Midnight sector observations of auroral omega bands

Wild, J. A.; Woodfield, E. E.; Donovan, E.; Fear, R. C.; Grocott, Adrian; Lester, M.; Fazakerley, A. N.; Lucek, E.; Khotyaintsev, Yuri V.; André, Mats; Kadokura, Akira; Hosokawa, K.; Carlson, C. W.; McFadden, J. P.; Glaßmeier, K.‐H.; Angelopoulos, V.; Björnsson, G.

doi:10.1029/2010ja015874

Cited by 23 publications

(42 citation statements)

References 55 publications

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“…With the T96 model we can indeed map the flow shears to this downtail region (Table S1). This region is close to the previously suggested source region of omega bands (Jorgensen et al, ; Wild et al, ). Therefore, it is unlikely that the shear is between the plasma sheet flow and the LLBL flow, because LLBL flow is not expected to penetrate to the inner edge of the plasma sheet.…”

Section: Summary and Discussioncontrasting

confidence: 97%

Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI

Liu

Lyons

Archer

et al. 2018

Geophysical Research Letters

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Omega bands are curved aurora forms that evolve from a quiet arc located along the poleward edge of a diffuse auroral band within the midnight to morningside auroral oval. They usually propagate eastward. Because omega bands are a significant contributor to an active magnetotail, knowledge about their generation is important for understanding tail dynamics. Previous studies have shown that auroral streamers, footprints of fast flows in the tail, can propagate into omega bands. Such events, however, are limited, and it is still unclear whether and how the flows trigger the bands. The ionospheric flows associated with omega bands may provide valuable information on the driving mechanisms of the bands. We examine these flows taking advantage of the conjunctions between the Swarm spacecraft and Time History of Events and Macroscale Interactions during Substorms all‐sky imagers, which allow us to demonstrate the relative location of the flows to the omega bands' bright arcs for the first time. We find that a strong eastward ionospheric flow is consistently present immediately poleward of the omega band's bright arc, resulting in a sharp flow shear near the poleward boundary of the band. This ionospheric flow shear should correspond to a flow shear near the inner edge of the plasma sheet. This plasma sheet shear may drive a Kelvin‐Helmholz instability which then distorts the quiet arc to form omega bands. It seems plausible that the strong eastward flows are driven by streamer‐related fast flows or enhanced convection in the magnetotail.

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Section: Summary and Discussioncontrasting

confidence: 97%

Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI

Liu

Lyons

Archer

et al. 2018

Geophysical Research Letters

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“…The combined upward and downward current regions covered less than 1 MLT which corresponds to 560 km in the ionosphere at 70° ILAT, with the upward current regions covering between 80 km and 340 km in MLT and the structures appeared to move eastward at 0.8 km s −1 . These scale sizes and eastward motion, along with the apparent rotation of the upward current sheets, are consistent with previous observations of auroral omega bands [ Opgenoorth et al , 1983; Wild et al , 2000, 2011]. These features are commonly seen toward the end of a substorm and our observations are consistent with this.…”

Section: Discussionsupporting

confidence: 93%

Temporal evolution and electric potential structure of the auroral acceleration region from multispacecraft measurements

Forsyth¹,

Fazakerley²,

Walsh³

et al. 2012

J. Geophys. Res.

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[1] Bright aurorae can be excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modeling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest that particle acceleration occurs throughout this region. Using multispacecraft observations from Cluster, we have examined two upward current regions on 14 December 2009. Our observations show that the potential difference below C4 and C3 changed by up to 1.7 kV between their respective crossings, which were separated by 150 s. The field-aligned current density observed by C3 was also larger than that observed by C4. The potential drop above C3 and C4 was approximately the same in both crossings. Using a novel technique of quantitively comparing the electron spectra measured by Cluster 1 and 3, which were separated in altitude, we determine when these spacecraft made effectively magnetically conjugate observations, and we use these conjugate observations to determine the instantaneous distribution of the potential drop in the AAR. Our observations show that an average of 15% of the potential drop in the AAR was located between C1 at 6235 km and C3 at 4685 km altitude, with a maximum potential drop between the spacecraft of 500 V, and that the majority of the potential drop was below C3. Assuming a spatial invariance along the length of the upward current region, we discuss these observations in terms of temporal changes and the vertical structure of the electrostatic potential drop and in the context of existing models and previous single-and multispacecraft observations. Citation: Forsyth, C., et al. (2012), Temporal evolution and electric potential structure of the auroral acceleration region from multispacecraft measurements,

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“…Before 0049 UT, Poynting flux had no significant variations (less than 0.01 mW/m 2 ), but it was obviously enhanced after 0049 UT, i.e., during the interval in which the eastward drifting FACs would pass over CL1. The peak value of the enhanced Poynting flux at CL1 exceeded 0.01 mW/m 2 , which was no more than the half of Poynting flux in the plasma sheet ∼8 R E tailward of the Earth [ Wild et al , 2011]. Just during the Poynting flux enhancements, the parallel and anti‐parallel electron DEFs were also slightly enhanced.…”

Section: Discussionmentioning

confidence: 99%

“…Their results suggested that the magnetospheric counterpart of omega bands/Ps6 pulsations originates from a localized region in the near‐Earth magnetotail. A recent study by Wild et al [2011] compared the ground‐based all‐sky imager measurements of omega bands with the in situ field and plasma measurements form the conjugate region in the near‐Earth magnetotail. Although they did not find a clear one‐to‐one correspondence between variations in the ionosphere and magnetosphere, they suggested that that Alfvén waves in the plasma sheet ∼8 R E tailward of the Earth are responsible for the generation of FACs that cause omega bands/Ps6 pulsations observed on the ground.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous ground‐satellite observations of meso‐scale auroral arc undulations

Motoba¹,

Hosokawa²,

Ogawa³

et al. 2012

J. Geophys. Res.

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[1] We present simultaneous ground-based and in situ measurements of a train of meso-scale (about 100-300 km) auroral arc undulations, occurring in the postmidnight sector ($1 MLT) between 0040 UT and 0054 UT on September 21, 2009. The undulations appeared at the auroral poleward boundary, and then moved eastward with a speed of 0.9-2.2 km s À1 . Dynamic behaviors of the associated meso-scale ionospheric plasma flows and current systems were also detected with the ground-based magnetometer and radar measurements within the all-sky camera field-of-view. During the interval of interest, simultaneous Cluster observations in the central near tail region (11-14 R E down tail) were available, and especially the ionospheric footprint of Cluster 2 (CL2) was close to the optical auroral forms. CL2 observed strong fluctuations in the in situ magnetic field with amplitude of 5-10 nT whenever a bright arc area, and its trailing adjacent area, of the auroral undulations passed its ionospheric footprint. Such in situ magnetic field changes at CL2 could be considered as a manifestation of localized upward and downward field-aligned current sheets moving eastward at the central near-Earth tail boundary, linked to the meso-scale auroral undulation structures.

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Midnight sector observations of auroral omega bands

Cited by 23 publications

References 55 publications

Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI

Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI

Temporal evolution and electric potential structure of the auroral acceleration region from multispacecraft measurements

Simultaneous ground‐satellite observations of meso‐scale auroral arc undulations

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