Abstract
The structure of auroral arcs sustained by field line resonances (FLRs) is determined using a model that describes the interplay between ionospheric feedback, nonlinear, and dispersive effects in a curvilinear geomagnetic topology. The model includes modulation of Pedersen conductance by hundreds of eV electrons that precipitate in the ionosphere through the action of shear Alfvén wave field‐aligned currents (FACs). The competition between ionospheric feedback dissipation, wave dispersion, and nonlinearity results in large‐amplitude, long‐period oscillations of the FAC, and in emission of slow‐moving small‐scale secondary auroral arcs and density perturbations. Using observed values of nightside conductivities and realistic topology of geomagnetic field lines, we obtain FLRs with frequencies in the range of a few mHz, spatial scales up to several km near the ionosphere, and FAC amplitudes extending to tens of μA/m2. Our model explains the excitation of structured auroral arcs in regions of low ionospheric conductance.
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