Poleward Moving Auroral Arcs and Pc5 Oscillations

• Published in: Journal of geophysical research. Space physics 2022-08, Vol.127 (8), p.n/a
• Main Authors: Sakurai, T., Wright, A. N., Takahashi, K., Elsden, T., Ebihara, Y., Sato, N., Kadokura, A., Tanaka, Y., Hori, T.
• Format: Article
• Language: English
• Subjects: Alfven waves; aurora; Auroral arcs; Auroral electrons; Auroral emissions; Auroral oval; Auroras; Brightening; Electric arcs; Electric fields; Electron acceleration; Electron precipitation; Emissions; Energy; Extremely low frequencies; Field aligned currents; Ground stations; Ground-based observation; Ionosphere; Kinetic energy; Latitude; Luminosity; Magnetic fields; Magnetohydrodynamic waves; Magnetometers; magnetosphere; Magnetospheres; Mathematical models; Numerical models; Oscillations; Oxygen; Oxygen atoms; Pc5 oscillation; Polar environments; Polar regions; Simulation; Solar wind; Solar wind electrons; Spacecraft; ULF waves
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2022JA030362

We present an example of one‐to‐one correspondence between poleward moving auroral arcs (PMAAs) and Pc5 oscillations observed at the Time History of Events and Macroscale Interactions during Substorms (THEMIS) Ground Based Observatory station Gillam. The PMAAs consisted of four successive intensifications (named PMAA1, PMAA2, PMAA3 and PMAA4) with a period of 3∼4 min over the magnetic latitudes from 68° to 70° in the auroral oval and varied coherently with the H‐component of magnetic field Pc5 oscillations. PMAA1 and PMAA2 appeared clearly at the magnetic latitude ∼69°, and the following two PMAAs, which were dimmer, appeared at the magnetic latitude ∼68°. PMAA1 and PMAA2 exhibited features of field‐line resonances with the maximum luminosity at the magnetic latitude ∼69.5° and ∼69.4°, respectively. The ground Pc5 oscillations were concurrent with toroidal mode Pc5 oscillation observed at the THEMIS‐D, ‐E, and ‐A satellites at ∼4 MLT in the outer magnetosphere. The magnetic and electric field oscillations at THEMIS were synchronized with the PMAAs. The magnetic energy of the THEMIS Pc5 oscillations is estimated using a numerical model of damped toroidal oscillations and compared with the kinetic energy of precipitating electrons associated with the field aligned current carried by the toroidal oscillations. The result reveals that the Pc5 magnetic energy is much larger than the kinetic energy, implying the magnetic energy is important for producing auroral emissions in the ionosphere. We also perform a simulation of the relationship between PMAAs and toroidal mode Pc5 oscillations. The simulation explains the observed spatial and temporal structures of the PMAAs. Plain Language Summary Aurora are a fascinating phenomenon observed in the polar region of the earth. The auroral emission is caused by the excitation of neutral oxygen atoms and nitrogen molecules in the ionosphere through collision with precipitating electrons from higher altitudes traveling along the magnetic field lines. The precipitating electrons need to have energies of order keV in order to produce auroral emissions. The energy is higher than that of solar wind electrons even after they are heated on passing through the bow shock in front of the magnetosphere. However, how the electrons gain the required high energy is not fully understood. The present study discusses a possible mechanism for the electron acceleration through analysis of the relationship between periodic auroral brightenin