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The Mysterious Green Streaks Below STEVE
  • +4
  • Joshua Semeter,
  • Elizabeth A. MacDonald,
  • Michael Hunnekuhl,
  • Michael Hirsch,
  • Neil Zeller,
  • Alexei Chernenkoff,
  • Jun Wang
Joshua Semeter
Boston University, Boston University

Corresponding Author:[email protected]

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Elizabeth A. MacDonald
NASA Goddard Space Flight Center, NASA Goddard Space Flight Center
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Michael Hunnekuhl
Privat, Privat
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Michael Hirsch
SciVision, Inc., SciVision, Inc.
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Neil Zeller
Citizen scientist, Citizen scientist
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Alexei Chernenkoff
Citizen Scientist
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Jun Wang
Alberta Aurora Chasers
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Abstract

STEVE (Strong Thermal Emission Velocity Enhancement) is an optical phenomenon of the sub-auroral ionosphere arising from extreme ion drift speeds. STEVE consists of two distinct components in true-color imagery: a mauve or whitish arc extended in the magnetic east-west direction, and a region of green emission adjacent to the arc, often structured into quasi-periodic columns aligned with the geomagnetic field (the “picket fence”). This work employs high-resolution imagery by citizen scientists in a critical examination of fine scale features within the green emission region. Of particular interest are narrow “streaks” of emission forming underneath field-aligned picket fence elements in the 100–110-km altitude range. The streaks propagate in curved trajectories with dominant direction toward STEVE from the poleward side. The elongation is along the direction of motion, suggesting a drifting point-like excitation source, with the apparent elongation due to a combination of motion blur and radiative lifetime effects. The cross-sectional dimension is <1 km, and the cases observed have a duration of ~10–30 s. The uniform coloration of all STEVE green features in these events suggests a common optical spectrum dominated by the oxygen 557.7-nm emission line. The source is most likely direct excitation of ambient oxygen by superthermal electrons generated by ionospheric turbulence induced by the extreme electric fields driving STEVE. Some conjectures about causal connections with overlying field-aligned structures are presented, based on coupling of thermal and gradient-drift instabilities, with analogues to similar dynamics observed from chemical release and ionospheric heating experiments.
Dec 2020Published in AGU Advances volume 1 issue 4. 10.1029/2020AV000183