Medium Scale Travelling Ionospheric Disturbances sensed with GNSS TEC and SuperDARN

Abstract

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.