Abstract
Abstract. We consider sheared flows in magnetospheric boundary layers of tangential discontinuity type, forming a structure that is embedded in a large-scale convergent perpendicular electric field. We construct a kinetic model that couples the magnetospheric structure with the topside ionosphere. The contribution of magnetospheric electrons and ionospheric electrons and ions is taken into account into the current-voltage relationship derived for an electric potential monotonically decreasing with the altitude. The solution of the current continuity equation gives the distribution of the ionospheric potential consistent with the given magnetospheric electric potential. The model shows that a sheared magnetospheric flow generates current sheets corresponding to upward field-aligned currents, field-aligned potential drops and narrow bands of precipitating energy, as in discrete auroral arcs. Higher velocity magnetospheric sheared flows have the tendency to produce brighter and slightly broader arcs. An increase in arc luminosity is also associated with enhancements of magnetospheric plasma density, in which case the structures are narrower. Finally, the model predicts that an increase of the electron temperature of the magnetospheric flowing plasma corresponds to slightly wider arcs but does not modify their luminosity.
Highlights
Auroras reflect complex phenomena linking the solar wind, the magnetosphere and the upper atmosphere
They argued that such tangential discontinuity (TD) can play the role of generator for discrete auroral arcs, but did not investigate the effects of sheared flows. (II) The Plasma Sheet and its boundary layers as well as the magnetotail are sites where high speed plasma flows and bursty bulk flows were observed on a wide range of locations (e.g. Baumjohann et al, 1990; Angelopoulos et al.,1992; Cao et al.,2006)
The potential distribution obtained from the TD model for various Low Latitude Boundary Layer (LLBL) velocities has been introduced into the expressions (4–7) such that the total field-aligned density can be expressed from Eq (8) as a function of m and i; j|| is introduced into the current continuity equation (1)
Summary
Auroras reflect complex phenomena linking the solar wind, the magnetosphere and the upper atmosphere. In this study we consider that the magnetospheric plasma bulk velocity has a gradient, or shear, in the direction perpendicular to a plasma interface of tangential discontinuity (TD) type, i.e., in a direction perpendicular to the magnetic field. Lundin and Evans (1985) made correlations between satellite observations of plasma structures injected in the LLBL and the occurrence of high latitude, early afternoon, discrete auroral arcs. Kinetic point of view that the tangential discontinuities (TD) formed at the interface between plasmas with different temperatures and/or densities can be the site of an electromotive force They argued that such TDs can play the role of generator for discrete auroral arcs, but did not investigate the effects of sheared flows.
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