The Electrodynamics of Transient Reconnection: A Multi-Instrument Case Study.
D. NEUDEGG, S. COWLEY, M.LESTER, T. YEOMAN, G. PROVAN, S. MILAN (1), G.HAERENDEL, W. BAUMJOHANN(2), U. AUSTER, K.-H. FORNACON (3), E. GEORGESCU (2,4) and J. SIGWARTH
(1) University of Leicester, UK
(2) Max-Planck Institut für Extraterrestrische Physik, Germany.
(3) Technische Universität von Braunschweig, Braunschweig.
(4) ISS, Bucharest.
(5) University of Iowa, USA
Optical signatures in the polar ionosphere during a period of magnetopause reconnection are compared with ionospheric flows measured in the cusp 'throat' and dusk cell by the SuperDARN HF radars. Regions of peak FUV emission in the 130.4nm and 135.6nm range observed by the POLAR spacecraft VIS Earth Camera consistently lie at the turning point of the flows from the dusk cell poleward into the throat and within the region of high and varied radar spectral-width associated with the cusp/LLBL. The Equator-S spacecraft was near the magnetopause at the time of the ionospheric observations and geomagnetically conjugate with the near-cusp region of ionosphere observed by the radar. Flux transfer events (FTEs), suggestive of bursty reconnection between the IMF and geomagnetic fields, were observed by Equator-S prior to and during the periods of high FUV emission. Enhanced poleward flow velocities in the polar cusp region, that have been statistically associated with FTEs, consistently lie poleward of the enhanced FUV optical feature. The FUV feature is consistent with the position of the largest upward region-1 field-aligned-current (FAC), associated with electron precipitation, on the dusk edge of the merging gap near the join to the adiaroic boundary of the polar cap. The optical feature moves duskward and equatorward during the course of the reconnection sequence, consistent with expansion of the merging line and of the polar cap with newly added open magnetic flux by the FTEs. The DMSP F14 spacecraft passed through the enhanced FUV region and measured a current density of ~6.6A m-2, far greater than the adjacent regions and consistent with values of previous FAC observations.
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