Date of Award
Doctor of Philosophy (PhD)
Electrical, Computer & Energy Engineering
Acoustic gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) have a significant impact on the thermosphere-ionosphere, both by increasing ionospheric variability and transporting energy and momentum. This work demonstrates the use of Dynasonde data products (electron density, ionospheric tilts, Doppler speed) for the study of TIDs and AGWs. The features of Dynasonde-capable instruments make them uniquely fit for this purpose, allowing for the complete characterization of TID activity over large time periods. New spectral analysis techniques are developed, allowing for the accurate characterization of the TID spectrum from periods of several minutes (AGWs) to harmonics of 24 hours (atmospheric tides). A new approach for determining the mean Power Spectral Density (PSD) of TIDs is developed based on the Lomb-Scargle and Welch methods and its accuracy is demonstrated using both synthetic data and ionospheric tilt data from Wallops Island, VA. The method is then used to determine the seasonal variations in the ionosphere due to AGWs. PSDs and integral PSDs of the ionospheric tilts and Doppler speed are used to highlight the presence of a well-known winter peak in TID activity at mid-latitudes in the northern hemisphere, and also a new, previously unreported summer peak. The full set of propagation parameters (frequency, horizontal and vertical wavelength, propagation azimuth) is determined using the electron density and tilt data from Wallops Island. Using these results and the Whole Atmosphere Model (WAM), the agreement between the TID parameters and the gravity wave dispersion relation is demonstrated convincingly within the uncertainty for the first time. This further proves that the observed TIDs are caused by underlying AGWs. Using a month-long dataset obtained in October 2013 at Wallops Island, the statistical distributions of the propagation azimuth, vertical and horizontal wavelength and horizontal phase speed are studied, including their variation with altitude. The impact of AGW dissipation on the background thermosphere-ionosphere is investigated using gravity wave polarization relations and a model of the neutral-ion coupling, obtaining estimates of the momentum flux. In addition to the geophysical results obtained here, the general character of the methods used to obtain them will allow for further studies using Dynasonde data.
Negrea, Cătălin, "Characteristics, Variability and Impact of Atmospheric Gravity Waves in the Thermosphere-Ionosphere as Determined from Dynasonde Data" (2016). Electrical Engineering Graduate Theses & Dissertations. 15.