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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

2000; American Geophysical Union; Volume: 105; Issue: A7 Linguagem: Inglês

10.1029/2000ja900022

2156-2202

S. E. Milan, M. Lester, S. W. H. Cowley, M. Brittnacher,

Geomagnetism and Paleomagnetism Studies

We present the first spacecraft‐borne imager observations of the auroral manifestation of transient magnetic flux transfer at the magnetopause. During an interval of interplanetary magnetic field B z ≈ −10 nT, B y ≈ 10 nT, and solar wind dynamic pressure and velocity P sw ≈ 5 nPa and v sw ≈ 650 km s −1 , Polar Ultraviolet 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 interpreted as a poleward‐moving auroral form (PMAF) as has previously been observed by ground‐based optical instrumentation and identified as the auroral signature of flux transfer events. Ground‐based measurements of the associated plasma drift, made with the Cooperative U.K. Twin Located Auroral Sounding System (CUTLASS) Finland HF radar, show poleward (1 km s −1 ) and westward (1 km s −1 ) convection flow, consistent with the B y tension force, as well as poleward‐moving regions of backscatter. International Monitor for 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 associated with the plasma flow. The combined radar and optical observations suggest that the PMAFs can be 3500 km or 7 hours of MLT in length. The antisunward motion of the bifurcation of the auroral oval is interpreted as an expansion of the reconnection X line along the flank of the magnetopause.