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Effects of the Radiation Belt on the Plasmasphere Distribution Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 12-2020 Effects of the Radiation Belt on the Plasmasphere Distribution Stefan Thonnard Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Plasma and Beam Physics Commons Recommended Citation Thonnard, Stefan, "Effects of the Radiation Belt on the Plasmasphere Distribution" (2020). All Graduate Theses and Dissertations. 8007. https://digitalcommons.usu.edu/etd/8007 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. EFFECTS OF THE RADIATION BELT ON THE PLASMASPHERE DISTRIBUTION by Stefan Thonnard A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Physics Approved: ______________________ ______________________ Robert Schunk, Ph.D. Eric Held, Ph.D. Major Professor Committee Member ______________________ ______________________ Bela Fejer, Ph.D. Charles Swenson, Ph.D. Committee Member Committee Member ______________________ ______________________ Mike Taylor, Ph.D. D. Richard Cutler, Ph.D. Committee Member Interim Vice Provost of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2020 ii Copyright © Stefan Thonnard 2020 All Rights Reserved iii ABSTRACT Effects of the Radiation Belt on the Plasmasphere Distribution by Stefan Thonnard, Doctor of Philosophy Utah State University, 2020 Major Professor: Dr. Robert Schunk Department: Physics This study examines the distribution of plasmasphere ions in the presence of warmer radiation belt particles. Recent satellite observations of the radiation belts indicate the existence of a population of warm ions with energy 100 keV to 1 MeV trapped along magnetic field lines. Although likely having terrestrial origin, these lower energy trapped particles consisting of H+, He+ and O+ ions do not have the same morphology as the colder ions created in the ionosphere and transported along field lines into the plasmasphere. To explore the interaction of these two coexisting populations, this study initially developed a simple one-dimension model of the F-region ionosphere and examined the effects of inserting an independent species of charge particles. The effort was extended by creating a representative density distribution of radiation particles using the Air Force AE9AP9 radiation belt model and incorporating them as an independent species into the two-dimensional solution for the transport of convecting plasma along a magnetic field line in the Ionosphere-Plasmasphere Model (IPM). The two models were used to explore different solar and geomagnetic conditions, and determined that the outer radiation belt has the greatest effect on the background plasmasphere in the equatorial iv region at 18,500 km altitude. During solar maximum conditions the radiation belt particle density is negligible compared to the background plasmasphere. However, this investigation shows that during solar minimum the outer radiation belt could impart up to a 10% change in the plasmasphere distribution, predominately H+. Furthermore, the warm O+ ions from the radiation belt account for most of the effect on the colder plasmasphere H+ distribution. Additionally, the study suggests that during moderate but relatively frequent solar storms when the outer plasmasphere is depleted, the rapid population of O+ into the outer radiation belt may increase the time to refill the cold plasma in that region by 30%. (162 pages) v PUBLIC ABSTRACT Effects of the Radiation Belt on the Plasmasphere Distribution Stefan Thonnard This study examines the interaction of plasma, ions and electrons created by Solar illumination in the Earth’s upper atmosphere, that travels along magnetic field lines filling the Plasmasphere, and the naturally occurring trapped particles known as the outer radiation belt. Although these two science disciplines have been largely worked independent of each other due the vast differences in the energy of the particles, recent satellite observations indicate a large population of particles with lower energy and greater mass also exist in the outer radiation belt. This study shows that during conditions of low solar output in an 11-year cycle, these newly identified particles may have an effect on the background plasma flowing up from the upper atmosphere along the magnetic field lines. Additionally, the study indicates that relatively frequent small solar storms that rapidly increase the radiation belt density may repel the upward flow of plasma, increasing the time for the background to return to the pre-storm conditions by 30%. vi ACKNOWLEDGMENTS Words cannot express my gratitude for the encouragement and support I received from my family and friends at home and at Utah State University throughout my journey. I would like to thank my major professor, Dr. Schunk, for his dedication to my success. Our many email exchanges and evening on the phone guided me through the research and to the completion of my dissertation. I would also like to thank the Air Force Research Laboratory and staff who provided the AE9AP9 radiation model and the continued support by Paul O’Brien to help me adapt it for my research. I extend a special thank you to my committee members, Karalee and the faculty and staff who assisted me at every turn. I am eternally indebted to my wife Lynn and two sons Anthony and Max, who dropped everything to follow me to Logan as well as my daughter Rachael who I missed as she stayed behind to finish her senior year. I was too often absent from family activities, but their steadfast patience and encouragement kept me going every step of the way. I couldn’t have done this without them. Finally, I am forever thankful for my parents love, understanding and support; I miss them very much. Stefan Thonnard vii CONTENTS Page ABSTRACT ...................................................................................................................... iii PUBLIC ABSTRACT ....................................................................................................... v ACKNOWLEDGMENTS ................................................................................................. vi LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES ........................................................................................................... x Chapter I Introduction ........................................................................................................ 1 Sun and Solar Wind ................................................................................................ 1 Magnetosphere and Radiation Belts ....................................................................... 3 Ionosphere and Plasmasphere ................................................................................ 6 Motivation for Proposed Research.......................................................................... 8 Chapter II Ionosphere-Plasmasphere and Radiation Belt Models ................................... 10 Ionosphere-Plasmasphere Model (IPM) .............................................................. 10 Sample Plasma Density from IPM Simulations.................................................... 12 Radiation Belt Model ........................................................................................... 24 Sample Radiation Flux from AE9AP9 Simulations ............................................ 29 Chapter III Coupled Model Approach ............................................................................. 34 Coupling IPM and AE9AP9 ................................................................................. 34 Selecting Parameters for the 4 Study Cases ......................................................... 36 Technique for Representing Flux as a Density .................................................... 38 Density Derived from AE9AP9 Simulations ........................................................ 42 Chapter IV Results ........................................................................................................... 47 The Bounding Conditions for Plasmasphere and Radiation Belt Interaction ...... 47 Simulation of Plasmaspheric Response to the Radiation Belt Particles .............. 51 Storm Depleted Plasmasphere and Recovery ....................................................... 54 Chapter V Conclusion ...................................................................................................... 59 References ........................................................................................................................ 63 viii Appendices ....................................................................................................................... 67 Appendix A Radiation Belt Impact on Space Systems ........................................ 68 Motivation for Model Improvement ........................................................ 68 Anthropogenic Radiation Belt Variations ................................................ 70 Renewed Threat ....................................................................................... 74 Appendix B Charged Particles in a Magnetic Field ............................................
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