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Ann. Geophys., 19, 179-188, 2001
www.ann-geophys.net/19/179/2001/
© European Geosciences Union 2001
The UV aurora and ionospheric flows during flux transfer events
Neudegg1,*, Cowley1, McWilliams1, Lester1, Yeoman1, Sigwarth2, Haerendel3, Baumjohann3, Auster4, Fornacon4, and Georgescu5
1Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
2Department of Physics, University of Iowa, USA
3Max-Planck Institut für Extraterrestrische Physik, Garching, Germany
4Technische Universität von Braunschweig, Braunschweig, Germany
5Institute of Space Science, Bucharest, Romania
*Now at: Rutherford-Appleton Laboratory, Oxfordshire OX11 0QX, UK
Correspondence to: T. K. Yeoman, (tim.yeoman@ion.le.ac.uk)
Abstract. Far Ultra Violet (FUV)
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 CUTLASS Hankasalmi HF radar. Regions of peak FUV emission in the
130.4 nm and 135.6 nm range, observed by the Polar spacecraft’s VIS
Earth Camera, consistently lie at the turning point of the flows from the dusk
cell, poleward into the throat, and at the equatorward edge of the region of
high and varied radar spectral-width associated with the cusp. The Equator-S
spacecraft was near the magnetopause at the time of the ionospheric observations
and geomagnetically conjugate with the 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 ionospheric flow velocities
in the polar cusp region, previously shown to be associated with bursty
reconnection, consistently lie poleward of the enhanced FUV optical feature. The
enhanced optical feature is consistent with the expected position of the largest
upward region 1 field-aligned current, associated with electron precipitation,
on the dusk edge of the merging gap. The optical feature moves duskward and
equatorward during the course of the reconnection sequence, consistent with
expansion of the merging line and the polar cap with newly added open magnetic
flux by the FTEs. The DMSP F14 spacecraft passed through the enhanced FUV region
and measured strong, structured electron precipitation far greater than in the
adjacent regions.
Key words. Magnetospheric physics (current systems;
magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions)
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