K.: Substorm associated radar auroral surges: a statistical study and a possible generation model, Ann

Abstract. Substorm-associated radar auroral surges (SARAS) are a short lived (15–90 minutes) and spatially localised (5 ° of latitude) perturbation of the plasma convection pattern observed within the auroral E-region. The understanding of such phenomena has important ramifications for the investigation of the larger scale plasma convection and ultimately the coupling of the solar wind, magnetosphere and iono-sphere system. A statistical investigation is undertaken of SARAS, observed by the Sweden And Britain Radar Experiment (SABRE), in order to provide a more extensive examination of the local time occurrence and propagation characteristics of the events. The statistical analysis has determined a local time occurrence of observations between 1420 MLT and 2200 MLT with a maximum occurrence centred around 1700 MLT. The propagation velocity of the SARAS feature through the SABRE field of view was found to be predominately L-shell aligned with a velocity centred around 1750 m s)1 and within the range 500 m s)1 and 3500 m s)1. This comprehensive examination of the SARAS provides the opportunity to discuss, qualitatively, a possible gener-ation mechanism for SARAS based on a proposed model for the production of a similar phenomenon referred to as sub-auroral ion drifts (SAIDs). The results of the comparison suggests that SARAS may result from a similar geophysical mechanism to that which produces SAID events, but probably occurs at a dierent time in the evolution of the event. Key words. Substorms á Auroral surges á Plasma con-vection á Sub-auroral ion drifts