral irradiance in the EUV at a wide range of temperatures (7,000 K to 10 MK), capturing the complete evolution of the transition region and corona during solar flares. The goal of this thesis is to use the new observations obtained by EVE to quantify how the EUV spectral irradiance varies in response to solar flares. Most observation-based research on solar flares is done by studying individual, usually large, solar flares. My work takes a different approach. From 1 May 2010 to 31 August 2011, SDO observed over 750 solar flares. I created the EVE flare catalog to examine all of these events to produce a complete picture of the EUV variability of flares. In the process, I discovered that flares can be placed into one of five EUV flare categories. The EUV irradiance signature of these categories is unique and closely related to the magnetic structure of the flare region. Confined flares are the most ubiquitous type of flare. They are non-eruptive flares and appear as the sudden brightening of a coherent bundle of coronal loops. Localized eruptive flares are small point-like flares associated with EUV surges or jets. Arcade flares are the classic CSHKP-type flare and are identified observationally by an eruption followed by arcade of flare loops in the corona and two bright ribbons of footpoint emission in the chromosphere and transition region. EUV late phase flares are characterized by two spatially and temporally separate but related reconnection events. Finally, flares that do not fit into any of the four other flare categories are called "strange" flares. I also used the Enthaply-Based Thermal Evolution of Loops (EBTEL) code to model the heating rate of the corona during flares. By fitting the input parameters of the model to the EVE data, I determined that the rate of energy release during reconnection strongly influences the EUV irradiance signature. Each of these EUV flare categories has a different heating rate profile, which is related to the underlying magnetic structure of the flare region.

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