Statistical study of the relationship between enhanced polar cap flows and PBIs
Abstract
Poleward boundary intensifications (PBIs) are auroral disturbances along the poleward boundary of the auroral oval and occur during all levels of geomagnetic activity. Using radar and all-sky imager observations, previous case studies have given evidence that longitudinally localized flow bursts in the polar cap that are directed toward the open-closed field line boundary precede PBIs. The present study analyzes a larger number of events and examines if this polar cap flow-PBI relationship is commonly observed. We use coordinated observations of THEMIS all sky imagers and Super Dual Auroral Radar Network (SuperDARN) at Rankin Inlet and mainly focus on isolated PBIs with weak preceding auroral activity and a step-like change of intensity in time. From January to March 2012, we find 19 PBIs satisfying our criteria and 17 of them were preceded by longitudinally narrow, equatorward directed flow bursts within the nightside polar cap having line-of-sight velocity >~150 m/s above the background,. Such flow enhancements were not detected for the other two events, although the flow data indicate weak enhancements >100 m/s. The flow bursts statistically occurred simultaneously with or 1-2 min before the PBI initiations, and the duration of flow bursts was comparable with that of the PBIs. We also find cases when multiple PBIs are preceded by multiple enhanced flows in the polar cap. The remarkably high occurrence of the association between enhanced polar cap flows and PBIs indicates that enhanced meso-scale flows within the open field line that traverse the open-closed field line boundary may be responsible for the formation of PBIs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMSA23B..03Z
- Keywords:
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- 2407 IONOSPHERE / Auroral ionosphere