Joule dissipation in the vicinity of fine auroral structure

Kilometer-scale variability in the high latitude electric field is not mapped from the magnetosphere, but is rather a consequence of structure in the conductance field caused by auroral precipitation. Using a combination of space-based and ground-based measurements, the magnitude of conductance gradients produced by various classes of auroral fine structure is quantified and the influence of these gradients on the dissipation of electromagnetic energy in the ionosphere is evaluated. Auroral forms of <100m width with kinetic energy flux exceeding 20mW/m^2 have been observed to be stationary for >1s. For these time scales the E-region plasma is in approximate chemical equilibrium, and gradient scale lengths of order the electron skin depth (∼60m) can be readily produced. In the presence of a large-scale background current system, such gradients will either lead to intense localized polarization electric fields---and, hence, fine structure in the Joule dissipation rate---or intense localized field-aligned currents. Classes of auroral fine structure are presented that are consistent with each scenario.