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Auroral, Ionospheric and Ground Magnetic Signatures of Magnetopause Surface Modes
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  • Martin Owain Archer,
  • Michael D. Hartinger,
  • Lutz Rastatter,
  • David J. Southwood,
  • Michael Heyns,
  • Joseph William Brenig Eggington,
  • Andrew N. Wright,
  • Ferdinand Plaschke,
  • Xueling Shi
Martin Owain Archer
Imperial College London

Corresponding Author:m.archer10@imperial.ac.uk

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Michael D. Hartinger
Space Science Institute
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Lutz Rastatter
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David J. Southwood
Blackett Laboratory, Imperial College
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Michael Heyns
Imperial College London
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Joseph William Brenig Eggington
Imperial College London
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Andrew N. Wright
University of St Andrews
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Ferdinand Plaschke
Institut für Geophysik und extraterrestrische Physik, TU Braunschweig
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Xueling Shi
Virginia Polytechnic Institute and State University
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Surface waves on Earth’s magnetopause have a controlling effect upon global magnetospheric dynamics. Since spacecraft provide sparse in situ observation points, remote sensing these modes using ground-based instruments in the polar regions is desirable. However, many open conceptual questions on the expected signatures remain. Therefore, we provide predictions of key qualitative features expected in auroral, ionospheric, and ground magnetic observations through both magnetohydrodynamic theory and a global coupled magnetosphere-ionosphere simulation of a magnetopause surface eigenmode. These show monochromatic oscillatory field-aligned currents, due to both the surface mode and its non-resonant Alfvén coupling, are present throughout the magnetosphere. The currents peak in amplitude at the equatorward edge of the magnetopause boundary layer, not the open-closed boundary as previously thought. They also exhibit slow poleward phase motion rather than being purely evanescent. We suggest the upward field-aligned current perturbations may result in periodic auroral brightenings. In the ionosphere, convection vortices circulate the poleward moving field-aligned current structures. Finally, surface mode signals are predicted in the ground magnetic field, with ionospheric Hall currents rotating perturbations by approximately (but not exactly) 90º compared to the magnetosphere. Thus typical dayside magnetopause surface modes should be strongest in the East-West ground magnetic field component. Overall, all ground-based signatures of the magnetopause surface mode are predicted to have the same frequency across L-shells, amplitudes that maximise near the magnetopause’s equatorward edge, and larger latitudinal scales than for field line resonance. Implications in terms of ionospheric Joule heating and geomagnetically induced currents are discussed.