Electric fields associated with post-noon auroras

Kozlovsky, A.1, Turunen, T.2, Aikio, A.3, Pitkänen, T.3, Kauristie, K.4 and Massetti, S.5

1 Sodankylä Geophysical Observatory, Oulu unit, Oulu, Finland
2 Sodankylä Geophysical Observatory, Sodankylä, Finland
3 Department of Physical Sciences, University of Oulu, Oulu, Finland
4 Finnish Meteorological Institute, Helsinki, Finland
5 IFSI-INAF, Roma, Italy

In November 2006, a special EISCAT campaign was performed on Svalbard to investigate electric fields associated with the post-noon (12-17 MLT) auroral arcs observed by the all-sky cameras in Longyerbyen and Ny-Alesund. The most important is the northward (perpendicular to auroral arcs) electric field component, which was inferred from the EISCAT Svalbard Radar (ESR) measurements with the radar beam directed to west. The observed auroras are poleward moving auroral forms (PMAF) occurring during different IMF conditions (southward, northward, and near-zero IMF Bz). The auroral arcs and associated electric field patterns are discussed in connection with possible mechanisms for the aurora formation. The discussed mechanisms are the dayside reconnection driven by southward IMF, the interchange instability which likely occurs during northward IMF, and the flow shear created due to magnetospheric eigenmode toroidal oscillations. The electric field (plasma flow) patterns are shown to be important indicator of the arc generation mechanisms.