Latitudinal structures of discrete arcs resulting from viscous interaction between sheared plasma flows |
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Institution: | 1. The Aerospace Corporation, El Segundo, CA, United States;2. Department of Physics and Astronomy, Clemson University, Clemson, SC, United States;3. High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, United States;4. UCLA, Los Angeles, CA, United States;5. School of Space and Environment, Beihang University, Beijing, China |
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Abstract: | Latitudinal structures of discrete arcs are modelled as a consequence of the quasi-steady magnetosphere-ionosphere coupling involving viscous interaction between sunward and anti-sunward plasma flows in the magnetosphere. The quasi-steady state in the magnetosphere and ionosphere coupling is described by the magnetospheric and ionospheric current conservation and the field-aligned currentpotential relation assuming adiabatic electron motion along field lines. The upward and downward fieldaligned currents are assumed to be stably maintained by vorticity-induced space charges in the region of plasma flow reversal, where divergence of the magnetospheric electric field E⊥ is negative and positive, respectively. By introducing the effective conductance Σdc arising from the anomalous viscosity, a specific relation between the dc field-aligned current density J∥ and the magnetospheric electric field E⊥ is derived as . Sufficiently large potential drops to accelerate auroral electrons are shown to exist along the auroral field lines originating from the flow reversal region with div . It is shown that the latitudinal structure of a discrete arc is primarily determined by the magnetospheric potential structure and the characteristic width is on the order of 10 km at the ionospheric altitude. |
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