Black & Bright Auroral Vortices - Driven by Mirrored Rolling Magnetic Carpets
Abstract
Abstract Auroral emissions occur mainly when electrons streaming downward along geomagnetic field lines collide with the upper atmosphere at high latitudes, appearing in two types: diffuse and discrete. Diffuse aurora is faint and patchy, resulting from electron wave scattering. Discrete auroras (e.g., arcs, vortices, omega bands, etc.) are due to electron precipitation along geomagnetic field-aligned currents. However, the field-aligned current generation and circuit configuration of auroral vortices remain unknown. Here, we show a mechanism of rolling magnetic carpets, initiated by azimuthal flow shears in the near-tail plasma sheet. We found that a Kelvin-Helmholtz vortex in the inner plasma sheet (6-8 Earth radii) could roll up magnetic fields, like coiling up a carpet (while generating field-aligned currents). It bridges vortices in the ionosphere and those in the magnetotail, producing a black/bright spiraling auroral footprint when it carries field-aligned current into/away from the ionosphere. At the equator, the circuit is initiated and sustained by a generator j∙E0. We have demonstrated that tracing auroral vortices outward can effectively identify field-aligned current generation in remote regions, which can extend to the broader correlation between auroral dynamics and shear flows in the outer magnetosphere.
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