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Abstract:
Velocity shears at the boundary layer that forms between a planetary magnetosheath and its magnetosphere can serve as effective voltage generators driving field-aligned currents and powering auroral emissions. Previously, an analytic solution was developed for the field aligned currents and electron precipitation assuming a linear Knight relation as an approximation, which provided a consistent framework to understand the relationship between KH structures measured by THEMIS and auroral bright spots detected by DMSP SSUSI FUV. For more intense shear flow, the linear Knight relation may not be adequate, so to further understand the field-aligned current under these circumstances, we obtain a numerical solution for the field-aligned current and electron precipitation for the velocity shear assuming a nonlinear Knight relation. We compare the nonlinear solution with the linear analytic solution. For small voltages, the nonlinear model exhibits similar behavior to the linear model, verifying the validity of the linear model as an approximation in those cases. However, we find that these two models exhibit different behaviors for sufficiently high voltages, with the nonlinear model current saturating and the current channel broadening. We discuss how the geometry of the driver affects the current channel, and we discuss implications for observations of field-aligned currents.
