Steve: The Optical Signature of Intense Subauroral Ion Drifts

Archer, William; Gallardo‐Lacourt, B.; Perry, G. W.; St.-Maurice, J.-P.; Buchert, Stephan; Donovan, E.

doi:10.1029/2019gl082687

Cited by 63 publications

(122 citation statements)

References 42 publications

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“…Gallardo‐Lacourt et al () related various properties of the observed STEVEs to the general state of the Earth's geomagnetic environment and reinforced the relationship of STEVE occurrence in conditions favorable for SAIDs. A recent study by Archer et al () confirmed this association by examining 122 SAID occurrences, finding that STEVE occurred only for the most intense SAIDs, namely, those with large plasma velocities, high electron temperatures, and low electron densities.…”

Section: Introductionmentioning

confidence: 85%

Subauroral Green STEVE Arcs: Evidence for Low‐Energy Excitation

Mende

Harding

Turner

2019

Geophysical Research Letters

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Subauroral emissions known as STEVEs (Strong Thermal Emission Velocity Enhancements) are sometimes accompanied by green arcs containing magnetic field‐aligned “picket fence” structures. In a newly published spectrum of a green picket fence arc Gillies et al. (2019, https://doi.org/10.1029/2019GL083272) showed that the visible emission in such arcs is mostly OI 557.7 nm with minimal N2+ 1N. This finding is consistent with the color ratios found in digital camera photos (Mende & Turner, 2019, https://doi.org/10.1029/2019JA026851) and is distinct from the ratios in auroral precipitation. The spectrum also contains intense N2 first positive (1P) emission. The presence of OI 557.7 (~4.19 eV excitation energy) and N2 1P (~7.35 eV), combined with the lack of N2+ first negative (~18.75 eV) commonly seen in the aurora, suggests that the particles exciting the emission have energy <18.75 eV. This is strong evidence against the precipitation hypothesis recently put forth (Nishimura et al., 2019, https://doi.org/10.1029/2019GL082460; Gillies et al., 2019, https://doi.org/10.1029/2019GL083272).

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Section: Introductionmentioning

confidence: 85%

Subauroral Green STEVE Arcs: Evidence for Low‐Energy Excitation

Mende

Harding

Turner

2019

Geophysical Research Letters

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“…SAR arcs are found inside plasma density troughs of

n_{e} \sim 3 \times 1 0^{4}

^{- 3}

and

T_{e} \sim false(3 \div 5 false) \times 1 0^{3}

K related to subauroral polarization streams (SAPS) with flow speeds

v_{d} \sim 0.5

–1 km/s (e.g., Foster et al, ; Förster et al, ; Baumgardner et al, ). The STEVE‐related SAID channels (MacDonald et al, ; Nishimura et al, ; Archer et al, ) have higher

T_{e}

up to

\sim 1 0^{4}

K, larger speeds,

v_{d} \sim 4

–6 km/s, and deeper troughs,

n_{e} < 1 0^{4}

^{- 3}

.…”

Section: On the Steve Spectrummentioning

confidence: 99%

“…Skyglow in the form of a narrow in magnetic latitude, east‐west‐aligned mauve “ribbon” and occasionally green rayed “Picket Fence” equatorward of the auroral zone was often reported by amateur photographers. MacDonald et al () have named the mauve arcs as Strong Thermal Emission Velocity Enhancement (STEVE) because of the relation to strong plasma streams – subauroral ion drifts (SAID), with highly elevated electron temperature,

T_{e} \geq 5000

K. Their features have been detailed by Gallardo‐Lacourt, Liang, et al (), Gallardo‐Lacourt, Nishimura, et al (), Nishimura et al (), and Archer, Gallardo‐Lacourt, et al (). In particular, Gallardo‐Lacourt, Nishimura, et al () statistical study shows that STEVE occurred during the recovery phase of substorms.…”

Section: Introductionmentioning

confidence: 99%

STEVE and the Picket Fence: Evidence of Feedback‐Unstable Magnetosphere‐Ionosphere Interaction

Mishin

Streltsov

2019

Geophysical Research Letters

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This paper aims to extend the understanding of Strong Thermal Emission Velocity Enhancement (STEVE) and the Picket Fence related to strong subauroral ion drifts (SAID). We numerically demonstrated that precipitating energetic electrons are critical for the structuring of the Picket Fence. It is created by feedback-unstable magnetosphere-ionosphere interactions driven by the SAID electric field when the Hall conductance created by energetic (≥1 keV) electrons exceeds the Pedersen conductance. We show that thermal excitation of the red-line emission in STEVE is inhibited by inelastic collisions with molecular nitrogen. Suprathermal (≤500 eV) electrons coming from the turbulent plasmasphere appear to be the major source. We also show that the chemiluminescencent and radiative attachment reactions do not explain the short-wavelength part of the STEVE continuum and argue that accounting for vibrational excitation may resolve the problem. Atmosphere's upwelling due to enhanced ion-neutral drag leads to the increased abundance of molecular components relative to atomic oxygen.

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“…Recently, the strong thermal emission velocity enhancement (STEVE) has been found to be a subauroral optical feature associated with SAID with larger magnitudes than average SAID (Archer et al, 2019; MacDonald et al, 2018). Since plasma flow measurements are often limited in space and time, the optical signature can be useful for finding when and where intense SAID exist.…”

Section: Introductionmentioning

confidence: 99%

Magnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field‐Aligned Currents

et al. 2020

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To understand magnetosphere‐ionosphere conditions that result in thermal emission velocity enhancement (STEVE) and subauroral ion drifts (SAID) during the substorm recovery phase, we present substorm aurora, particle injection, and current systems during two STEVE events. Those events are compared to substorm events with similar strength but without STEVE. We found that the substorm surge and intense upward currents for the events with STEVE reach the dusk, while those for the non‐STEVE substorms are localized around midnight. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations show that location of particle injection and fast plasma sheet flows for the STEVE events also shifts duskward. Electron injection is stronger and ion injection is weaker for the STEVE events compared to the non‐STEVE events. SAID are measured by Super Dual Auroral Radar Network during the STEVE events, but the non‐STEVE events only showed latitudinally wide subauroral polarization streams without SAID. To interpret the observations, Rice Convection Model (RCM) simulations with injection at premidnight and midnight have been conducted. The simulations successfully explain the stronger electron injection, weaker ion injection, and formation of SAID for injection at premidnight, because injected electrons reach the premidnight inner magnetosphere and form a narrower separation between the ion and electron inner boundaries. We suggest that substorms and particle injections extending far duskward away from midnight offer a condition for creating STEVE and SAID due to stronger electron injection to premidnight. The THEMIS all‐sky imager network identified the east‐west length of the STEVE arc to be ~1900 km (~2.5 h magnetic local time) and the duration to be 1–1.5 h.

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Steve: The Optical Signature of Intense Subauroral Ion Drifts

Cited by 63 publications

References 42 publications

Subauroral Green STEVE Arcs: Evidence for Low‐Energy Excitation

Subauroral Green STEVE Arcs: Evidence for Low‐Energy Excitation

STEVE and the Picket Fence: Evidence of Feedback‐Unstable Magnetosphere‐Ionosphere Interaction

Magnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field‐Aligned Currents

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