Multispacecraft Observation of the Presubstorm Long‐Lasting Poloidal ULF Wave

• Published in: Geophysical research letters 2021-12, Vol.48 (23), p.n/a
• Main Authors: Rubtsov, Aleksandr V., Mikhailova, Olga S., Mager, Pavel N., Klimushkin, Dmitri Yu, Ren, Jie, Zong, Qiu‐Gang
• Format: Article
• Language: English
• Subjects: Alfven wave; drift‐bounce resonance; magnetic storm; magnetosphere; substorm; ULF wave
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096182

We report global dayside observation of Pc4–5 wave at the late recovery phase of a magnetic storm from seven satellites. Oscillations lasted for 15 hr and revealed the wave appearance before the substorm onset. The continuous observation showed that substorm injections did not affect the wave behavior, and all the wave parameters change was caused by magnetospheric plasma recovery after a magnetic storm. The wave was identified as a second harmonic poloidal Alfvén wave propagating westward with a high azimuthal wave number (|m| ∼ 210) and coupled with 100 keV protons through the drift‐bounce resonance. A large radial gradient of phase space density was an energy source for the wave. Plain Language Summary A multispacecraft observation of the ultralow frequency wave at the dayside of the terrestrial magnetosphere showed the absence of substorm's influence on them. At the same time, a magnetospheric plasma recovery took place after a magnetic storm that probably caused smooth wave parameter change. The observed wave was identified as a second harmonic radially polarized Alfvén wave resonating with energetic protons through the drift‐bounce mechanism. A gradient instability became an energy source for the wave due to a large radial gradient of phase space density. Key Points The ultralow frequency wave was detected on the dayside 30 min before the substorm onset and lasted for 15 hr Substorm injections did not affect the wave structure The energy was transferred from 100 keV protons to the poloidal Alfven wave via the gradient instability