Multi-Instrument Observations of Physical Processes in the Arctic Ionosphere and Derived Applications

Abstract

The ionosphere is the source of the largest errors in satellite-based navigation and positioning, transionospheric radio communications, and certain satellite-based radar remote sensing techniques. A proper understanding of ionospheric dynamics and its coupling with space weather can help mitigate these errors. Specifically, ionospheric electron density and scintillation forecasting would significantly improve reliability of navigation and positioning systems. This Ph.D. thesis is primarily concerned with the physical processes in the terrestrial Arctic upper atmosphere. Additionally to this, two studies about lower-latitude regimes and a global ionosphere mapping study are also presented. Whenever multi-instrument observations were available, these measurements were combined to obtain a more complete physical description of the underlying processes. All of the studies presented employ the observation-based approach with utilization of GNSS-derived measurements as the primary data source, and the primary subject of the research being the terrestrial atmosphere (the ionized part, the neutral part, or both). The collected measurements are used to construct a model of the underlying physical processes. The complexity of the studied atmospheric processes often required multiple, independent measurements of various physical parameters. These results are then combined such that they complement each other and provide validation. Some of the important findings of this work include (1) the analysis of an interplanetary coronal mass ejection (ICME) induced negative storm phase at high latitudes in February 2014 exhibited thermospheric O/N2 decrease due to atmospheric heating, increased ion flow in the topside ionosphere, and an increase in polar patch formation inhibition, all of which lasts for several days. These appear to be general features of these types of geomagnetic storms. (2) During an energetic, mixed high-speed stream (HSS) and ICME-induced storm in March 2015, GPS phase scintillation II was found to be mapped to the poleward side of the westward electrojet and to the edge of the eastward electrojet region. At the same time, the scintillation was largely collocated with fluxes of energetic electron precipitation observed by DMSP satellites, with the exception of a period of pulsating aurora when only very weak currents were observed. (3) Based on measurements employing a space-qualified GPS receiver placed on a mountain at the Haleakala observatory on the Hawaiian island of Maui, it was found that simulated surface-reflection signals and the measured reflection signals were revealing matching spectral structures of the reflected signals that could lead to extraction of parameters of sea surface roughness, surface wind speed, and direction. (4) 4-year long regional electron density observations from Thule, Greenland revealed a series of findings: strong correlation with solar extreme ultraviolet (EUV) spectral irradiance that is related to solar rotation and sunspot numbers, increased electron density variability during equinoxes that is related to the Russell-McPherron effect, and a strong influence of ambipolar diffusion as a function of ionospheric E layer conductivity. (5) The polar cap index rate of change showed significant differences during ICME and HSS-induced storms. This indicates that the energy input into the polar cap occurs at significantly different rates for these two phenomena which results in some differences in the induced geomagnetic storm evolution.