The field-aligned-current system of a sun-aligned arc over Resolute Bay

We report on the first imaging measurements of a field-aligned-current system associated with a sun-aligned arc over Resolute Bay, Canada. The plasma parameters of the dusk-to-dawn drifting arc and surrounding ionosphere are extracted using the volumetric imaging capabilities of the Resolute Bay Incoherent Scatter Radar – North (RISR–N). Multipoint, line-of-sight plasma drift measurements are used to construct an image of the field-aligned-current system of the arc. Overlaid with red-line and green-line optical data, the current system is shown to be consistent with what is expected of an arc; namely, an upward field-aligned-current lies within the optical body of the arc, and the corresponding downward current lies adjacent to the arc. In this event, the signature of the latter is identifiable by a zonally narrow and meridionally extended F-region plasma density trough of significant magnitude situated along the leading edge of the arc. The trough is sustained by a convolution of chemical recombination and current closure in the field-aligned-current system, and maintains its orientation and position on the leading edge of the arc for the duration of its transit through the RISR-N field-of-view.