Small-scale auroral arc distortions

Hallinan, T. J.; Davis, T. N.

doi:10.1016/0032-0633(70)90007-3

Cited by 235 publications

(166 citation statements)

References 12 publications

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“…They showed that without a resistive layer a combination of KH and tearing instabilities lead to vortices similar to folds and the eventual breakup of the planar arc into distorted fine-scale sheets and filamentary currents, while with a resistive layer KH instability dominates leading to the formation of auroral folds. Our observations may fit their prediction as follows: in the first stage, within a thin diffuse arc of a few km width, the flow shear across the arc is typically a few km/s, leading to a small linear KH growth rate of Hallinan and Davis [1970] of about 5 s at maximum. In the second stage, the arc is getting thicker and brighter, the flow shear is getting larger up to 10 km/s with a large linear KH growth rate of 0.5 s at maximum.…”

Section: Discussionsupporting

confidence: 74%

“…The triggering mechanism has been one of the longest-standing unsolved problems in the magnetospheric physics. Highly sensitive TV observations have shown three basic auroral forms, namely spirals, folds, and curls, which differ from each other in their sizes, vorticities, velocities [Hallinan and Davis, 1970]. Auroral spirals are large-scale vortex configurations with typical sizes from tens to hundreds of km.…”

Section: Introductionmentioning

confidence: 99%

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Turbulent microstructures and formation of folds in auroral breakup arc

et al. 2011

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[1] We conducted a ground-based optical measurement pointing at local magnetic zenith with a narrow field of view of 9.3°by 9.3°, using a high-speed electron multiplier charge-coupled device camera at Poker Flat Research Range. We show evidence that auroral folds were periodically formed in a breakup arc and the luminosity is exponentially increased for about 10 s before an auroral breakup onset. The evolution of turbulent microstructures and the formation of folds may be interpreted by the nonlinear evolution of inertial Alfvén wave (IAW) turbulence in the thin current sheet. On the basis of these optical observations, we discuss a possible role of the ionosphere for modulating the triggering process of the onset via the self-organization of the IAW turbulence associated with Kelvin-Helmholtz and tearing instabilities of the thin current sheet.

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Section: Discussionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Turbulent microstructures and formation of folds in auroral breakup arc

et al. 2011

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“…Nonlinear effects, particularly the convective nonlinearity in the perpendicular equation of motion, can be important in creating the complicated structure in the aurora [e.g., Seyler, 1988Seyler, , 1990Chaston et al, 2008]. 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.…”

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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“…An additional characteristic of such a potential distribution is the existence above the acceleration region of a strong convergent perpendicular electric field. The convergent electric field has also been inferred from the Kelvin-Helmholtz vortices (auroral rays) in arcs [Hallinan and Davis, 1970] and from the countervailing drift motions of the auroral rays in adjacent arc elements [Hallinan and Davis, 1970;Carlqvist and Bostrom, 1970]. The convergent field is often measured by satellites operating above the acceleration region (above 1-2 R•) [Mozer et al, 1977].…”

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confidence: 99%

Relation between optical emissions, particles, electric fields, and Alfvén waves in a multiple rayed arc

Hallinan¹,

Kimball²,

Stenbaek‐Nielsen³

et al. 2001

J. Geophys. Res.

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Abstract. Velocities of rays in auroral arcs were used to infer the perpendicular electric fields above the acceleration region. Using rocket measurements of electron energy as a proxy for the high-altitude potential, the high-altitude perpendicular electric fields were calculated and found to be in good agreement with those derived from the ray motions. Additionally, a 0.6 Hz oscillating electric field at high altitude was postulated on the basis of the passing rays. Such a field was also calculated from the electron energy measurements and was found to be closely related to an Alfv6n wave measured on the payload following a delay of 0.8 s. The measured electron energy flux agreed well with the auroral luminosity down to scale sizes of about 10 km. The combination of ground-based imaging and the measured energy flux also allowed a determination of the lower border altitude of the arcs. They were found to be somewhat higher (130 km) than expected on the basis of the electron energy. A tall rayed arc with a lower border height of 170 km was associated with a burst of suprathermal electrons on the poleward edge of the aurora.

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Small-scale auroral arc distortions

Cited by 235 publications

References 12 publications

Turbulent microstructures and formation of folds in auroral breakup arc

Turbulent microstructures and formation of folds in auroral breakup arc

Development of parallel electric fields at the plasma sheet boundary layer

Relation between optical emissions, particles, electric fields, and Alfvén waves in a multiple rayed arc

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