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The perturbed neutral circulation in the vicinity of a symmetric stable auroral arc

The neutral response to changes in the energy source associated with the appearance of a symmetric stable auroral arc is simulated using a sophisticated two-dimensional numerical model. The model is a time-dependent one which describes nonlinear, nonhydrostatic viscous flow in a rotating atmosphere. The energy sources are the ion drag momentum source and the Joule and particle precipitation heating sources. The arc model is an idealization of rocket observations of a fairly wide intense arc. The distribution of ion production and electric potential were assumed to be symmetric about the center of the arc and constant along the arc. A significant feature of the forcing is the reduction and reversal of the electric field within the arc. The arc is embedded in a region of enhanced ionization associated with a diffuse aurora. The simulation was carried out for an interval of 1 hour after the onset of the changed forcing. The main findings of our study are as follows: (1) the zonal ion drag force drives strong (∼200 m s−1) counterstreaming zonal winds on opposite sides of the arc; (2) the zonal flow within the arc is accelerated to ∼40% of the electric field drift velocity in the region of high Pedersen conductivity; (3) the nonhydrostatic interplay of buoyancy and vertical pressure gradient forces sets up a large-scale buoyancylike oscillation; (4) the adiabatic circulation driven by the meridional ion drag force contributes to a net cooling in the lower region of the arc during the first half of the simulation; (5) forced convection within the arc resembles convection due to particle heating alone, but particle heating contributed only ∼25% of the net warming; and (6) the lateral extent of the meridional circulation is much more extensive than the lateral extent of the arc and the diffuse aurora.