Electric fields and currents of stable drifting auroral arcs in the evening sector

Aikio, Anita; Lakkala, T.; Kozlovsky, Alexander; Williams, P. J. S.

doi:10.1029/2001ja009172

Cited by 62 publications

(68 citation statements)

References 39 publications

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“…Stauning (1984) explained the absorption event with values below 1.0 dB in the summer cusp by an enhanced classical collision frequency in the strongly heated E-region, in association with strong ionospheric electric fields exceeding 50 mV/m. This value of the electric field magnitude corresponds quite well to the experimentally determined "threshold" condition which should be met in order for strong electron heating to start operating Haldoupis et al, 1993;Aikio et al, 2002). It was also pointed out by Stauning (1984) that an event of this type requires a relatively dense E-region and substantially elevated electron temperatures to cause visible effects in the measured absorption.…”

Section: Discussionsupporting

confidence: 48%

“…The arc continued to drift equatorward until the substorm onset at 20:20 UT, when the arc intensified and a fold developed in the arc. The average drift speed of the arc was 120 m s −1 , and the width of the arc was 15 km (Aikio et al, 2002). Again, the region of CNA was located on the equatorward side of the arc, which can be seen from the bottom panel.…”

Section: Event 2 8 April 1998mentioning

confidence: 76%

“…We selected two good events: 7 December 1999 and 8 April 1998. In the latter event the auroral arc is associated with a region of enhanced electric field and increased T e in the E-region on the equatorward side of the arc, as discussed by Aikio et al (2002).…”

Section: Introductionmentioning

confidence: 92%

“…We argue that the T e enhancement is not related to the studied arc but to the arc on the poleward side of it, since the analysis of the electric field shows that at this location the northward electric field reaches a value of 50 mV m −1 and thus that arc obeys the typical electrodynamic pattern of some eveningside arcs (e.g. Aikio et al, 2002).…”

Section: Event 1 7 December 1999mentioning

confidence: 99%

“…Sergeev et al (1990) proposed that the observed CNA during a substorm growth phase was due to pitch-angle scattering of energetic electrons in the equatorial current sheet and the equatorward movement of the CNA region was due to configuration changes in the magnetotail. On the other hand, Williams et al (1990), Opgenoorth et al (1990), Aikio et al (1993) and Aikio et al (2002) have shown that an enhanced meridional electric field and an accompanying enhanced Eregion electron temperature are often observed outside of an auroral arc, on the equatorward side of an eveningside arc. In addition, there is evidence that CNA can occur outside of an arc and that the enhanced electric field associated with drifting quiet arc is also located outside of the arc.…”

Section: Introductionmentioning

confidence: 99%

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Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

et al. 2004

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Abstract. Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature (T e ) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced T e play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation.

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Section: Discussionsupporting

confidence: 48%

Section: Event 2 8 April 1998mentioning

confidence: 76%

Section: Introductionmentioning

confidence: 92%

Section: Event 1 7 December 1999mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

et al. 2004

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Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers

et al. 2014

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[1] Nightside auroral zone localized flow channels, typically associated with auroral poleward boundary intensifications and streamers, are an important component of high-latitude ionospheric plasma dynamics. We investigate the structure of these flow channels using two-dimensional line-of-sight flow observations from the Super Dual Auroral Radar Network (SuperDARN) radars and auroral images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground-based all-sky imager (ASI) array. Radar echoes captured <~500 km horizontal distance from the radars were mainly used to detect small-scale flow structures that would otherwise be missed or poorly resolved in long-range radar echoes. After identifying 135 auroral streamers in the ASI images at close-radar capture locations, we examined the associated ionospheric flow data in the radar echoes. Flow bursts and streamers are invariably correlated in all events. The flow bursts are often directed equatorward and appear simultaneously with the streamers. Equatorward flows are located just to the east of the streamers. Less frequently (~10% of the time), a poleward flow enhancement was detected even when a streamer propagated equatorward, the poleward flow enhancement being located to the west of the auroral streamer, or to the east of the equatorward flow enhancement, consistently with the spatial relationship between flow shear and upward field-aligned currents in plasma sheet flow bursts. The azimuthal width of the flow channel is, on average,~75 km, and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is~57 km eastward. This study demonstrates the capability of radar-imager pairs for identifying the 2-D structure of localized flows associated with plasma sheet flow bursts.

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The influence of magnetic flux depletion on the magnetotail and auroral morphology during the substorm growth phase

Hsieh

Otto

2014

JGR Space Physics

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Key Points:• Midnight MFD is an efficient mechanism to generate a very thin current sheet • The MFD model is subject to the adiabatic constraint • The MFD causes the equatorward motion of field-aligned currents Abstract The substorm growth phase is characterized by the equatorward motion of the growth phase arc close to or even into the region of diffuse aurora characteristic for a dipolar magnetic field. The presented study examines changes of the near-Earth current sheet and of the mapping of magnetotail feature into the auroral ionosphere based on midnight magnetic flux depletion (MFD) in the near-Earth tail. Midnight MFD is caused by sunward convection to replenish magnetic flux that is eroded on the dayside by magnetic reconnection during periods of southward interplanetary magnetic field. The results demonstrate that MFD causes the formation of a very thin current sheet in the near-Earth tail. It is found that the removal of magnetic flux in the near-Earth tail causes a contraction of the ionospheric footpoints of this tail region such that all of the mapped magnetotail structures move equatorward by about 2 to 3 • . The thin current layer is mapped into the region where magnetic flux is strongly depleted and in close proximity with strong and narrow regions 1 and 2 sense field-aligned currents. The ionospheric maps show a sharp transition between the dipole and stretched magnetic field and an evolution of thinning and convergent motion of field-aligned currents in the late growth phase. The results are obtained without loading of magnetic flux and energy into the tail lobes, demonstrating that many typical growth phase properties can be attributed to the depletion of near-Earth closed magnetic flux.

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Electric fields and currents of stable drifting auroral arcs in the evening sector

Cited by 62 publications

References 39 publications

Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers

The influence of magnetic flux depletion on the magnetotail and auroral morphology during the substorm growth phase

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