... Arcs are the most typical auroral forms in the premidnight sector auroral oval . ... There are two types of electric fields related to auroral arcs (see, e.g., Johnson et al., ... The first one, polarization electric field, forms withing the arc because of the increased ionospheric conductivity (de la Beaujardiere, 1977, 1981). ... Res., ... Lanchester, B. S., K. Kaila, I. W. McCrea, Relationship between large horizontal electric fields and auroral arc elements, J. Geophys. ... Geophys., ...