Coordinated optical and radar observations of enhanced electric fields within auroral arcs

Safargaleev, V.1, Sergienko, T.2, Kozlovsky, A.3, Sandahl, I.2, Osipenko, S.1 and Brändström, U.2

1 Polar Geophysical Institute, Apatity, Russia
2 Swedish Institute of Space Physics, Kiruna, Sweden
3 Sodankylä Geophysical Observatory, Oulu unit, Oulu, Finland

The first theoretical models of the auroral arc were based mainly on optical observations. The further progress was connected with radar measurements, which confirmed, in particular, the theoretical prediction that the arc itself is a region of enhanced conductivity. For this reason, the electric field within the arc should be smaller than outside. But there were some events reported where the electric field inside the arc increased and as appeared to be correlated with the conductivity (de la Beaujardiére at al., 1981). Although a theoretical interpretation was suggested (Marklund, 1984), the observations were questioned by Lanchester et al. (1996). After that no clear cases of the “correlating arcs” were reported and the field decrease is regarded now as the only possibility for the change of the electric field within the arc. Our paper is a case study of coordinated EISCAT and ALIS observations of a series of auroral arcs. The vector of the ionospheric electric field was inferred from tristatic measurements. The observations showed that the electric field was enhanced every time when the arc crossed the EISCAT beam. Due to high temporal and spatial resolution, the discussed observations do not suffer from disadvantages indicated by Lanchester and verify the presence of “correlating arcs”. A possible interpretation of the observations is suggested.