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

Mishin, E. V.; Streltsov, A. V.

doi:10.1029/2019gl085446

Cited by 26 publications

(48 citation statements)

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“…The magnetic field elongation often observed in the green emissions adjacent to STEVE (e.g., Figure 1) has naturally led many to assume production via usual auroral mechanisms—that is, penetration of magnetospheric electrons with kinetic energy >1 keV (e.g., Gillies et al, 2019; Mishin & Streltsov, 2019; Nishimura et al, 2019). However, initial spectroscopic measurements reported by Gillies et al (2019) are inconsistent with this hypothesis.…”

Section: Discussionmentioning

confidence: 99%

The Mysterious Green Streaks Below STEVE

Semeter

Hunnekuhl²,

MacDonald

et al. 2020

AGU Advances

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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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Section: Discussionmentioning

confidence: 99%

The Mysterious Green Streaks Below STEVE

Semeter

Hunnekuhl²,

MacDonald

et al. 2020

AGU Advances

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“…It is reasonable to assume that the plasmapause moves inward due to erosion of the plasmasphere (e.g., Goldstein et al, ). Thus, according to Mishin and Streltsov (, Figure S4), the first postbreakup MPF will form the PS boundary and SAID (“1”) closer to the Earth, leaving the onset‐related (“O”) SAID outward/poleward to the new PS/auroral boundary. Note that SAID 1 peak is at the boundary alike that from RBSP‐B (Figure ) and F9 (Figure , frame 2).…”

Section: Fine Structure Of the Ps/auroral Boundarymentioning

confidence: 93%

Prebreakup Arc Intensification due to Short Circuiting of Mesoscale Plasma Flows Over the Plasmapause

Mishin

Streltsov

2020

JGR Space Physics

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The prebreakup arc at the inner edge of the auroral boundary is intensified upon arrival of an auroral streamer-the ionospheric signature of the earthbound mesoscale plasma flows (MPF). Yet the cause of electron precipitation enhancement only in this region remains unclear. We suggest that the intensified precipitation comes from the turbulent plasmasphere boundary layer (TPBL) that forms due to short circuiting of MPFs over the presubstorm plasmapause and overlaps with the plasma sheet (PS) inner boundary. Resonance interaction of the PS electrons with intense low-frequency plasma waves leads to enhanced precipitation from this narrow region. Indeed, the DMSP spacecraft observations near the substorm onset show intensified electron fluxes in a narrow region near the auroral boundary, which maps into the TPBL. The same pattern observed in conjunction with postonset auroral streamers points to the common mechanism, which is the short-circuiting process. Therefore, we suggest that the enhanced precipitation into the prebreakup arc is causally related to the MPFs' short circuiting over the plasmapause.We examine this problem using a concept of MPFs' short circuiting over the plasmapause (Mishin & Puhl-Quinn, 2007;Mishin et al., 2010Mishin, 2013) that explains the essential features of subauroral ion drifts (SAID). In this concept, low-ram pressure MPFs penetrate into the inner magnetosphe owing to the polarization field emerging at the forefront, as established in laboratory experiments (e.g., Brenning et al., 2005). This self-similar process breaks apart when the dense cold plasma at the presubstorm plasmapause shorts out the polarization charge. As a result, the MPF's (hot) electrons come to a halt hereby creating a steep, energy-independent PS/auroral boundary (cf. Newell & Meng, 1987), which is close to the prebreakup boundary owing to the steep density gradient at the plasmapause.The inflowing MPF's electrons pile up near the stopping point and create a narrow peak in the electron pressure, which creates the electron diamagnetic drift driving intense plasma turbulence (Mishin et al., 2010;Mishin & Sotnikov, 2017). Meanwhile, the MPF's ions move further inward until the nascent SAID electric field stops them. Thus, SAID inside of the plasmapause emerge just before the substorm breakup or pseudobreakup. Once created in the equatorial magnetosphere, the electric field propagates along the magnetic field into the ionosphere. That is, the plasmapause works as a power plant converting via short-circuiting the kinetic energy of MPFs into subauroral electromagnetic energy (Streltsov & Mishin, 2018).Most important for the purpose of this paper is that intense plasma waves develop in a narrow boundary layer (TPBL) enclosing the plasmapause around the MPF's stopping point (Mishin et al., 2010;Mishin, 2013). The TPBL overlaps with the PS inner edge, thence resonance wave-particle interactions cause enhanced precipitation into the prebreakup arc. This assumption is investigated in the rest of this paper using selected DMSP

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“…The magnetic field elongation often observed in the green emissions adjacent to STEVE (e.g., Figure 1) has naturally led many to assume production via usual auroral mechanisms-that is, penetration of magnetospheric electrons with kinetic energy 1 keV (e.g., Gillies et al, 2019;Mishin & Streltsov, 2019;Nishimura > et al, 2019). However, initial spectroscopic measurements reported by Gillies et al (2019) are inconsistent with this hypothesis.…”

Section: Source Of Green Line Excitationmentioning

confidence: 99%

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...

show abstract

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

Cited by 26 publications

References 50 publications

The Mysterious Green Streaks Below STEVE

The Mysterious Green Streaks Below STEVE

Prebreakup Arc Intensification due to Short Circuiting of Mesoscale Plasma Flows Over the Plasmapause

The Mysterious Green Streaks Below STEVE

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