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

Abstract

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 (~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 (< ~1 h magnetic local time (MLT)) and statistically occur within 10 min and ±1 h MLT from the contact. They appear as poleward boundary intensifications in a thick auroral oval or an intensification of the only resolvable arc within a thin oval, and the latter can also exhibit substantial poleward expansion. When radar echoes are available, they corroborate the association of polar cap arcs with localized enhanced antisunward flows. That the observed oval intensifications are major disturbances that only occur after the impingement of polar cap arcs and near the contact longitude suggest that they are triggered by localized fast flows coming from deep in the polar cap.

Aurora in the Polar Cap: A Review

“…They found that as polar cap arcs (a) and (d) show absolute intensity and retain the faint and continuous emission from the nightside auroral oval, and the poleward boundary of the oval is identified and marked as the dashed light blue curve. Radar measurements (0-20 range gates) from SuperDARN at RKN station are also shown (Zou et al 2015) extend equatorward from high latitude, their contact with the nightside auroral poleward boundary is associated with new and substantial intensifications within the oval for 85% of the time. These intensifications statistically occur within 10 min and ±1 h MLT from the contact.…”

“…Recently, Nishimura et al (2013) and Zou et al (2015) studied the polar cap arc-substorm relation from a different perspective, where they examined the timing when polar cap arcs contact the nightside auroral oval and the onset of substorm-like intensifications (see Fig. 23).…”

Scintillation and irregularities from the nightside part of a Sun‐aligned polar cap arc

“…Convection has been observed to be antisunward in the nightside portion of the arc and either sunward [Eriksson et al, 2006] or mixed [Liou et al, 2005] in the dayside portion of the arc. In the vicinity of polar cap arcs, convection is structured, with multiple reversals, flow shears, and flow channels [e.g., Carlson and Cowley, 2005;Eriksson et al, 2006;Zou et al, 2015].…”

Ion temperature intensification in southern convection flow channels during the 1 October 2001 geomagnetic storm recovery phase

“…Recent studies [ Lyons et al , ; Nishimura et al , ; Lyons et al , ; Zou et al , , ] demonstrate with complex data sets how flow channels enter, transit, and exit the polar cap. Adding to these studies, we employ DMSP passes aligned with their respective magnetic meridians.…”