Long-Lasting Poloidal ULF Waves Observed by Multiple Satellites and High-Latitude SuperDARN Radars

Abstract

Poloidal ultralow frequency (ULF) waves between 5 and 10 mHz were observed by multiple satellites and three high-latitude Super Dual Auroral Radar Network radars during the recovery phase of a moderate geomagnetic storm on 24–27 January 2016. The long-lasting ULF waves were observed in the magnetic field and energetic particle flux perturbations during three successive passes by two Geostationary Operational Environmental Satellites through the dayside magnetosphere, during which plasmasphere expansion and refilling were observed by two Time History of Events and Macroscale Interactions during Substorms probes. The radial magnetic field oscillation was in phase (∼180° out of phase) with the northward (southward) moving proton flux oscillation at 95 keV, consistent with high-energy drift-bounce resonance signatures of protons with second harmonic poloidal standing Alfvén waves. The longitudinal extent of the waves approached 10 hr in local time on the dayside and gradually decreased with time. High-time-resolution (∼6 s) data from three high-latitude Super Dual Auroral Radar Network radars show that the wave intensification region was localized in latitude with a radial extent of ∼135–225 km in the subauroral ionosphere. No signature of these waves were observed by ground-based magnetometers colocated with the Geostationary Operational Environmental Satellites suggesting that the poloidal waves were high-m mode and thus screened by the ionosphere. During this interval one of the Time History of Events and Macroscale Interactions during Substorms probes observed a bump-on-tail ion distribution at 1–3 keV, which we suggest is the source of the long-lasting second harmonic poloidal ULF waves.