Distribution of auroral arcs during quiet geomagnetic conditions

Abstract

Auroral arcs observed from the Greenland all‐sky camera network during quiet intervals ( AE <50 nT) have been ordered in corrected geomagnetic latitude/time mass plots for different values of AE . The arcs are distributed in a pattern which is shown to coincide with the precipitation belt of auroral electrons determined by the DMSP satellites. This belt is known to be composed of two parts: an equatorial part (average energy of >500 eV) and a poleward, low‐energy part. Previous studies have shown that the arc pattern is composed of two subpatterns, too, the “polar cap arc pattern” and the “oval arc pattern.” It is demonstrated that the “polar cap arc pattern” is situated in the poleward, low‐energy part of the precipitation belt, connected to the low‐latitude boundary layer, whereas the “oval arc pattern” is in the equatorial higher energy belt, connected to the plasma sheet. The dividing line between the two arc patterns is associated with the boundary of trapped ≥40‐keV electrons. The designation “polar cap arc pattern” is shown to be ambiguous, wherefore it is proposed to replace it by the term “high‐latitude arc pattern.”