Medium Scale Travelling Ionospheric Disturbances (MSTIDs) are quasi-wavelike structures in ionospheric density that can be sensed using Global Navigational Satellite Service (GNSS) Total Electron Content (TEC) techniques and coherent scatter radars such as the Super Dual Auroral Radar Network (SuperDARN). MSTIDs, especially those observed during quiet times and on the night side, have been known to be driven by electrodynamic instability processes, such as the Perkins instability. In this work, SuperDARN is used in conjunction with GNSS TEC data to investigate MSTIDs during a major geomagnetic storm on September 7-8th, 2017. The interval of this study is in the North American region between 23UT and 3UT, during the peak of the storm, when Kp reached 9. MSTIDs during the interval were investigated by previous studies. However, the roles of electrodynamic instability processes and atmospheric gravity waves (AGWs) in driving the MSTIDs were not determined. GNSS TEC fluctuations associated with the MSTIDs were strong, reaching up to half of background TEC. In SuperDARN, MSTID signatures were observed in power measurements. Meanwhile, SuperDARN line-of-sight (LOS) plasma velocity corresponding to MSTID structures exceeded $pm$500 m/s. This systemic change in the polarity of SuperDARN LOS velocities is indicative of strong polarization electric fields and therefore driving electrodynamic instability processes. This work therefore presents signatures of storm time electrified MSTIDs in mid-latitude North America. / Master of Science / The upper atmosphere contains a region called the ionosphere, where ionized gas called plasma exists. This plasma can be sensed using satellites and ground-based receivers. Specifically, Global Navigational Satellite Service constellations, such as GPS, are good candidates for this technique. This method yields a column density measurement of electrons and is known as GNSS TEC. Most of the time, GNSS TEC is used in a low resolution format, but a high-resolution format is available. This high-resolution GNSS TEC allows for smaller structures in the ionosphere to be investigated. Ionospheric plasma can also be sensed using ground based radar systems, such as the Super Dual Auroral Radar Network (SuperDARN). Combining GNSS TEC and SuperDARN allows for investigation of disturbed structures in the Ionosphere. These structures include wave-like behavior, with time scales under 30 minutes, called Medium Scale Travelling Ionospheric Disturbances (MSTIDs). When these MSTIDs are investigated during times where the Sun is especially active, some unexpected results are found. Most importantly, SuperDARN radars see plasma velocity behave as if it is affected by MSTID structures. This suggests that the buoyancy force which drives the MSTIDs is an electric force instead of a pressure gradient. This behavior has been shown before, but only at night times, specifically when the Sun is not as active. Therefore, this work presents a new kind of MSTIDs.

The ionosphere is an electrically charged atmospheric region which is coupled to the sun, the magnetosphere, and the neutral atmosphere. The ionospheric state can significantly impact technological systems, especially those which utilize radio frequency energy. By studying ionospheric disturbances, it is possible to gain a deeper understanding of not only the ionosphere itself, but also the natural and technological systems it is coupled to. This dissertation research utilizes high frequency (HF) radio remote sensing techniques to study three distinct types of ionospheric disturbances. First, ground magnetometers and a new mid latitude SuperDARN HF radar at Blackstone, Virginia are used to observe magnetospheric Pi2 ultra low frequency (ULF) pulsations in the vicinity of the plasmapause. Prior to these pulsations, two Earthward moving fast plasma flows were detected by spacecraft in the magnetotail. Signatures of inner magnetospheric compression observed by the Blackstone radar provide conclusive evidence that the plasma flow bursts directly generated the ground Pi2 signature via a compressional wave. This mechanism had previously been hypothesized, but never confirmed. Next, ten SuperDARN radars in the North American Sector are used to investigate the sources and characteristics of atmospheric gravity waves (AGW) associated medium scale traveling ionospheric disturbances (MSTIDs) at both midlatitudes and high latitudes. Consistent with prior studies, the climatological MSTID population in both latitudinal regions was found to peak in the fall and winter and have a dominant equatorward propagation direction. Prior studies suggested these MSTIDs were caused by mechanisms associated with auroral and space weather activity; however, it is shown here that the AE and Sym-H indices are poorly correlated with MSTID observations. A new, multi-week timescale of MSTID activity is reported. This leads to the finding that MSTID occurrence is highly correlated with an index representative of polar vortex activity, possibly controlled by a filtering mechanism that is a function of stratospheric neutral wind direction. Finally, a case study of a radio blackout of transionospheric HF communications caused by an X2.9 class solar flare is presented. This study demonstrates the potential of a novel technique employing signals of opportunity and automated receiving networks voluntarily created by an international community of amateur radio operators. / Ph. D.