A mathematical model of the structure and evolution of small‐scale discrete auroral arcs

Seyler, C. E.

doi:10.1029/ja095ia10p17199

Cited by 120 publications

(135 citation statements)

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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].…”

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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“…However, no consistent theoretical treatment of this scenario has yet been presented. Another possibility of creating filamentary structures is instabilities, such as tearing instabilities, in thin current layers between incoming and reflected waves [Seyler, 1990].…”

Section: Alfvénic Arcs/onset Arcsmentioning

confidence: 99%

Six auroral generators: A review

Haerendel

2011

J. Geophys. Res.

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[1] The paper reviews generator processes and configurations of six types of auroral arcs: embedded arcs, Alfvénic arcs, onset arcs, poleward arcs during substorms, auroral streamers, and auroral spirals. The arcs and generators are elements in global current systems, which are classified as Types I and II after Boström. The arcs may be dominated by transient processes or be quasi-stationary. The main emphasis of the paper is on the generator forces. They are pressure gradient forces, magnetic normal or shear stresses, or inertial forces. For three cases, the arcs embedded in the oval convection, the poleward arc during substorms, and the auroral streamers, simple expressions are presented of the currents injected into the ionosphere by the generator process, allowing quantitative evaluations. The relations leading from these currents to other key auroral quantities are summarized. The apparent conflict between the widths of Alfvénic arcs and the transverse scales required for energy coupling to the topside ionospheric plasma is solved by assuming current and field filamentation by multiple reflections in the ionospheric Alfvén resonator. The substorm generator is described as a high-beta plasma layer arising from collapse of the tail current sheet. An essential element in this process is the shedding of excess flux tube entropy through energy dumping in the auroral acceleration process and ionospheric dissipation. The dynamics of this process needs further investigation. The physics of the connection between flow bursts in the tail plasma sheet and the flows associated with auroral streamers in the ionosphere is discussed. Regular auroral spirals and the westward traveling surge have in common a concentration of upward field-aligned current which demands strongly enhanced dissipation. They differ by the processes creating the upward current concentration.

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“…This was determined by solving the linear initial value code. We do not consider the two-dimensional single-tearing mode, as that has been studied before [Seyler, 1988[Seyler, , 1990 whereas AS tend to have A/Lñ -• 1. An important issue in this regard is the ionospheric conductivity.…”

Section: Local Interchange Modementioning

confidence: 99%