Abstract
Medium-scale Traveling Ionospheric Disturbances (MSTIDs) are prominent
and ubiquitous features of the mid-latitude ionosphere, and are observed
in Super Dual Auroral Radar Network (SuperDARN) and high-resolution
Global Navigational Satellite Service (GNSS) Total Electron Content
(TEC) data. The mechanisms driving these MSTIDs are an open area of
research, especially during geomagnetic storms. Previous studies have
demonstrated that night-side MSTIDs are associated with an
electrodynamic instability mechanism like Perkins, especially during
geomagnetically quiet conditions. However, day-side MSTIDs are often
associated with atmospheric gravity waves. Very few studies have
analyzed the mechanisms driving MSTIDs during strong geomagnetic storms
at mid-latitudes. In this study, we present mid-latitude MSTIDs observed
in de-trended GNSS TEC data and SuperDARN radars over the North American
sector, during a geomagnetic storm (peak Kp reaching 9) on September
7-8, 2017. In SuperDARN, MSTIDs were observed in ionospheric backscatter
with Line Of Sight (LOS) velocities exceeding 800 m/s. Additionally,
radar LOS velocities oscillated with amplitudes reaching +/-$500 m/s as
the MSTIDs passed through the fields-of-view. In detrended TEC, these
MSTIDs produced perturbations reaching ~50 percent of
background TEC magnitude. The MSTIDs were observed to propagate in the
westward/south-westward direction with a time period of
~15 minutes. Projecting de-trended GNSS TEC data along
SuperDARN beams showed that enhancements in TEC were correlated with
enhancements in SuperDARN SNR and positive LOS velocities. Finally,
SuperDARN LOS velocities systematically switched polarities between the
crests and the troughs of the MSTIDs, indicating the presence of
polarization electric fields and an electrodynamic instability process
during these MSTIDs.