Solving the auroral-arc-generator question by using an electron beam to unambiguously connect critical magnetospheric measurements to auroral images

• Published in: Journal of atmospheric and solar-terrestrial physics 2020-09, Vol.206, p.105310, Article 105310
• Main Authors: Borovsky, Joseph E., Delzanno, Gian Luca, Dors, Eric E., Thomsen, Michelle F., Sanchez, Ennio R., Henderson, Michael G., Marshall, Robert A., Gilchrist, Brian E., Miars, Grant, Carlsten, Bruce E., Storms, Steven A., Holloway, Michael A., Nguyen, Dinh
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Active experiments; Aurora; Auroral arcs; Electron beams; Magnetosphere-ionosphere coupling; Plasma physics
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2020.105310

An active mapping mission is described that unambiguously connects measurements in the Earth's magnetosphere to visible aurora in the atmosphere. The core of the mission is an electron-beam source operated on a spacecraft in the equatorial magnetosphere, with the electron beam traveling along the Earth's magnetic-field lines to the atmosphere, depositing its energy to create an optical beam-spot in the atmosphere at the footpoint of the spacecraft's magnetic-field line. This optical spot can be imaged by ground-based cameras, putting the location of the spacecraft's magnetic footpoint into the context of the optical aurora. Scientific instruments carried on the spacecraft make critical measurements of the properties of the magnetosphere at the locations where the magnetosphere powers the aurora, allowing the determination of the plasma-physics mechanisms by which the magnetosphere drives the aurora, in particular answering the outstanding question of how the magnetosphere drives low-latitude auroral arcs. Long-standing questions in magnetosphere-ionosphere coupling that have not been answered because we could not unambiguously connect locations in the magnetosphere with their image in the ionosphere will finally be addressed. In this paper the properties of a “standard” growth-phase auroral arc are collected, theories of the magnetospheric generation of auroral arcs are reviewed, and critical magnetospheric measurements to discern the mechanisms that drive auroral arcs are determined. Further, the plasma physics of the experiment is investigated, including spacecraft-charging mitigation, beam stability, beam scattering, and electron orbit theory. Tradeoffs (keV versus MeV) concerning the energy of the electron beam are enumerated. •A space experiment is designed to connect magnetospheric measurements to the aurora.•The science focus is the generator mechanisms of auroral arcs.•A standard growth-phase auroral arc is described.•Magnetospheric measurement requirements are listed.•Technical issues with the experiment are examined.