First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena

Gillies, D. M.; Donovan, E.; Hampton, Donald; Liang, J.; Connors, Martin; Nishimura, Y.; Gallardo‐Lacourt, B.; Spanswick, E.

doi:10.1029/2019gl083272

Cited by 68 publications

(152 citation statements)

References 17 publications

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“…The earlier high-elevation trace, though marginally perceptible, is too weak and without distinguishable optical counterpart on ASIs, so that it is not studied here. This result confirms the finding in Gillies et al (2019) that AGC constitutes the spectral characteristics of STEVE. See figure caption for all legend details.…”

Section: Spectral Characteristic Of Stevessupporting

confidence: 92%

“…Near the northern edge of the images there are some auroras. This observation offers evidence of the AGC nature of STEVE (Gillies et al, 2019). The more poleward brighter one represents the STEVE of interest, which was newly intensified after 0642 UT.…”

Section: Observational Geometry and Optical Features Of Interestmentioning

confidence: 59%

“…While the existence of night airglow continuum (AGC) has been known for decades (e.g., Barbier et al, 1951), their commonly reported AGC intensities in the existing literature (e.g., Sternberg & Ingham, 1972) are much weaker than that of STEVE (Gillies et al, 2019; and the fact that STEVE is visible to the naked eyes). While the existence of night airglow continuum (AGC) has been known for decades (e.g., Barbier et al, 1951), their commonly reported AGC intensities in the existing literature (e.g., Sternberg & Ingham, 1972) are much weaker than that of STEVE (Gillies et al, 2019; and the fact that STEVE is visible to the naked eyes).…”

Section: 1029/2019gl085639mentioning

confidence: 99%

“…Major optical instruments used in this study include the multiwavelength all-sky-imagers (ASIs) of the Athabasca University Geophysical Observatory (AUGSO) at Athabasca (54.60°N, 113.64°W), the Redline Emission Geospace Observatory (REGO), the Four-Eight-Six-One (FESO) photometer and the Transition Region Explorer Spectrograph (TRSp). TRSp is an imaging spectrograph designed to yield the optical spectra betweeñ 400 and 800 nm of night sky emissions at 0.4-nm resolution along a geographical meridian (Gillies et al, 2019). REGO is a 630-nm red-line imager (Liang et al, 2016).…”

Section: Observationsmentioning

confidence: 99%

“…Recently, Gillies et al (2019) reported an important finding based upon spectrograph measurements: STEVE contains an overall enhancement of a continuous spectrum spanning between~400 and 730 nm as its main ©2019. American Geophysical Union.…”

Section: Introductionmentioning

confidence: 99%

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Optical Spectra and Emission Altitudes of Double‐Layer STEVE: A Case Study

Liang

Donovan

Connors

et al. 2019

Geophysical Research Letters

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We report an event study of STEVE on 17 July 2018, with focus on the optical spectra and emission altitudes of STEVE. We find that the STEVE comprises two traces, one at a higher elevation angle and the other at a lower elevation angle. The two traces merge into one when viewed near the zenith. Spectrograph measurements show that both STEVE traces are characterized by enhancements over broadband wavelengths, that is, an airglow continuum, but they differ in their red-line (630 nm) component: The higher-elevation STEVE contains substantial red-line enhancement over background, while the lower-elevation STEVE does not. Based upon triangulation analyses using multiple optical instruments, we evaluate that the two STEVE traces are likely emitted from distinctly different altitudes: The higher-elevation STEVE comes from~250-km altitude, while the lower-elevation one is from ≤150-km altitude. Our results impose implications and constraints on the possible underlying mechanisms of STEVE. Plain Language SummaryThe recently discovered STEVE nightglow is active at times of auroral activity but does not seem to be an aurora. It is located at lower latitudes than the usual aurora, and as photographed on the citizen science cameras which played a large role in drawing attention to it, it has a different color. In this study, using a combination of scientific optical instruments, especially the spectrograph recently deployed at Lucky Lake, Canada, by the University of Calgary, we investigate the optical spectral properties of STEVE and their emission altitudes. Two major spectral (color) components of STEVE are identified. One is characterized by a broadband enhancement over the entire visible wavelength range, contributing to the apparently "whitish" color of the STEVE, and the other is contributed by oxygen airglow concentrated at 630 nm, adding a "reddish" tint to the STEVE. In the event occurring on 17 July 2018, the STEVE is found to comprise two emission structures originating from different altitudes, one at~250 km and the other at ≤150-km altitude. Both STEVE structures contain the white component but only the higher-altitude one shows a substantial red component. That red color is the same red as seen in auroras that come from high altitudes in the atmosphere, while the mechanism of the white component remains to be explored.

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Section: Spectral Characteristic Of Stevessupporting

confidence: 92%

Section: Observational Geometry and Optical Features Of Interestmentioning

confidence: 59%

Section: 1029/2019gl085639mentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optical Spectra and Emission Altitudes of Double‐Layer STEVE: A Case Study

Liang

Donovan

Connors

et al. 2019

Geophysical Research Letters

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Improved Analysis of STEVE Photographs

Bennett¹

2020

Preprint

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The Mysterious Green Streaks Below STEVE

Joshua

MacDonald

Hunnekuhl³

et al. 2020

Preprint

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Strong thermal emission velocity enhancement (STEVE) is an optical phenomenon of the subauroral 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 quasiperiodic 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-to 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 20-30 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.Plain Language Summary STEVE is a recently identified atmospheric phenomenon caused by supersonic plasma jets flowing at altitudes 100 km. STEVE appears as a whitish pink arc > extending in the magnetic east-west direction, which is often accompanied by an adjacent region of green features. In some cases, the green features appear as periodic vertical columns resembling a "picket fence". These features were thought to be caused by the same mechanism as the aurora, but the color is wrong. This article examines these features from a morphological perspective. We use time lapse images recorded by citizen scientists to examine fine-scale structures in STEVE's green emission region. We focus particular attention on a narrow streak of emission commonly observed underneath the picket fence. These streaks have width of just a few hundred meters and propagate horizontally. They have identical coloration to other green objects in the field, suggesting a common source. Although we cannot state conclusively what that source mechanism is, they are most likely excited by turbulent heating related to the extreme plasma flows of STEVE. Our initial analysis suggests a physical connection between these tiny streaks and the extended picket fence features above them. Advancing this physics will benefit greatly from continued involvement of citizen scien...

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First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena

Cited by 68 publications

References 17 publications

Optical Spectra and Emission Altitudes of Double‐Layer STEVE: A Case Study

Optical Spectra and Emission Altitudes of Double‐Layer STEVE: A Case Study

Improved Analysis of STEVE Photographs

The Mysterious Green Streaks Below STEVE

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