Monopolar and bipolar auroral electric fields and their effects

Keyser, Johan De; Maggiolo, Romain; Echim, Marius

doi:10.5194/angeo-28-2027-2010

Cited by 13 publications

(8 citation statements)

References 32 publications

(66 reference statements)

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“…Indeed, in a one‐dimensional planar interface (an assumption that is now known to be correct to within a few degrees of magnetic field tilt) in which time variations are slow (which is justified as well), Ampères Law states that In this way, the FACs can be computed. Figure 5d indicates z < 0 on the lobe side and z > 0 on the plasma sheet side of the structure, which agrees with the particle observations and also with the nature of the monopolar potential profile [ De Keyser et al , 2010]. Again, this computation differs from that of Johansson et al [2006, Figure 3], who do not account for boundary motion.…”

Section: Observations Of a Polar Cap Boundary Arcsupporting

confidence: 74%

“…Quasi‐stationary magnetosphere‐ionosphere coupling models are able to describe both large‐scale aurora [ Chiu and Schulz , 1978; Lyons , 1980; Chiu and Cornwall , 1980] and smaller‐scale discrete arcs [ Lyons , 1981; Echim et al , 2007, 2008; De Keyser and Echim , 2010; De Keyser et al , 2010]. These models are based on the concept of a DC electric circuit connecting a magnetospheric generator to an ionospheric load viafield‐aligned currents; changes in the auroral circuit produced by variations in the generator or by modifications of the ionospheric conductivity are considered to be rather slow.…”

Section: Introductionmentioning

confidence: 99%

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Wave signatures and electrostatic phenomena above aurora: Cluster observations and modeling

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[1] This paper reports Cluster high-altitude observations above the acceleration region of a typical monopolar electric field event at the plasma sheet boundary. The observations reveal both characteristics of waves and signatures of electrostatic acceleration. The observations can be interpreted in terms of low-frequency transverse magnetic waves on the auroral interface. A reconstruction of the spatial structure across the interface, effectively correcting for the slow oscillations of the interface, allows a proper determination of the electric potential and of the upward and downward currents. Because of the long wave period, the auroral system can be understood in terms of a quasi-electrostatic model. In this model, the precipitating plasma sheet particles induce a perpendicular heating of cold ionospheric H + and O + ions. As these ions escape from the ionosphere, their perpendicular motion is converted into parallel motion in the divergent geomagnetic field as a result of the conservation of magnetic moment. These ions acquire an additional parallel energy through acceleration by the magnetic-field-aligned electric field in the auroral acceleration region. They also may gain substantial perpendicular energy due to the perpendicular electric field, as theẼ ×B drift increases with altitude. Both types of acceleration are typical electrostatic phenomena.

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Section: Observations Of a Polar Cap Boundary Arcsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Wave signatures and electrostatic phenomena above aurora: Cluster observations and modeling

et al. 2011

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“…The U-or S-shaped potential drop produces the well known inverted-V structure in particle spectrograms, respectively for precipitating electrons at low altitude and for outflowing ions at high altitudes. An analytical quasi-stationary analysis has been recently proposed by De Keyser et al (2010). The downward quasi-static acceleration of electrons excites optical emissions in the ionosphere and leads to the formation of elongated and relatively stable discrete auroral arcs (e.g.…”

Section: Introductionmentioning

confidence: 99%

Polar cap ion beams during periods of northward IMF: Cluster statistical results

et al. 2011

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Abstract. Above the polar caps and during prolonged periods of northward IMF, the Cluster satellites detect upward accelerated ion beams with energies up to a few keV. They are associated with converging electric field structures indicating that the acceleration is caused by a quasi-static fieldaligned electric field that can extend to altitudes higher than 7 R E (Maggiolo et al., 2006;Teste et al., 2007).Using the AMDA science analysis service provided by the Centre de Données de la Physique des Plasmas, we have been able to extract about 200 events of accelerated upgoing ion beams above the polar caps from the Cluster database. Most of these observations are taken at altitudes lower than 7 R E and in the Northern Hemisphere.We investigate the statistical properties of these ion beams. We analyze their geometry, the properties of the plasma populations and of the electric field inside and around the beams, as well as their dependence on solar wind and IMF conditions. We show that ∼40 % of the ion beams are collocated with a relatively hot and isotropic plasma population. The density and temperature of the isotropic population are highly variable but suggest that this plasma originates from the plasma sheet. The ion beam properties do not change significantly when the isotropic, hot background population is present. Furthermore, during one single polar cap crossing by Cluster it is possible to detect upgoing ion beams both with and without an accompanying isotropic component.The analysis of the variation of the IMF B Z component prior to the detection of the beams indicates that the delay between a northward/southward turning of IMF and the appearance/disappearance of the beams is respectively ∼2 h and 20 min. The observed electrodynamic characteristics of high altitude polar cap ion beams suggest that they are closely connected to polar cap auroral arcs. We discuss the impliCorrespondence to: R. Maggiolo (romain.maggiolo@aeronomie.be) cations of these Cluster observations above the polar cap on the magnetospheric dynamics and configuration during prolonged periods of northward IMF.

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“…The source of the precipitating electron is expected to be in the high-altitude boundary layers, as predicted from a transport model along magnetic field lines. Finally, it is suggested that these acceleration structures could result from electrostatic potentials generated at the interface between the magnetopause boundary layers and the lobes [12][13].…”

Section: Discussionmentioning

confidence: 98%

CLUSTER observations of electrostatic acceleration structures above the polar cap and implications for their origin in the magnetopause boundary layer

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2011

2011 XXXth URSI General Assembly and Scientific Symposium

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During quiet periods of Northward IMF, CLUSTER observed electron acceleration structures at high altitudes along magnetic field lines connected to the polar and extended along the magnetopause boundary layers. The electrons are observed to be successively earthward and outward accelerated, forming current sheets of opposite polarities. The precipitating electrons are accelerated to keV-energies in relatively stable and broad structures. The outflowing electron beams, accelerated to weaker energies (tens of eV), form structures at much smaller scales. These acceleration structures are suggested to result from electrostatic structures generated at the interface between the magnetopause boundary layers and the lobes.

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Monopolar and bipolar auroral electric fields and their effects

Cited by 13 publications

References 32 publications

Wave signatures and electrostatic phenomena above aurora: Cluster observations and modeling

Wave signatures and electrostatic phenomena above aurora: Cluster observations and modeling

Polar cap ion beams during periods of northward IMF: Cluster statistical results

CLUSTER observations of electrostatic acceleration structures above the polar cap and implications for their origin in the magnetopause boundary layer

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