Polar cap precursor of nightside auroral oval intensifications using polar cap arcs

摘要

Recent radar and optical observations suggested that localized fast flows in the polar cap precede disturbances within the nightside auroral oval. However, how commonly this connection occurs has been difficult to examine due to limited coverage of radar flow measurements and diffuse and dim nature of airglow patches. Polar cap arcs are also associated with fast flows in the polar cap and appear much brighter than patches, allowing evaluation of the interaction between polar cap structures and nightside aurora more definitively. We have surveyed data during six winter seasons and selected quasi-steady polar cap arcs lasting >1 h. Thirty-four arcs are found, and for the majority (similar to 85) of them, as they extend equatorward from high latitude, their contact with the nightside auroral poleward boundary is associated with new and substantial intensifications within the oval. These intensifications are localized (