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Sources of Variability in the Topside Ionosphere SOURCES OF VARIABILITY IN THE TOPSIDE IONOSPHERE by Jessica M. Hawkins APPROVED BY SUPERVISORY COMMITTEE: ___________________________________________ Phillip C. Anderson, Chair ___________________________________________ Roderick A. Heelis ___________________________________________ Fabiano Rodrigues ___________________________________________ Russell Stoneback ___________________________________________ Lindsay J. King Copyright 2018 Jessica M. Hawkins All Rights Reserved To Charissa and Sandra for study dates; to Evan for keeping me curious with your love of learning; to Simone, Tim, Cory, Shawn, and Blake for encouragement and enduring friendship; and most of all to my parents and brother, for being my first teachers and my bedrock of love all these years SOURCES OF VARIABILITY IN THE TOPSIDE IONOSPHERE by JESSICA M. HAWKINS, BS, MS DISSERTATION Presented to the Faculty of The University of Texas at Dallas in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY IN PHYSICS THE UNIVERSITY OF TEXAS AT DALLAS May 2018 ACKNOWLEDGMENTS I would like to thank my advisor Dr. Phillip Anderson for showing faith in me, devoting so much time to my education and patiently guiding me through this rite of passage, and to my committee for their time, advice and support. I am grateful to the physics department for sending me to several conferences, including a trip to visit the Jicamarca Radio Observatory which Dr. Fabiano Rodrigues facilitated. Several professors and researchers took the time to mentor and answer my questions at these conferences, including Dr. Maura Hagan, Dr. Roger Varney, Dr. Anja Stromme, and the people at NCAR who host the Advanced Study Program. I would also like to thank my fellow graduate students, several of whom attended practice sessions for my proposal and other presentations. Brian Nathan always encouraged us grad students to help each other and get to know each other. Jessica Smith was a solid friend when exploring the conferences we attended. I had good conversations with Russell Landry and Brian about data processing algorithms over the years, and with Rob McIntosh about how to write the proposal. Weikang Lin patiently went over many practice problems with me before the quantum mechanics qualifier; his tutoring was a strong factor in helping me pass that subject. Dr. Gregory Earle gave me my first instruction in space science as an undergraduate in his CubeSat design class, which he put a lot of work and heart into. Thank you to my teachers at ACE Camp who gave me my first instruction in programming through UTD when I was eleven years old, because that summer was the first time I felt like computer programming was "my v thing." Thank you to the CEDAR program and NSF for funding this research, and to Wiley for permission to reprint material published in the Journal of Geophysical Research. April 2018 vi SOURCES OF VARIABILITY IN THE TOPSIDE IONOSPHERE Jessica M. Hawkins, PhD The University of Texas at Dallas, 2018 ABSTRACT Supervising Professor: Phillip C. Anderson The topside ionosphere is a dynamic region of the Earth’s upper atmosphere that couples with solar and terrestrial regions and affects communication and navigation systems. The solar extreme ultraviolet (EUV) irradiance is a major driver of variability in the topside, and further work is needed to understand how EUV drives variability, particularly in light of the recent availability of spectrally-separated EUV measurements. Variability in the topside is also driven from below, as there is increasing evidence that atmospheric effects are propagated across a broad range of altitudes. The WN4 pattern has been recognized as a signature of non-migrating tides originating in the troposphere, but its variations in the topside have yet to be comprehensively studied. Ionospheric models have struggled to accurately represent the shape and variability of topside ion density profiles, in part due to the relative scarcity of in situ measurements. Nevertheless, empirical models such as the internationally-recognized standard International Reference Ionosphere (IRI) provide a crucial resource to scientists, and improvements to IRI are ongoing. vii This dissertation addresses these research needs in three studies. First, we investigated the response of the topside ionosphere to EUV variability using thermal plasma measurements from the Defense Meteorological Satellite Program (DMSP) over 23 years, a period of time never considered before. The response was found to be closely related to the composition due to the effect of this parameter on the scale height. The composition varies dramatically with the solar cycle and the SZA, and these changes in composition have a compounding effect on the response of the topside ionosphere to changes in solar EUV irradiance. We investigated and quantified the signature of WN4 in the topside ionosphere across local time, season, and varying levels of solar activity using monthly averages of ion densities from DMSP. This study provides compelling evidence of the effects of tropospheric weather on space weather even at DMSP altitudes, which had not been comprehensively presented before. Tidal patterns are strongly present along the magnetic equator throughout the year, and WN4 is clearest at September equinox. During solstice months the WN4 signature is modified by zonal and meridional winds. WN4 moved eastward with increasing F10.7 and drifted eastward at about 2o GLON per hour MLT. To address the scarcity of in situ topside measurements needed to improve IRI, we presented a new data set of over 11,000 magnetic conjunctions between DMSP and C/NOFS in 2009-2015. We investigated the error of the most recent version of IRI in reproducing the topside profile shape under different conditions. The model was found to underestimate the plasma scale height in the morning but matched the profile shape well in the afternoon. The percent error showed viii patterns consistent with a diffusive equilibrium condition in the afternoon, whereas strong ion flows in the morning produced a more complex relationship between the Ni profile shape and the plasma temperatures. ix TABLE OF CONTENTS ACKNOWLEDGMENTS …………………………………………………………………… v ABSTRACT …………………………………………………………………………………. vii LIST OF FIGURES …………………………………………………………………………. xii LIST OF TABLES ………………………………………………………………………….. xvi CHAPTER 1 INTRODUCTION …………………………………………………………... 1 1.1 The Topside Ionosphere ……………………………………………………………. 1 1.2 Geomagnetic Field Geometry, Winds and Effects on the Topside ………………… 5 1.3 Solar EUV Origin, Variability, and Effects on Topside Ionosphere ………………. 7 1.3.1 Origin and variability ………………………………………………………….. 7 1.3.2 Measurements and models …………………………………………………….. 7 1.3.3 Ionospheric effects …………………………………………………………….. 9 1.4 Atmospheric Tides and Coupling with Ionosphere-Thermosphere ………………... 11 1.4.1 WN4 and DE3 …………………………………………………………………. 11 1.4.2 DE3 propagation, WN4 in the F-region, and impact of WN4 on the upper atmosphere ……………………………………………………………………………. 13 1.4.3 Previous measurements and results in the topside ionosphere ………………… 15 1.5 Modeling of Electron Density Profiles …………………………………………….. 16 1.5.1 Scale height and transition height in the topside and modeling of topside electron density profiles ……………………………………………………………………….. 16 1.5.2 Methods of topside ion density profile reconstruction and estimation of the topside scale height …………………………………………………………………………… 17 CHAPTER 2 SCIENTIFIC OBJECTIVES AND RELEVANCE ………………………… 20 2.1 Research Overview ………………………………………………………………… 20 x 2.2 Relevance to Research Community ………………………………………………... 22 CHAPTER 3 DATA SOURCES AND MODELS ………………………………………... 25 3.1 TIMED SEE ……………………………………………………………………….. 25 3.2 SDO EVE ………………………………………………………………………….. 25 3.3 DMSP ……………………………………………………………………………… 25 3.4 C/NOFS ………………………………………………………………………….... 27 3.5 IRI …………………………………………………………………………………. 27 CHAPTER 4 TOPSIDE IONOSPHERIC RESPONSE TO SOLAR EUV VARIABILITY 29 4.1 Data ………………………………………………………………………………… 29 4.2 EOF Analysis ……………………………………………………………………… 39 4.3 Discussion …………………………………………………………………………. 45 4.4 Conclusions ………………………………………………………………………… 47 CHAPTER 5 WN4 VARIABILITY IN DMSP ION DENSITIES ACROSS SEASON, SOLAR CYCLE, AND LOCAL TIME ……………………………………………………………... 50 5.1 Satellites and Instrumentations ……………………………………………………. 50 5.2 Analysis Methods …………………………………………………………………. 51 5.3 Seasonal Variations ……………………………………………………………….. 53 5.4 Solar Cycle Variations ……………………………………………………….......... 60 5.5 Local Time Variations …………………………………………………………….. 65 5.6 Conclusions ……………………………………………………………………...... 69 CHAPTER 6 TOPSIDE PROFILE SHAPE VARIATIONS USING DMSP / C/NOFS CONJUNCTIONS AND IRI ……………………………………………………………….. 72 6.1 Satellite Conjunctions Data Set ……………………………………………………. 73 6.2 Analysis Methods …………………………………………………………………... 77 xi 6.3 Results ……………………………………………………………………………… 79 6.4 Conclusions ………………………………………………………………………… 88 CHAPTER 7 CONCLUSION ……..…………………………………………………......... 89 REFERENCES ……………………………………………………………………………... 93 BIOGRAPHICAL SKETCH ……………………………………………………………….. 103 CURRICULUM VITAE xii LIST OF FIGURES 1.1 Typical profiles of the neutral atmospheric temperature (left) and ionospheric plasma density (right.) [The Earth's Ionosphere, 1989] …………………………………………………………2 1.2 Dip latitude as a function of geographic latitude and longitude. [West and Heelis, 1996] ……….5 1.3 Weighted photoionization and photoabsorption cross sections for O+ for Torr and Torr [1979] bands and lines. …………………………………………………………………………………10 4.1 Examples of the
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