Spatial and Temporal Evolution of Different-Scale Ionospheric Irregularities in Central and East Siberia During the 27–28 May 2017 Geomagnetic Storm

We present a multi-instrumental study of ionospheric irregularities of different scales (from tens of centimeters to few kilometers) observed over the Central and East Siberia, Russia, during a moderate-to-strong geomagnetic storm on 27–28 May 2017. From high-frequency (HF) and ultrahigh-frequency (UHF) radar data, we observed an intense auroral backscatter developed right after the initial phase of the geomagnetic storm. Additionally, we examined variations of Global Positioning System (GPS)-based ROT (rate of TEC changes, where TEC is total electron content) for available GPS receivers in the region. Ionosondes, HF, and UHF radar data exhibited a presence of intense multi-scale ionospheric irregularities. We revealed a correlation between different-scale Auroral/Farley-Buneman ionospheric irregularities of the E layer during the geomagnetic storm. The combined analysis showed that an area of intense irregularities is well connected and located slightly equatorward to field-aligned currents (FACs) and auroral oval at different stages of the geomagnetic storm. An increase and equatorward displacement of Region 1 (R1)/Region 2 (R2) FACs leads to appearance and equatorward expansion of ionospheric irregularities. During downward (upward) R1 FAC and upward (downward) R2 FAC, the eastward and upward (westward and downward) E × B drift of ionospheric irregularities occurred. Simultaneous disappearance of UHF/HF auroral backscatter and GPS ROT decrease occurred during a prolonged near noon reversal of R1 and R2 FAC directions that accompanied by R1/R2 FAC degradation and disappearance of high-energy auroral precipitation.