Electric fields and currents associated with active aurora

The presence of active aurorae (i.e., auroral break-ups, westward travelling surges and omega bands) in the nighttime auroral oval and the associated spatially confined highly conducting regions severely alter and distort the current flow of the large scale convection-driven electrojet system. Modelling of the current flow within and near to active aurorae based on simultaneous two-dimensional observations of optical aurora, ionospheric electric fields, and magnetic fields on the ground revealed among others three important features: Strong conductivity gradients at the boundaries of break-up aurorae and westward travelling surges lead to the generation of polarization electric fields and enhanced westward current flow. The strong westward current within break-up aurora and behind the surge is at the western edge continued upward along the magnetic field lines by a strong and localized line-type field-aligned current. Omega bands are associated with eastwest orientated pairs of up- and downward directed field-aligned currents and drift eastward with ExB velocity under the influence of the southward directed convection electric field.