Convection and auroral response to a southward turning of the IMF: Polar UVI, CUTLASS, and IMAGE signatures of transient magnetic flux transfer at the magnetopause

We present the first spacecraft-borne imager observations of the auroral ma nifestation of transient magnetic flux transfer at the magnetopause. During an interval of interplanetary magnetic field B-z approximate to -10 nT, B- y approximate to 10 nT, and solar wind dynamic pressure and velocity P-SW a pproximate to 5 nPa and nu(SW) approximate to 650 km s(-1), Polar Ultraviol et Imager (UVI) images show a sequence of events, each of which begins as a bifurcation of the main auroral oval in the 14 to 16 magnetic local time ( MLT) sector which subsequently progresses antisunward (eastward) at 2 km s( -1) toward the 19 MLT sector. The poleward portion of the bifurcation is in terpreted as a poleward-moving auroral form (PMAF) as has previously been o bserved by ground-based optical instrumentation and identified as the auror al signature of flux transfer events. Ground-based measurements of the asso ciated plasma drift, made with the Cooperative U.K. Twin Located Auroral So unding System (CUTLASS) Finland HF radar, show poleward (1 km s(-1)) and we stward (1 km s(-1)) convection flow, consistent with the B-y tension force, as well as poleward-moving regions of backscatter. International Monitor f or Auroral Geomagnetic Effects (IMAGE) magnetometers within the radar field of view observe poleward-progressing, 10 min period, X component magnetic deflections, which are consistent with the effect of Hall currents associat ed with the plasma flow. The combined radar and optical observations sugges t that the PMAFs can be 3500 km or 7 hours of MLT in length. The antisunwar d motion of the bifurcation of the auroral oval is interpreted as an expans ion of the reconnection X line along the flank of the magnetopause.