Substorm associated radar auroral surges: a statistical study and possible generation model

摘要

Substorm-associated radar auroral surges(SARAS) are a short lived (15–90 minutes) and spatially localised (~5° oflatitude) perturbation of the plasma convection pattern observed within theauroral E-region. The understanding of such phenomena has importantramifications for the investigation of the larger scale plasma convection andultimately the coupling of the solar wind, magnetosphere and ionosphere system.A statistical investigation is undertaken of SARAS, observed by the Sweden AndBritain Radar Experiment (SABRE), in order to provide a more extensiveexamination of the local time occurrence and propagation characteristics of theevents. The statistical analysis has determined a local time occurrence ofobservations between 1420 MLT and 2200 MLT with a maximum occurrence centredaround 1700 MLT. The propagation velocity of the SARAS feature through the SABREfield of view was found to be predominately L-shell aligned with a velocitycentred around 1750 m s–1 and within the range 500 m s–1and 3500 m s–1. This comprehensive examination of the SARAS providesthe opportunity to discuss, qualitatively, a possible generation mechanism forSARAS based on a proposed model for the production of a similar phenomenonreferred to as sub-auroral ion drifts (SAIDs). The results of the comparisonsuggests that SARAS may result from a similar geophysical mechanism to thatwhich produces SAID events, but probably occurs at a different time in theevolution of the event.Key words. Substorms · Auroral surges · Plasmacon-vection · Sub-auroral ion drifts