Distinguishing Subauroral Ion Drifts From Birkeland Current Boundary Flows

Archer, William; Knudsen, D. J.

doi:10.1002/2017ja024577

Cited by 16 publications

(21 citation statements)

References 21 publications

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“…The FAC (shown in pink) when crossing the point of maximum T e for all cases was either positive, indicating a downward FAC, or near zero. However, in all cases the available Swarm measurements presented in Figure 1 match typical past SAID observations from ∼500 km altitude (Anderson et al, 1991;Archer & Knudsen, 2018;Spiro et al, 1979), and are all roughly colocated with occurrences of Steve. The EFI was turned on shortly after event a, and a 800-m/s flow channel was observed coincident with the midlatitude density trough on the subsequent orbit (1.5 hr later).…”

Section: Steve Measurements With Swarmsupporting

confidence: 73%

Steve: The Optical Signature of Intense Subauroral Ion Drifts

Archer

Gallardo‐Lacourt

Perry

et al. 2019

Geophysical Research Letters

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102

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Little is currently known about the optical phenomenon known as Steve. The first scientific publication on the subject suggests that Steve is associated with an intense subauroral ion drift (SAID). However, additional inquiry is warranted as this suggested relationship as it is based on a single case study. Here we present eight occurrences of Steve with coincident or near‐coincident measurements from the European Space Agency's Swarm satellites and show that Steve is consistently associated with SAID. When satellite observations coincident with Steve are compared to that of typical SAID, we find the SAID associated with Steve to have above average peak ion velocities and electron temperatures, as well as extremely low plasma densities.

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Section: Steve Measurements With Swarmsupporting

confidence: 73%

Steve: The Optical Signature of Intense Subauroral Ion Drifts

Archer

Gallardo‐Lacourt

Perry

et al. 2019

Geophysical Research Letters

Self Cite

102

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“…In addition, we have compared the AL index observed during STEVE with subauroral ion drift (SAID) events identified by Archer and Knudsen () in Swarm satellite measurements. Swarm is a constellation of three satellites designed to study the dynamics of the Earth's magnetic field and its interactions with the Earth's system (Olsen et al, ).…”

Section: Data Set and Methodologymentioning

confidence: 99%

“…STEVE has been identified in the subauroral region by MacDonald et al (). In their study STEVE was colocated with a narrow and very fast flow (almost 6 km/s), which could correspond to an extreme SAID event (Archer & Knudsen, ; Spiro et al, ). For comparison, Figure b shows the superposed epoch analysis of the AL index for the 22 SAID events identified by Archer and Knudsen () using Swarm satellite.…”

Section: Solar Wind Conditions and Geomagnetic Activity Indicesmentioning

confidence: 96%

“…In their study STEVE was colocated with a narrow and very fast flow (almost 6 km/s), which could correspond to an extreme SAID event (Archer & Knudsen, ; Spiro et al, ). For comparison, Figure b shows the superposed epoch analysis of the AL index for the 22 SAID events identified by Archer and Knudsen () using Swarm satellite. In this plot, the red line indicates the average AL index and the vertical green dashed line corresponds to the time when the SAID fast and narrow flow signature was observed by the Swarm satellite.…”

Section: Solar Wind Conditions and Geomagnetic Activity Indicesmentioning

confidence: 96%

“… AL index superposed epoch analysis. (a) The 22 SAID (subauroral ion drift) events identified by Archer and Knudsen () and (b) SuperMAG substorm onset list, in the same format as Figure .…”

Section: Solar Wind Conditions and Geomagnetic Activity Indicesmentioning

confidence: 99%

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A Statistical Analysis of STEVE

et al. 2018

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There has been an exciting recent development in auroral research associated with the discovery of a new subauroral phenomenon called STEVE (Strong Thermal Emission Velocity Enhancement). Although STEVE has been documented by amateur night sky watchers for decades, it is as yet an unidentified upper atmosphere phenomenon. Observed first by amateur auroral photographers, STEVE appears as a narrow luminous structure across the night sky over thousands of kilometers in the east-west direction. In this paper, we present the first statistical analysis of the properties of 28 STEVE events identified using Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager and the Redline Emission Geospace Observatory (REGO) database. We find that STEVE occurs about 1 hr after substorm onset at the end of a prolonged expansion phase. On average, the AL index magnitude is larger and the expansion phase has a longer duration for STEVE events compared to subauroral ion drifts or substorms. The average duration for STEVE is about 1 hr, and its latitudinal width is~20 km, which corresponds to~¼ of the width of narrow auroral structures like streamers. STEVE typically has an equatorward displacement from its initial location of about 50 km and a longitudinal extent of 2,145 km. Plain Language Summary Strong Thermal Emission Velocity Enhancement (STEVE) is anatmospheric phenomenon that manifests across the night sky as an extremely thin yet long ribbon of vibrant purple and white hues. Although STEVE has been well documented by amateur auroral photographers for several decades, the scientific community only recently stumbled upon this phenomenon. In this paper, we report on the first statistical analysis of STEVE's optical characteristics using ground-based all-sky imagery and examined satellite data to determine the geomagnetic conditions favorable for the formation of STEVE. Our results verify that STEVE is narrow in the north-south direction, but it extends over a wider east-west region. We have also determined that STEVE displaces southward over its lifetime in most observations. More interestingly, all 28 STEVE events identified in this study were observed at the end of a prolonged substorm expansion phase. More recently, Gallardo-Lacourt et al. (2018) analyzed data from the Polar-Orbiting Environmental Satellite (POES)-17 satellite for one STEVE event identified by Time History of Events and Macroscale Interactions GALLARDO-LACOURT ET AL. 9893

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A time-dependent two-dimensional model simu- lation of lower ionospheric variations under in- tense SAID

Liang

St.-Maurice

Donovan

2021

Preprint

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The subauroral ion drift (SAID) denotes a latitudinally narrow channel of fast westward ion drift in the subauroral region, often observed during geomagnetically disturbed intervals. The recently recognized subauroral optical phenomena, the Strong Thermal Emission Velocity Enhancement (STEVE) and the Picket Fence, are both related to intense SAIDs. In this study, we present a 2D time-dependent model simulation of the self-consistent variations of the elec-tron/ion temperature, density, and FAC, under strong SAID, with more focus in the lower ionosphere. Our simulation reproduces many key features of SAID, such as the anomalous electron heating in the E-region, the strong electron temperature enhancement in the upper F-region, the intense ion frictional heating, and the plasma density depletion. Most importantly, the ion Pedersen drifts is found to play a crucial role in the density variations and FAC dynamics in the lower ionosphere. The transport effect of ion Pedersen drifts leads to strong density depletion in the lower ionosphere in a large portion of SAID. The FAC inside SAID is mainly downward with magnitude ï¿¿ ˜1 ï¿¿A/m 2. At the poleward edge of SAID, the ion Pedersen drift leads to a pileup of the plasma density and an upward FAC. Our simulation results also corroborate the presence of strong gradients of plasma density, temperature, and flows, at the edge of SAID, which may be conducive to certain plasma instabilities. Our model provides a useful tool for the future exploration of the generation mechanisms of STEVE and Picket Fence.

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Distinguishing Subauroral Ion Drifts From Birkeland Current Boundary Flows

Cited by 16 publications

References 21 publications

Steve: The Optical Signature of Intense Subauroral Ion Drifts

Steve: The Optical Signature of Intense Subauroral Ion Drifts

A Statistical Analysis of STEVE

A time-dependent two-dimensional model simu- lation of lower ionospheric variations under in- tense SAID

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