Subauroral Flow Channel Structures and Auroral Undulations Triggered by Kelvin‐Helmholtz Waves

Abstract

AbstractWe investigate Kelvin‐Helmholtz (K‐H) waves on/near the magnetopause and surface waves near the plasmapause—in the outer region of the plasmasphere: in the hot zone—by utilizing multi‐instrument/satellite observations. Our main aim is to study how the K‐H waves and the K‐H instability mechanisms impacted the subauroral and auroral regions during the geomagnetic storms of May 27–29 and July 16, 2017. For the subauroral region, we specify the structured flows as Sub‐Auroral Polarization Streams Wave Structures (SAPS‐WS) and the combined flows—created by Abnormal Sub‐Auroral Ion Drifts (ASAID) and SAID or SAPS—as a complex equatorward‐poleward ASAID‐SAID or SAPS‐ASAID. For the auroral zone, we identify the large auroral undulations appearing inside the auroral zone. The correlated observations of the K‐H waves, the structured or complex subauroral flows and large auroral undulations, and the local geomagnetic field oscillations confirm the connections of both the subauroral flows and the auroral undulations with the K‐H waves via the eigenfrequency of the Near‐Earth Plasma Sheet (NEPS) resonator activated by the K‐H waves. For the first time, we demonstrate the simultaneous detections of K‐H waves near the magnetopause and surface waves near the plasmapause in the hot zone on July 16, 2017, and conclude their coupling via the NEPS resonator's eigenfrequency. Thus, the surface waves near the plasmapause were the manifestation of the undulating (or rippled) earthward inner boundary of the NEPS that led to the development of ASAID‐SAID/SAPS‐ASAID or SAPS‐WS in the subauroral region and to the large auroral undulation inside the auroral zone.