Abstract
Auroral bright spots have been observed at Earth, Jupiter, and Saturn in
regions that map to the boundary layer. It has been suggested that the
bright spots are associated with Kelvin-Helmholtz instability. We
utilize a quasistatic magnetosphere-ionosphere coupling model driven by
a vortex in the boundary layer to determine how the field-aligned
current structure depends on ionospheric and boundary layer parameters.
We compare vortex induced currents with shear-flow induced currents. We
find that the strength of the maximum currents are comparable, but the
structure is significantly different. For a vortex, the current and
electron precipitation maximize when the vortex size mapped to the
ionosphere is approximately 1.5 L, where
L=(Σp/κ)1/2 is the auroral
scale length, Σp is the Pedersen conductivity,
and κ is the Knight parameter. For a vortex, the current width provides
a direct measure of the size, Δ, of the boundary layer structure, while
shear-flow aurora generally are determined by the larger of Δ or
L. For comparison with observations, an event is considered where
auroral bright spots in the ionosphere are detected by DMSP SUSSI UVI
when Kelvin-Helmholtz structures are observed on the dusk flank by
THEMIS.