Measurements of field-aligned currents in a multiple auroral arc system

Sesiano, Jean; Cloutier, P. A.

doi:10.1029/ja081i001p00116

Cited by 28 publications

(9 citation statements)

References 18 publications

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“…Rankin et al () used a MHD simulation including kinetic and inertial effects during the evolution of the field line resonances (FLRs), which can induce parallel electric fields and lead to the downward acceleration of electrons. Sesiano and Cloutier () compared their observations with predictions based on the theories of Atkinson () and Sato and Holzer () and found an agreement with several observed parameters, specifically, arc width and spacing, electric field, and current. Another mechanism producing periodic structure is the stationary inertial Alfvén wave, which is generated by plasma drift across FAC sheets Knudsen ().…”

Section: Introductionmentioning

confidence: 68%

Swarm Observation of Field‐Aligned Currents Associated With Multiple Auroral Arc Systems

Knudsen

Gillies

et al. 2017

JGR Space Physics

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Auroral arcs occur in regions of upward field‐aligned currents (FACs); however, the relation is not one to one, since kinetic energy of the current‐carrying electrons is also important in the production of auroral luminosity. Multiple auroral arc systems provide an opportunity to study the relation between FACs and auroral brightness in detail. In this study, we have identified two types of FAC configurations in multiple parallel arc systems using ground‐based optical data from the Time History of Events and Macroscale Interactions during Substorms all‐sky imagers, magnetometers and electric field instruments on board the Swarm satellites. In “unipolar FAC” events, each arc is an intensification within a broad, unipolar current sheet and downward return currents occur outside of this broad sheet. In “multipolar FAC” events, multiple arc systems represent a collection of multiple up/down current pairs. By collecting 17 events with unipolar FAC and 12 events with multipolar FACs, we find that (1) unipolar FAC events occur most frequently between 20 and 21 magnetic local time and multipolar FAC events tend to occur around local midnight and within 1 h after substorm onset. (2) Arcs in unipolar FAC systems have a typical width of 10–20 km and a spacing of 25–50 km. Arcs in multipolar FAC systems are wider and more separated. (3) Upward currents with more arcs embedded have larger intensities and widths. (4) Electric fields are strong and highly structured on the edges of multiple arc system with unipolar FAC. The fact that arcs with unipolar FAC are much more highly structured than the associated currents suggests that arc multiplicity is indicative not of a structured generator deep in the magnetosphere, but rather of the magnetosphere‐ionosphere coupling process.

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Section: Introductionmentioning

confidence: 68%

Swarm Observation of Field‐Aligned Currents Associated With Multiple Auroral Arc Systems

Knudsen

Gillies

et al. 2017

JGR Space Physics

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“…Field-aligned (FA) currents in multiple auroral arcs at the nightside have been measured several times in rocket auroral magnetic field experiments (Casserly and Cloutier, 1975;Sesiano and Cloutier, 1976) while, until recently, they were only noted rarely from satellite magnetometer measurements (see however, Lanchester and Wallis 1985;Bythrow et al, 1986;Potemra et al 1987). In the 90s some prominent cases of multiple current sheets within the auroral oval were reported by Fukunishi et al, (1991); Obara et al, (1993) from AKEBONO satellite, Luhr et al, (1994) and Ohtani et al, (1994) from FREJA satellite.…”

Section: Introductionmentioning

confidence: 87%

Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites

et al. 1997

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Abstract. A case is described of multiple current sheets crossed by the MAGION-2 satellite in the near-midnight quieting auroral oval. The data were obtained by the magnetometer experiment onboard. Results show during a quieting period after a preceding substorm, or during an early growth phase of the next substorm, two double-sheet current bands, POLB and EQUB, located at respectively the polar and equatorial borders of the auroral oval separated by about 500 km in latitude. This is consistent with the double-oval structure during recovery introduced by Elphinstone et al. (1995). Within the POLB, the magnetic field data show simultaneous existence of several narrow parallel bipolar current sheets within the upward current branch (at 69.5-70.3°i nvariant latitude) with an adjacent downward current branch at its polar side at (70.5-71.3°). The EQUB was similarly stratified and located at 61.2-63.5°invariant latitude. The narrow current sheets were separated on average by about 35 km and 15 km, respectively, within the POLB and EQUB. A similar case of double-oval current bands with small-scale structuring of their upward current branches during a quieting period is found in the data from the MAGION-3 satellite. These observations contribute to the double-oval structure of the late recovery phase, and add a small-scale structuring of the upward currents producing the auroral arcs in the double-oval pattern, at least for the cases presented here. Other observations of multiple auroral current sheets and theories of auroral arc multiplicity are briefly discussed. It is suggested that multiple X-lines in the distant tail, and/or leakage of energetic particles and FA currents from a series of plasmoids formed during preceding magnetic activity, could be one cause of highly stratified upward FA currents at the polar edge of the quieting double auroral oval.

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“…The Rice University group has published a number of papers which present in situ useful data capable of testing any theoretical model of quiet auroral arcs [Vondrak et al, 1971;Park and Cloutier, 1971;Cloutier et al, 1973' Anderson andPazich and Anderson, 1975;Spiger and Anderson, 1975;Casserly and Cloutier, 1975;Sesiano and Cloutier, 1976 downward currents do not include auroral (-• 5 keV) electrons, upward currents consist of ambient electrons (<500 eV)and auroral electrons, though the latter contribution is often minor, say, 20%; (4) associated electrojets can either be westward or eastward; (5) arcs usually move equatorward with speeds of the order of 100 m s-X; (6) the field-aligned current intensity is of the order of 10 tzA/m 2, and the electrojet current is of the order of 10 a A; and (7) the arc width is typically 20 km, and the spacing, when it is multiple, is also about the same as the arc width. The underlying physics of the present feedback instability model is described elsewhere [Ogawa and Sato, 1971;Sato and Holzer, 1973].…”

Section: Introductionmentioning

confidence: 99%

A theory of quiet auroral arcs

Sato¹

1978

J. Geophys. Res.

209

222

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Being fed by the large‐scale magnetospheric convection, the coupled ionosphere‐magnetosphere system is subject to a feedback instability for a conjugate perturbation elongating in the east‐west direction, having a width of several tens of kilometers at the ionospheric level, standing along the magnetic field line. The growth time is as short as several minutes even when no hot electrons are involved in the field‐aligned current. Nonlinear development of the feedback instability is numerically investigated, taking hot electrons into account. The following conclusions are obtained. (1) An auroral arc can develop within a few tens of seconds once hot electrons take part. (2) The induced potential associated with the arc can reach several hundred volts. This predicts that the upward field‐aligned current may be provided by electrons with energies of the order of several hundred electron volts, provided anomalous resistivity or double layers develop. (3) The electron density enhancement is directly connected with the upward field‐aligned current and hence the auroral arc. (4) The downward current is localized equatorward of the upward current, when the background electric field is westward. (5) The electrojet current can grow to a few thousand amperes, which can either be westward or eastward, depending on the direction of the electric field. (6) The induced electric field inside the arc is almost constant and different from outside. These results are consistent with the observational results.

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Measurements of field-aligned currents in a multiple auroral arc system

Cited by 28 publications

References 18 publications

Swarm Observation of Field‐Aligned Currents Associated With Multiple Auroral Arc Systems

Swarm Observation of Field‐Aligned Currents Associated With Multiple Auroral Arc Systems

Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites

A theory of quiet auroral arcs

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