A magnetospheric generator driving ion and electron acceleration and electric currents in a discrete auroral arc observed by Cluster and DMSP

Echim, Marius; Maggiolo, Romain; Roth, M.; Keyser, Johan De

doi:10.1029/2009gl038343

Cited by 24 publications

(38 citation statements)

References 17 publications

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“…Stronger converging fields lead to higher parallel potential differences, stronger upward field-aligned currents, even higher ionospheric conductivity, and accelerated upgoing ions, all typical of discrete auroral arcs (e.g. Lyons, 1981;Carlson et al, 1998;Vaivads et al, 2003;Figueiredo et al, 2005;Liléo et al, 2008;Echim et al, 2009). A statistical study by Johansson et al (2007) points out that the scale sizes of intense electric field signatures, of the field-aligned currents, and of the density gradients observed above the auroral zone at 5-7 R E geocentric distance were compatible, supporting the overall picture of a magnetospheric interface associated with the arc structure, and determining its thickness.…”

Section: Discussionmentioning

confidence: 99%

“…Such a current limiting effect may play a role in the generator; depending on the generation mechanism, there may be limitations to the maximum current that can be produced. If the generator is a plasma interface (Roth et al, 1993;De Keyser, 1999;Echim et al, 2007Echim et al, , 2009, there must be a current I G across the sheet, which could be produced by cross-field diffusion or by a small normal magnetic field component (De Keyser, 1999). A current limiting effect might also apply to ionospheric electrons.…”

Section: Current-voltage Relationsmentioning

confidence: 99%

“…It has by now been fairly well established that a magnetospheric interface that is coupled to the ionosphere may produce auroral phenomena (e.g., Roth et al, 1993;De Keyser, 1999;Johansson et al, 2006;Echim et al, 2007Echim et al, , 2009. Such an interface often implies strong changes in the magnetospheric plasma properties and thus a change in Knight's constant.…”

Section: Imprint Of Magnetospheric Plasma Variationsmentioning

confidence: 99%

“…Such a magnetospheric potential arises when an inner shear flow region is embedded in the broader magnetospheric convection pattern, or it can be produced by the microphysics at the center of a shear flow layer (e.g., Echim et al, 2009). Consider again the constant conductivity case with boundary conditions dφ(±∞)/dx = ± out and dφ(0)/dx = 0.…”

Section: Role Of the Magnetospheric Electric Potentialmentioning

confidence: 99%

“…The generator must be able to sustain the magnetospheric electric fields on a time scale that is long enough to set up the ionospheric configuration. It has been argued that, for instance, discrete arcs and subauroral ion drift layers are indeed powered by such magnetospheric generators (e.g., Roth et al, 1993;De Keyser et al, 1998;Echim et al, 2007Echim et al, , 2009. Although one cannot exclude the possibility of an ionospheric generator, as might be the case for polar cap arcs and theta aurorae (Zhu et al, 1993(Zhu et al, , 2005, that situation is not considered here.…”

Section: Introductionmentioning

confidence: 98%

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Auroral and sub-auroral phenomena: an electrostatic picture

Keyser

Echim

2010

Ann. Geophys.

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Abstract. Many auroral and sub-auroral phenomena are manifestations of an underlying magnetosphere-ionosphere coupling. In the electrostatic perspective the associated auroral current circuit describes how the generator (often in the magnetosphere) is connected to the load (often in the ionosphere) through field-aligned currents. The present paper examines the generic properties of the current continuity equation that characterizes the auroral circuit. The physical role of the various elements of the current circuit is illustrated by considering a number of magnetospheric configurations, various auroral current-voltage relations, and different types of behaviour of the ionospheric conductivity. Based on realistic assumptions concerning the current-voltage relation and the ionospheric conductivity, a comprehensive picture of auroral and sub-auroral phenomena is presented, including diffuse aurora, discrete auroral arcs, black aurora, and subauroral ion drift. The electrostatic picture of field-aligned potential differences, field-aligned currents, ionospheric electric fields and plasma drift, and spatial scales for all these phenomena is in qualitative agreement with observations.

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Section: Discussionmentioning

confidence: 99%

Section: Current-voltage Relationsmentioning

confidence: 99%

Section: Imprint Of Magnetospheric Plasma Variationsmentioning

confidence: 99%

Section: Role Of the Magnetospheric Electric Potentialmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Auroral and sub-auroral phenomena: an electrostatic picture

Keyser

Echim

2010

Ann. Geophys.

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Field‐aligned currents during the extreme solar minimum between the solar cycles 23 and 24

et al. 2014

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The solar minimum between solar cycles 23 and 24 was unusually long and deep. The upward region-1 (R1) field-aligned current (FAC) response to this extreme solar minimum was investigated using Defense Meteorological Satellite Program observations. The solar cycle responses on the dayside are different than those on the nightside. The field-aligned current density (J // ) on the dayside, at 12-17 magnetic local time (MLT), peaks in the declining phase of the solar cycle, in 2003, when the solar wind speed also peaks, whereas J // on the nightside, at 18-23 MLT, appears insensitive to the solar cycle. In 1995-2010, J // at 15-17 MLT reaches the lowest value during the extreme solar minimum in 2009, when the solar wind speed also reaches the lowest value. At 12-17 MLT, R1 is located mostly on open field lines or at the boundary layer, where the current is driven mostly by the velocity shear at the magnetopause boundary. However, on the nightside, R1 is located mostly on the closed field lines where J // is not driven directly and immediately by the solar wind. The nightside current width (Λ) exhibits a solar cycle effect such that Λ is smaller at the solar minimum and smallest in 2009. However, the dayside Λ exhibits little solar cycle effect. As a result, the FAC intensity (latitudinally integrated J // ) exhibits a solar cycle variation at all local times and the FAC intensity is lower during the extreme solar minimum than that of the previous solar minimum.

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Substorm simulation: Quiet and N‐S arcs preceding auroral breakup

Ebihara

Tanaka

2016

JGR Space Physics

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Auroral breakup at the onset of substorm expansion is sometimes preceded by auroral forms known as quiet arcs and N‐S arcs. Observations have shown that both the auroral forms tend to move equatorward, and the initial brightening takes place in or near one of the quiet arcs. The auroral forms attract great attention, but generation of auroral forms and their association with the initial brightening are poorly understood. Recent global magnetohydrodynamic simulations are capable of producing upward field‐aligned currents (FACs) that resemble the auroral forms in both shape and temporal evolution. Based on the simulation results, we propose the following scenarios: (1) When the convection electric field is weak (northward interplanetary magnetic field (IMF)), the high‐pressure region is elongated from the plasma sheet toward higher latitudes and is structured by a coupling between the magnetosphere and the ionosphere (interchange‐like instabilities). (2) When the convection electric field is strong (southward IMF), the structured high‐pressure region moves equatorward (toward the plasma sheet). Upward currents are generated around it, which can be observed as arcs in the ionosphere. The upward current can be tentatively intensified in the course of the equatorward movement before the formation of a near‐Earth neutral line (NENL). (3) The NENL releases magnetic tension and results in the enhancement of plasma pressure at off‐equator in the near‐Earth region. Sudden formation of the off‐equatorial high‐pressure region generates the onset current system that manifests initial brightening. Our scenario can explain the observational fact that poleward arcs remained undisturbed at the onset.

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A magnetospheric generator driving ion and electron acceleration and electric currents in a discrete auroral arc observed by Cluster and DMSP

Cited by 24 publications

References 17 publications

Auroral and sub-auroral phenomena: an electrostatic picture

Auroral and sub-auroral phenomena: an electrostatic picture

Field‐aligned currents during the extreme solar minimum between the solar cycles 23 and 24

Substorm simulation: Quiet and N‐S arcs preceding auroral breakup

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