A stable auroral red (SAR) arc with multiple emission features

Abstract

Stable auroral red (SAR) arcs offer subvisible evidence for storm time linkages between the inner magnetosphere and the midlatitude ionosphere. A SAR arc's defining characteristics are horizon-to-horizon east-west extent, a few degrees of latitude in meridional extent, emission only at the oxygen 6300 Å line, and minimal brightness changes during a night—effects readily provided by steady heat conduction from the ring current-plasmapause interaction region. Here we describe a typical SAR arc (brightness ~300 rayleighs) with several superimposed patches of emission in two oxygen lines (with a 6300 Å/5577 Å ratio of ~40). We find no evidence for highly localized heating effects but rather evidence from GPS satellites supporting low-energy electron precipitation as the SAR arc modulating mechanism. Seven brightness peaks with average longitude spacing of ~4° define a new spatial pattern for SAR arc studies.