Magnetic flux transfer in the 5 April 2010 Galaxy 15 substorm: an unprecedented observation

Abstract. At approximately 08:25 UT on 5 April 2010, a CME-driven shock compressed Earth's magnetosphere and applied about 15 nT of southward IMF for nearly an hour. A substorm growth phase and localized dipolarization at 08:47 UT were followed by large dipolarizations at 09:03 UT and 09:08 UT, observed by GOES West (11) in the midnight sector, and by three THEMIS spacecraft near X =−11, Y =−2 R E . A large electric field at the THEMIS spacecraft indicates so much flux transfer to the inner magnetosphere that "overdipolarization" took place at GOES 11. This transfer is consistent with the ground and space magnetic signature of the substorm current wedge. Significant particle injections were also observed. The ensemble of extreme geophysical conditions, never previously observed, is consistent with the Near-Earth Neutral Line interpretation of substorms, and subjected the Galaxy 15 geosynchronous satellite to space weather conditions which appear to have induced a major operational anomaly.