The auroral distribution and its mapping according to substorm phase

Elphinstone, R. D.; Murphree, J. S.; Hearn, D. J.; Heikkila, W. J.; Henderson, M. G.; Cogger, L. L.; Sandahl, I.

doi:10.1016/0021-9169(93)90142-l

Cited by 39 publications

(46 citation statements)

References 51 publications

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“…7. The polar cap arc and the boundary of the teardrop-shaped polar cap can be mapped to the¯anks of the magnetosphere, the low latitude boundary layer (LLBL), while the lower latitude transient arcs are more probably associated with auroral activity originating in the magnetospheric plasma sheet (Elphinstone et al, 1993).…”

Section: Discussionmentioning

confidence: 99%

“…During IMF f z b 0 nT conditions the downward FAC region can extend to very high latitudes to form the horse-collar auroral structure of Hones et al, (1989). Indeed, the location and alignment of the observed arc is reminiscent of this horse-collar auroral con®guration and a teardrop-shaped polar cap (Murphree et al, 1982;Elphinstone et al, 1993), illustrated in Fig. 8a.…”

Section: Spatial Variation: High Latitude or Polar Arc Systemmentioning

confidence: 95%

“…In this interpretation, a velocity enhancement might be observed adjacent to and poleward of the optical arc. polar cap and sunward return¯ow at lower latitudes, is carried by upward-going thermal electrons i`100 eV) and is associated with the poleward diuse auroral region (Elphinstone et al, 1993). Embedded within this region is structured electron precipitation (0.1 to 1 keV) which produces sun-aligned polar arc phenomena (Yamamoto et al, 1993;Elphinstone et al, 1993).…”

Section: Spatial Variation: High Latitude or Polar Arc Systemmentioning

confidence: 99%

“…polar cap and sunward return¯ow at lower latitudes, is carried by upward-going thermal electrons i`100 eV) and is associated with the poleward diuse auroral region (Elphinstone et al, 1993). Embedded within this region is structured electron precipitation (0.1 to 1 keV) which produces sun-aligned polar arc phenomena (Yamamoto et al, 1993;Elphinstone et al, 1993). Feldstein et al (1995) employed Viking and DMSP satellite data to illustrate the case of a theta aurora associated with an overall downward FAC, but within which were embedded small-scale upward FACs of electron precipitation producing ®ne-structured optical emissions.…”

Section: Spatial Variation: High Latitude or Polar Arc Systemmentioning

confidence: 99%

“…8. a The horse-collar auroral con®guration (Hones et al, 1989) and teardrop-shaped polar cap (Elphinstone et al, 1993) proposed for northward IMF conditions; b Convection¯ow (Burch et al, 1992) and open and closed ®eld regions (Henderson et al, 1996) proposed for northward IMF conditions. The tongues of closed¯ux extending across the``polar cap'' are associated with convection reversals and hence polar cap aurora then, a manifestation of transient reconnection in the magnetotail and even a bursty bulk¯ow event (Angelopoulos et al, 1992).…”

Section: A1mentioning

confidence: 99%

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A comparison of optical and coherent HF radar backscatter observations of a post-midnight aurora

Milan

Lester

Moen³

1997

Ann. Geophys.

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Abstract. A poleward-progressing 630 nm optical feature is observed between approximately 0100 UT and 0230 UT (0400 MLT to 0530 MLT) by a meridianscanning photometer (MSP) located at Ny A Ê lesund, Svalbard. Simultaneous coherent HF radar measurements indicate a region of poleward-expanding backscatter with rapid sunward plasma¯ow velocity along the MSP meridian. Spatial maps of the backscatter indicate a stationary backscatter feature aligned obliquely with respect to the MSP meridian, which produces an impression of poleward-expansion as the MSP progresses to later MLT. Two interpretations of the observations are possible, depending on whether the arc system is considered to move (time-dependent) or to be stationary in time and apparent motion is produced as the MSP meridian rotates underneath it (timeindependent). The ®rst interpretation is as a poleward motion of an east-west aligned auroral arc. In this case the appearance of the region of backscatter is not associated with the optical feature, though the velocities within it are enhanced when the two are co-located. The second interpretation is as a polar arc or theta aurora, common features of the polar cap under the prevailing IMF northwards conditions. In this case the backscatter appears as an approximately 150 km wide region adjacent to the optical arc. In both interpretations the luminosity of the optical feature appears related to the magnitude of the plasma¯ow velocity. The optical features presented here do not generate appreciable HF coherent backscatter, and are only identi®able in the backscatter data as a modi®cation of the¯ow by the arc electrodynamics.

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Section: Discussionmentioning

confidence: 99%

Section: Spatial Variation: High Latitude or Polar Arc Systemmentioning

confidence: 95%

Section: Spatial Variation: High Latitude or Polar Arc Systemmentioning

confidence: 99%

Section: Spatial Variation: High Latitude or Polar Arc Systemmentioning

confidence: 99%

Section: A1mentioning

confidence: 99%

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A comparison of optical and coherent HF radar backscatter observations of a post-midnight aurora

Milan

Lester

Moen³

1997

Ann. Geophys.

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The quiet evening auroral arc and the structure of the growth phase near‐Earth plasma sheet

Coroniti

Pritchett

2014

JGR Space Physics

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The plasma pressure and current configuration of the near-Earth plasma sheet that creates and sustains the quiet evening auroral arc during the growth phase of magnetospheric substorms is investigated. We propose that the quiet evening arc (QEA) connects to the thin near-Earth current sheet, which forms during the development of the growth phase enhancement of convection. The current sheet's large polarization electric fields are shielded from the ionosphere by an Inverted-V parallel potential drop, thereby producing the electron precipitation responsible for the arc's luminosity. The QEA is located in the plasma sheet region of maximal radial pressure gradient and, in the east-west direction, follows the vanishing of the approximately dawn-dusk-directed gradient or fold in the plasma pressure. In the evening sector, the boundary between the Region1 and Region 2 current systems occurs where the pressure maximizes (approximately radial gradient of the pressure vanishes) and where the approximately radial gradient of the magnetic flux tube volume also vanishes in an inflection region. The proposed intricate balance of plasma sheet pressure and currents may well be very sensitive to disruption by the arrival of equatorward traveling auroral streamers and their associated earthward traveling dipolarization fronts.

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Stepwise tailward retreat of magnetic reconnection: THEMIS observations of an auroral substorm

et al. 2016

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Auroral stepwise poleward expansions were clarified by investigating a multiple‐onset substorm that occurred on 27 February 2009. Five successive auroral brightenings were identified in all‐sky images, occurring at approximately 10 min intervals. The first brightening was a faint precursor. The second brightening had a wide longitude; thus, it represented the Akasofu substorm onset. Other brightenings expanded poleward; thus, they were interpreted to be auroral breakups. These breakups occurred stepwise; that is, later breakups were initiated at higher latitudes. Corresponding reconnection signatures were studied using Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations between 8 and 24 RE down the magnetotail. The Akasofu substorm onset was not accompanied by a clear reconnection signature in the tail. In contrast, the three subsequent auroral breakups occurred simultaneously (within a few minutes) with three successive fast flows at 24 RE; thus, these were interpreted to be associated with impulsive reconnection episodes. These three fast flows consisted of a tailward flow and two subsequent earthward flows. The flow reversal at the second breakup indicated that a tailward retreat of the near‐Earth reconnection site occurred during the substorm expansion phase. In addition, the earthward flow at the third breakup was consistent with the classic tailward retreat near the end of the expansion phase; therefore, the tailward retreat is likely to have occurred in a stepwise manner. We interpreted the stepwise characteristics of the tailward retreat and poleward expansion to be potentially associated by a stepwise magnetic flux pileup.

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The auroral distribution and its mapping according to substorm phase

Cited by 39 publications

References 51 publications

A comparison of optical and coherent HF radar backscatter observations of a post-midnight aurora

A comparison of optical and coherent HF radar backscatter observations of a post-midnight aurora

The quiet evening auroral arc and the structure of the growth phase near‐Earth plasma sheet

Stepwise tailward retreat of magnetic reconnection: THEMIS observations of an auroral substorm

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