SUBSTORM ASSOCIATED RADAR AURORAL SURGES - A STATISTICAL STUDY AND POSSIBLE GENERATION MODEL

Substorm-associated radar auroral surges (SARAS) are a short lived (15 -90 minutes) and spatially localised (similar to 5 degrees of latitude ) perturbation of the plasma convection pattern observed within the au roral E-region. The understanding of such phenomena has important rami fications for the investigation of the larger scale plasma convection and ultimately the coupling of the solar wind, magnetosphere and ionos phere system. A statistical investigation is undertaken of SARAS, obse rved by the Sweden And Britain Radar Experiment (SABRE), in order to p rovide a more extensive examination of the local time occurrence and p ropagation characteristics of the events. The statistical analysis has determined a local time occurrence of observations between 1420 MLT a nd 2200 MLT with a maximum occurrence centred around 1700 MLT. The pro pagation 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 generation mechanism for SARAS based on a proposed model for the production of a similar phenomenon r eferred to as sub-auroral ion drifts (SAIDs). The results of the compa rison suggests that SARAS may result from a similar geophysical mechan ism to that which produces SAID events, but probably occurs at a diffe rent time in the evolution of the event.