Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics and Applied Physics

Department

Physics

First Advisor

Ramon Lopez

Abstract

Some fraction of the solar wind energy is transferred to the Earth magnetosphere and ionosphere. Sometimes this transfer of energy is exceptionally large, producing a magnetic storm. Storms occur when the Interplanetary Magnetic Field (IMF) turns southward and remains southward for an extended period of time. During the main phase of many magnetic storms, the solar wind Mach number is low, and IMF magnitude is large. Under these conditions, the ionospheric potential saturates, and it becomes relatively insensitive to further increases in the IMF magnitude. On the other hand, the dayside merging rate and the potential become sensitive to the solar wind density. This should result in a correlation between the intensity of the auroral electrojets and the solar wind density. In this study, I find several storm events to examine the effect of the solar wind density on the intensity of the auroral electrojets (as measured by the SME index) under the condition of low Mach number and steady IMF. As expected, there is a positive correlation between solar wind density and the SME index. I show that this correlation coefficient gets larger for smaller Mach number when one would expect the effect of density to be more significant. Furthermore, I study the role of solar wind density during an event with the small northward IMF. In the case of northward IMF, since the reconnection regions are limited, the changes of the ionospheric potential caused by the viscous interaction can be greater/comparable to the reconnection-driven potential. I show that the solar wind density and the SME index correlate with small northward IMF during the event. Thus, the solar wind density correlations with the auroral electrojets have the same behavior under two conditions: 1) in the saturation regime and 2) in the event with northward IMF, although very different physics drove them. Moreover, I provide a sample of 314 moderate to strong storms and investigate the correlation between the Dst index and the energy dissipated in the ionosphere. I show that, on average, for the lower Mach number, this correlation decreases. I also show that the ionospheric indices of the storms with the lower Mach number are less correlated to the geoeffectiveness of the solar wind during these storms. As a next step to studying the energy dissipation during the magnetic storms, I study the energy dissipated in the ionosphere through frictional heating, generally referred to as Joule heating. There are several empirical models to estimate Joule heating based on ionospheric currents using the AE index. In this study, I select 12 magnetic storms from the CCMC database and compare the integrated joule heating with the results of empirical models. I also use the SWMF global magnetohydrodynamic simulations for 13 storms to reproduce the correlation between the simulated AE index and simulated Joule heating to examine the empirical models. I find that the scale factor in the empirical model is half the predicted using the SWMF simulations. Finally, at the end of the dissertation, I point out the possible future studies.

Keywords

Geomagnetic storms, Solar wind density, Saturation, Joule heating, SWMF simulation, Mach number

Disciplines

Physical Sciences and Mathematics | Physics

Comments

Degree granted by The University of Texas at Arlington

Included in

Physics Commons

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