Small-scale structure on the poleward edge of a stable auroral red arc

Nicolls, M. J.; Kelley, M. C.; Erdogan, C.

doi:10.1109/tps.2005.845008

Cited by 4 publications

(5 citation statements)

References 6 publications

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“…The variability types discussed included (a) longevity, (b) multiplicity, (c) zonal structure, (d) latitudinal inhomogeneity, and (e) tilt with respect to geomagnetic coordinates. Several of these features were pointed out in earlier publications by our group and by observations made by others at different locations [ Rees and Roble , ; Craven et al ., ; Kozyra et al ., ; Nicolls et al ., ]. The occurrence of all five types in the data archive for a single site (Millstone Hill) suggested that the stability term used in the phenomenon's definition needed to be reassessed.…”

Section: Observationsmentioning

confidence: 99%

“…In this paper we present images of the SAR arc of 2 October 2013 that exhibited multiple patches of emission with peak brightness values of ~ 800 R upon a background arc of ~300 R. Equatorward of the SAR arc, the airglow at zenith above Millstone Hill was ~120 R. Most unusual were concurrent observations of atomic oxygen emission at 5577 Å that revealed a similar morphology of patches (with a red to green brightness ratio of ~40) but without the unambiguous presence of a uniform background arc. Prior reports of structures within a SAR arc have appeared in the literature [ Craven et al ., ; Mendillo et al ., ; Foster et al ., ; Semeter et al ., ; Nicolls et al ., ]. Also in the literature are relatively rare cases of departures from spectral purity (see historical summaries of SAR arc characteristics in Rees and Roble []).…”

Section: Introductionmentioning

confidence: 99%

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A stable auroral red (SAR) arc with multiple emission features

et al. 2016

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Stable auroral red (SAR) arcs offer subvisible evidence for storm time linkages between the inner magnetosphere and the midlatitude ionosphere. A SAR arc's defining characteristics are horizon‐to‐horizon east‐west extent, a few degrees of latitude in meridional extent, emission only at the oxygen 6300 Å line, and minimal brightness changes during a night—effects readily provided by steady heat conduction from the ring current‐plasmapause interaction region. Here we describe a typical SAR arc (brightness ~300 rayleighs) with several superimposed patches of emission in two oxygen lines (with a 6300 Å/5577 Å ratio of ~40). We find no evidence for highly localized heating effects but rather evidence from GPS satellites supporting low‐energy electron precipitation as the SAR arc modulating mechanism. Seven brightness peaks with average longitude spacing of ~4° define a new spatial pattern for SAR arc studies.

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Section: Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A stable auroral red (SAR) arc with multiple emission features

et al. 2016

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“…Small scale structure on the poleward edge of SAR arc with an estimated brightness of ~1 kR was noted in Nicolls et al . [], and finally, Baumgardner et al . [2007] showed that such effects also occurred for the brightest event imaged to date.…”

Section: Discussionmentioning

confidence: 99%

“…The sources of these nonstable aspects of SAR arcs are not yet explained. Some may be due to plasma instabilities [ Nicolls et al ., ], while others to bursts of low energy precipitation; some may be due to enhanced T e values within fluxtubes experiencing transient surges in ring current strength or changes in ion populations. The modeling results in Kozyra et al .…”

Section: Discussionmentioning

confidence: 99%

“…The L values of the plasmapause/ring current interaction regions are clearly more tightly specified by the continuous optical data taken throughout the nighttime hours (in comparison to the DMSP T e peaks that mix dawn and dusk extreme values). In prior case studies of DMSP overflights of SAR arc locations [ Foster et al ., ; Nicolls et al ., ; Baumgardner et al ., , ], the latitude of the T e peak always coincided with the arc, and so the variability differences between Figures and are indicators of local time sampling effects, not fundamental differences between the two techniques.…”

Section: Electron Temperature Signatures Of Sar Arcsmentioning

confidence: 99%

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Imaging magnetospheric boundaries at ionospheric heights

et al. 2013

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[1] An all-sky imager (ASI) records atmospheric emissions from zenith to low on the horizon at all azimuths, a region typically spanning millions of square kilometers. Each pixel (with its unique elevation, azimuth, and emission height) can be mapped along B-field lines to the equatorial plane of the magnetosphere. Auroral and subauroral structures and boundaries seen in emission within the ionosphere-thermosphere (I-T) system can thus be related to source regions. For a midlatitude site, this I-T to inner magnetosphere connection typically falls within the L = 2-5 earth radii domain. In this study, we present the first case of a stable auroral red (SAR) arc observed from three widely spaced ASI sites (Europe, North America, New Zealand). SAR arcs are produced during the main and recovery phases of a geomagnetic storm, with emission driven by heat conduction from a very specific location in the magnetosphere-the L value where the plasmapause and the inner edge of the ring current overlap. Using three-site observations, we show that this boundary can be followed for 24 consecutive hours. Simultaneous observations made by three satellites in the Defense Meteorological Satellite Program (DMSP) show that the lowest latitude peak in electron temperature can be used to map the same boundary. A key structure of the inner magnetosphere that cannot be observed continuously from sensors orbiting within the magnetosphere is made continuously visible to ground-based optical systems via effects caused by the drainage of small amounts of ring current energy into the I-T system.

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SAR arcs we have seen: Evidence for variability in stable auroral red arcs

2016

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Since 1987, an all‐sky airglow imaging system has operated from a site at the Millstone Hill/Haystack Observatory in Westford, MA. During the ~2.5 solar cycles from 1987 to 2014, many studies using all‐sky images, in conjunction with incoherent scatter radar and satellite data, described subauroral, ionospheric disturbances observed during individual geomagnetic storms. The most prominent storm time optical feature from a subauroral site is a stable auroral red (SAR) arc. The standard use of a SAR arc's position is to locate the ionospheric footprint of the narrow plasmapause‐ring current interaction region where heat conduction from the inner magnetosphere excites emission within the F layer trough. When mapped from an emission altitude of 400 km to the geomagnetic equatorial plane, SAR arcs from Millstone Hill give the location of the plasmapause at radial distances between 2 to 4.5 Earth radii. A total of 314 SAR arcs have been observed during the 27 years of imaging at Millstone Hill. We find no single morphology for all SAR arcs, but rather patterns that occasionally depart from stability in space and time. We have classified these into five categories: longevity, multiplicity, zonal structure, latitudinal inhomogeneity, and tilt with respect to geomagnetic coordinates. In each case, the implications for the inner magnetosphere sources that drive SAR arcs are explored. While individual SAR arc variability characteristics have been noted in previous studies, here we describe for the first time all five types from the same site—an aspect not yet addressed in either magnetosphere or ionosphere modeling studies.

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Small-scale structure on the poleward edge of a stable auroral red arc

Cited by 4 publications

References 6 publications

A stable auroral red (SAR) arc with multiple emission features

A stable auroral red (SAR) arc with multiple emission features

Imaging magnetospheric boundaries at ionospheric heights

SAR arcs we have seen: Evidence for variability in stable auroral red arcs

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