Auroral streamers and magnetic flux closure

On 7 December 2000 at 2200 UT an auroral streamer was observed to develop above Scandinavia with the IMAGE-FUV global imagers. The ionospheric equivalent current deduced from the MIRACLE-IMAGE Scandinavian ground-based network of magnetometers is typical of a substorm-time streamer. Observations of the proton aurora using the SI12 imager onboard the IMAGE satellite are combined with measurements of the ionospheric convection obtained by the SuperDARN radar network to compute the dayside merging and nightside flux closure rates. On the basis of this and other similar events, it is found that auroral streamers appear during the period of most intense flux closure in the magnetotail, most often shortly after substorm onset. The ionospheric convection velocity, as measured by SuperDARN, appears to be reduced in the vicinity of the streamer, suggesting de-coupling of magnetospheric and ionospheric plasma flows in the region of enhanced ionospheric conductance.