Auroral arcs: Result of the interaction of a dynamic magnetosphere with the ionosphere

Atkinson, G.

doi:10.1029/ja075i025p04746

Cited by 240 publications

(211 citation statements)

References 18 publications

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“…Such nonlinear motions can be excited by the Kelvin-Helmholtz instability giving rise to auroral curls [Hallinan and Davis, 1970]. Furthermore, ionospheric feedback instability [Atkinson, 1970;Holzer and Sato, 1973;Sato, 1978;Lysak, 1991;Streltsov and Lotko, 2008] can generate small-scale Alfvén waves due to the interaction with the ionosphere. While these processes are likely to operate and contribute to the structure in the aurora, the phase mixing process has the advantage that it is linear, so that it will operate even if the perturbations are not large, and it is also not affected by a low ionospheric conductivity, which is favored for ionospheric feedback.…”

Section: Discussionmentioning

confidence: 99%

Development of parallel electric fields at the plasma sheet boundary layer

Lysak

Song

2011

J. Geophys. Res.

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[1] Many measurements of auroral particles, in particular recent measurements from the FAST satellite, indicate that the auroral electron distribution is often broad in energy and field-aligned in pitch angle. Such electrons are seen in conjunction with strong kinetic Alfvén waves with small perpendicular wavelength, and so the aurora produced by these electrons has been termed the "Alfvénic aurora." The Alfvénic aurora is predominant at the polar cap boundary of the aurora as well as in the auroral arc that brightens during substorm onset. The process of forming parallel electric fields in Alfvén waves has been investigated by means of three-dimensional two-fluid simulations. Waves with small perpendicular wavelengths can be produced by phase mixing when perpendicular gradients are present in the plasma. At lower altitudes, Alfvén waves can interact with the ionospheric Alfvén resonator and phase mix to scales of a few kilometers. At higher altitudes, the electron thermal speed becomes comparable or larger than the Alfvén speed, and parallel electric fields due to the Landau resonance can develop. This has been modeled in the fluid code by an approximation to the plasma dispersion function used in kinetic theory. Phase mixing is most effective when there are strong gradients, such as at the plasma sheet boundary layer. Simulations indicate that these processes can produce parallel electric fields on scales of a few kilometers (in the cold plasma case) to a few tens of kilometers (in the warm plasma case), comparable to the scale sizes of auroral arcs.

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Section: Discussionmentioning

confidence: 99%

Development of parallel electric fields at the plasma sheet boundary layer

Lysak

Song

2011

J. Geophys. Res.

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“…The mechanism of multiple arc generation by Alfven wave resonance in the ionospheric Alfven resonator (IAR) at the altitude range of 1-2 R E was originally suggested by Atkinson (1970) and described in detail by Trakhtengertz and Feldstein, (1984, 1987a and Lysak, (1990Lysak, ( , 1991. It is unlikely to be consistent with the observed spacing because the respective Alfven waves with k ⊥ )1 of more than~8-10 km according to Forget et al, (1991) will not be trapped in the IAR, and these waves will reach the plasma sheet.…”

Section: Sheet Current Stratification Due To Ionospheric Effectsmentioning

confidence: 99%

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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“…Moreover, preliminary investigations show that the plasma sheet energy conversion at Cluster altitudes only responds weakly to variations in the ionization (as estimated by the F10.7 index) at the ionospheric end of the auroral current circuit. Assuming that the ionospheric feedback mechanism [Atkinson, 1970;Sato, 1978;Lysak, 1991] affects the M-I coupling, auroral acceleration should be more efficient when the ionospheric conductivity is low. If there were a strong correlation between auroral activity and the observed ECRs, the plasma sheet energy conversion at Cluster altitudes would also vary substantially with the ionospheric ionization.…”

Section: Explicit Relation To Auroral Activitymentioning

confidence: 99%

Energy conversion regions as observed by Cluster in the plasma sheet

et al. 2011

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[1] In this article we present a review of recent studies of observations of localized energy conversion regions (ECRs) observed by Cluster in the plasma sheet at altitudes of 15-20R E . By examining variations in the power density, E · J, where E is the electric field and J is the current density, we show that the plasma sheet exhibits a high level of fine structure. Approximately three times as many concentrated load regions (CLRs) (E · J > 0) as concentrated generator regions (CGRs) (E · J < 0) are identified, confirming the average load character of the plasma sheet. Some ECRs are found to relate to auroral activity. While ECRs are relevant for the energy conversion between the electromagnetic field and the particles, bursty bulk flows (BBFs) play a central role for the energy transfer in the plasma sheet. We show that ECRs and BBFs are likely to be related, although details of this relationship are yet to be explored. The plasma sheet energy conversion increases rather simultaneously with increasing geomagnetic activity in both CLRs and CGRs. Consistent with large-scale magnetotail simulations, most of the observed ECRs appear to be rather stationary in space but varying in time. We estimate that the ECR lifetime and scale size are a few minutes and a few R E , respectively. It is conceivable that ECRs rise and vanish locally in significant regions of the plasma sheet, possibly oscillating between load and generator character, while some energy is transmitted as Poynting flux to the ionosphere.

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Auroral arcs: Result of the interaction of a dynamic magnetosphere with the ionosphere

Cited by 240 publications

References 18 publications

Development of parallel electric fields at the plasma sheet boundary layer

Development of parallel electric fields at the plasma sheet boundary layer

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

Energy conversion regions as observed by Cluster in the plasma sheet

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