Incoherent scatter radar and Freja satellite observations of dayside auroral arcs

Abstract

Coordinated incoherent scatter radar and satellite measurements of dayside auroral arcs are presented. Typical auroral arc observations obtained with this method are shown, and compared with the Freja satellite measurements obtained simultaneously. Short-lived sporadic arcs near noon are found to be associated with a magnetosheath plasma apparently having entered through the high latitude cusp. The arcs correspond to meso-scale features in the magnetosheath injection, and are thus likely to be on open field lines. In the 14 MLT region multiple arcs are observed, and these are associated with electron inverted-V structures seen with Freja. The temperature of the source electron population and the presence of weak magnetosheath-like proton fluxes indicate that the source of the current system associated with the arcs is the low-latitude boundary layer. At times, the radar also shows the sporadic appearance of cusp-like precipitation, giving further evidence for the association of the arcs with boundary layer processes. Furthermore, the radar data show that the convection in the vicinity of the 14 MLT arcs is strongest on the border of the precipitation region, where it amounts to a cross-field potential drop of at least 5 kV.