Open AccessPoleward‐moving recurrent auroral arcs associated with impulse‐excited standing hydromagnetic waves
Author(s) -
Zhao HuaYu,
Zhou Xu-Zhi,
Liu Ying,
Zong Qiu-Gang,
Rankin Robert,
Wang YongFu,
Shi QuanQi,
Shen Xiao-Chen,
Ren Jie,
Liu Han,
Chen XingRan
Publication year - 2019
Publication title -
earth and planetary physics
Language(s) - English
Resource type - Journals
ISSN - 2096-3955
DOI - 10.26464/epp2019032
Subject(s) - physics , ionosphere , magnetosphere , geophysics , spacecraft , standing wave , impulse (physics) , excited state , solar wind , computational physics , plasma , astrophysics , astronomy , classical mechanics , atomic physics , optics , quantum mechanics
In Earth's high‐latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi‐periodically with a recurrence time of a few minutes. The validation of this scenario requires spacecraft observations of ultra‐low‐frequency hydromagnetic waves in the magnetosphere and simultaneous observations of poleward‐moving auroral arcs near the spacecraft footprints. Here we present the first observational evidence from the multi‐spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission and the conjugated all‐sky imager to support the scenario that standing hydromagnetic waves can generate the quasi‐periodic appearance of poleward‐moving auroral arcs. In this specific event, the observed waves were toroidal branches of the standing hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi‐spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (consistent with the distribution of magnetic field line eigenfrequencies), which indicates that the phase difference across latitudes would increase with time. As time proceeds, the enlarged phase difference corresponds to a lower propagation speed of the auroral arcs, which agrees very well with the ground‐based optical data.