Date of Award

3-19-2008

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Christopher G. Smithtro, PhD

Abstract

Solar flares release energy, primarily at X-ray and EUV wavelengths, which is then absorbed mainly in Earth's ionosphere. This non-uniform absorption of energy alters the ionosphere's structure and can change the propagation of electromagnetic waves causing errors in GPS navigation, false radar echoes, and loss of High Frequency (HF) radio communications. Accurately modeling the ionospheric response to flares is the first step in predicting, and then mitigating, their effects. Accurately modeling these effects requires solar irradiance at a high cadence, to capture the flare, which may only last minutes, as well as treatment of the effects of photoelectrons. Sami2 is Another Model of the Ionosphere (SAMI2) is a two-dimensional ionospheric model. In its standard form, it is unsuitable for studying solar flare effects because it relies on a daily proxy to specify the solar irradiance. The model was successfully modified to include: secondary ionization of photoelectrons as well as high-cadence solar irradiance from the Flare Irradiance Spectral Model (FISM), and a new photoelectron heating parameterization. The modified SAMI2 was successfully used to model the ionospheric response to the X17 solar flare of 28 October, 2003. Long-lived enhancements in the total electron content (TEC) were observed as was an asymmetric increase in electron temperature due to increased photoelectron heating. Increases in electron temperature of more than 500 K were observed in the mid-latitudes of the Northern Hemisphere without a corresponding increase in the Southern Hemisphere.

AFIT Designator

AFIT-GAP-ENP-08-M08

DTIC Accession Number

ADA481032

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