Non-migrating tides are understood to be an important coupling mechanism through which lower atmospheric conditions influence the variability of the near-Earth space environment. Tidal variations have been exhaustively characterized in the mesosphere/lower thermosphere and the upper thermosphere, yet it is not quite known to what extent tides appear in the middle thermosphere due to a lack of global-scale systematic observations. This dissertation addresses the middle thermospheric "gap" of tidal observations. Using far ultraviolet (FUV) observations of the Earth, the recent NASA GOLD and ICON missions retrieve thermospheric parameters, the former from geostationary orbit (GEO) and the latter from low Earth orbit. Both missions infer the daytime column O/N2 ratio, while GOLD also retrieves the daytime thermospheric disk temperature. Traditional spectral tidal decomposition cannot be employed on GOLD data due its incomplete longitude/local solar time sampling. The known limitation introduced by ionospheric contamination of emissions at 135.6 nm and the dependence of the GOLD disk temperature on solar zenith angle both serve as additional obstacles. This dissertation proposes a pair of algorithms, based on the local time sum and difference approaches, that retrieves diurnal and semidiurnal tidal parameters for temperature and O/N2 in a single inversion, while constraining the tidal phase differences in temperature and O/N2 using a general circulation model. The first estimates of non-migrating tidal amplitudes and phases in middle thermospheric temperature and O/N2 using a geostationary observational platform are presented. Comparisons to physics-based and empirical models reveal that modeled amplitudes are generally weaker than the amplitudes retrieved from GOLD data, highlighting the need for better representation of tidal dynamics. In addition, this dissertation proposes a universal approach to systematically reduce the ionospheric contamination of O/N2 and thus determine the true thermospheric tidal variations. The approach considers biases between the remote sensing and ionospheric data sets, and due to its universality can be adapted for any retrieval of O/N2 from far ultraviolet emissions. The modified O/N2 shows a wavenumber-3 pattern indicative of the diurnal eastward propagating zonal wavenumber 2 tide (DE2), where it was not present in the original O/N2. This DE2 presence as well as the finding of DE3 and SE2 signatures in wavenumber-4 patterns is consistent with the theory that upward propagating tides influence the longitudinal structure of the thermospheric composition. / Doctor of Philosophy / A remarkable amount of variability in the upper atmosphere is not explained by the state-of-the-art description of the connected Sun-Earth system. Understanding the mechanisms of said variability is instrumental to achieving operational space weather forecasting, a capability that would alleviate the uncertainties faced by space activities such as GPS. Solar atmospheric tides have been studied as a coupling mechanism between terrestrial weather and space weather, and thus believed to be responsible for much of the variability not accounted for. These tides are periodic planetary-scale oscillations of the atmosphere, principally forced by the heating of the atmosphere by solar radiation. A subset of them, called non-migrating tides, do not track the motion of the Sun across the sky. Non-migrating tides in the upper atmosphere are forced in a myriad of ways, including but not limited to large-scale tropical weather systems and the interactions of the migrating tide with other waves. They are known to redistribute the charged particles of the ionosphere, thus influencing radio communications. This dissertation presents novel methods to studying non-migrating tides in a region of the upper atmosphere, the middle thermosphere (around 150 km altitude), where observations of them are sparse. A pair of methods was devised to overcome the limited sampling of temperature and composition from geostationary orbit, where a satellite appears fixed to a ground-based observer. Another method addresses a limitation that has afflicted prior investigations of non-migrating tides in neutral composition based on far ultraviolet observations. These methods use data collected by the NASA GOLD and ICON missions, modern space-based Earth observation missions that make crucial measurements of the middle thermosphere. The successful development of these methods paves the way for better understanding the nature of upper atmospheric variability introduced by tides. Comparison to models indicate that models generally underestimate the tidal amplitudes. Analysis of neutral composition variations is consistent with the theory that upward propagating tides influence the longitudinal structure of thermospheric composition.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115614 |
| Date | 30 June 2023 |
| Creators | Krier, Christopher Scott |
| Contributors | Aerospace and Ocean Engineering, England, Scott L., Baker, Joseph Benjamin, Bailey, Scott M., Paterson, Eric G. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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