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We investigate an omega-band event that took place above northern Scandinaviaaround 02:00–02:30 UT on 9 March 1999. In our analysis we use ground basedmagnetometer, optical and riometer measurements together with satellite basedoptical images. The optical and riometer data are used to estimate theionospheric Hall and Pedersen conductances, while ionospheric equivalentcurrents are obtained from the magnetometer measurements. These data sets areused as input in a local KRM calculation, which gives the ionosphericpotential electric field as output, thus giving us a complete picture of theionospheric electrodynamic state during the omega-band event. The overall structure of the electric field and field-aligned current (FAC)provided by the local KRM method are in good agreement with previous studies.Also the E×B drift velocity calculated from the localKRM solution is in good qualitative agreement with the plasma velocitymeasured by the Finnish CUTLASS radar, giving further support for the newlocal KRM method. The high-resolution conductance estimates allow us todiscern the detailed structure of the omega-band current system. The highestHall and Pedersen conductances, ~50 and ~25 S, respectively, arefound at the edges of the bright auroral tongue. Inside the tongue,conductances are somewhat smaller, but still significantly higher thantypical background values. The electric field shows a converging patternaround the tongues, and the field strength drops from ~40 mV/m found atoptically dark regions to ~10 mV/m inside the areas of enhancedconductivity. Downward FAC flow in the dark regions, while upward currentsflow inside the auroral tongue. Additionally, sharp conductance gradients atthe edge of an auroral tongue are associated with narrow strips of intenseFACs, so that a strip of downward current flows at the eastern (leading) edgeand a similar strip of upward current is present at the western (trailing)edge. The Joule heating follows the electric field pattern, so that it isdiminished inside the bright auroral tongue

Electrodynamics of an omega-band as deduced from optical and magnetometer data