Sub‐Auroral Flows and Associated Magnetospheric and Ionospheric Phenomena Developed During 7–8 September 2017

This study investigates the Sub‐Auroral Polarization Streams (SAPS) and Sub‐Auroral Ion Drifts (SAID) along with the associated magnetospheric and ionospheric phenomena developed during 7–8 September 2017. Then, a series of substorms occurred before and during the geomagnetic storm (SYM‐Hmin = −146 nT). Results are obtained by utilizing multi‐point observations. These show that during the pre‐storm period, when the ElectroMagnetic Ion‐Cyclotron waves resulted in drop‐out events, a series of sunward (westward) SAID‐in‐SAPS flows developed in the dusk‐midnight sector due to the small‐scale flow bursts reaching the SAPS channel and the westward SAPS flows were streaming antisunward after midnight. During the storm period, dawnside sunward (eastward) SAPS also developed, Kelvin‐Helmholtz (K‐H) vortices rolled along the magnetopause and the hot zone became structured by reflected K‐H waves near the plasmapause leading to auroral undulations (AUs). New findings include the correlation of AUs and K‐H waves in the structured hot zone implying that the Near‐Earth Plasma Sheet acted as a resonator after activation by the K‐H vortices on the magnetopause. Further evidence is provided by the dayside Equatorward Boundary Intensification and Poleward Moving Auroral Forms of which development was supported by the K‐H vortices on the magnetopause by carrying the magnetosheath plasma into the magnetosphere. Adding to previous studies, new results also include the correlated observations of storm‐enhanced density (SED) plume and poleward drifts underlying both the equatorward plasma bubbles and the higher latitude plasma density depletions, and thus verifying their poleward movement within the SED base and SED plume. Key Points Sunward Sub‐Auroral Ion Drifts‐in‐Sub‐Auroral Polarization Streams (SAPS) flows developed at dusk‐midnight and antisunward SAPS flows after midnight Correlated auroral undulations and Kelvin‐Helmholtz waves (structuring the hot zone) suggest Near‐Earth Plasma Sheet resonator activation Ram drifts depict the poleward drifts of plasma bubbles/depletions within the storm‐enhanced density base/plume