Simultaneous observations of Sun‐aligned polar cap arcs in both hemispheres by Exos‐C and Viking

On September 25, 1986, the EXOS‐C satellite traversed an intense electron precipitation in the southern polar cap, while the Viking satellite simultaneously obtained image data of the polar cap arc in the northern hemisphere. The energy spectrum of the precipitation, measured by instrumentation aboard EXOS‐C, was very similar to that of adjacent (typical) auroral arcs, and the precipitation in the southern polar cap was observed in the same local time sector in which the arc was found in the northern polar cap. Observations seem to support the view that the polar cap arc occurs on closed field lines and is conjugate in both hemispheres.