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Ann. Geophys., 24, 1713-1723, 2006
www.ann-geophys.net/24/1713/2006/
© European Geosciences Union 2006
On the profile of intense high-altitude auroral electric fields at magnetospheric boundaries
T. Johansson1, G. Marklund1, T. Karlsson1, S. Liléo1, P.-A. Lindqvist1, A. Marchaudon2, H. Nilsson3, and A. Fazakerley4
1Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden
2LPCE/CNRS, Orleans Cedex, France
3Swedish Institute of Space Physics, Kiruna, Sweden
4Mullard Space Science Laboratory, University College, London, UK
Abstract. The profile of intense high-altitude electric fields on auroral
field lines has been studied using Cluster data. A total of 41
events with mapped electric field magnitudes in the range between
0.5–1 V/m were examined, 27 of which were co-located with a plasma
boundary, defined by gradients in particle flux, plasma density
and plasma temperature. Monopolar electric field profiles were
observed in 11 and bipolar electric field profiles in 16 of these
boundary-associated electric field events. Of the monopolar
fields, all but one occurred at the polar cap boundary in the late
evening and midnight sectors, and the electric fields were
typically directed equatorward, whereas the bipolar fields all
occurred at plasma boundaries clearly within the plasma sheet.
These results support the prediction by Marklund et al. (2004), that the
electric field profile depends on whether plasma populations, able
to support intense field-aligned currents and closure by Pedersen
currents, exist on both sides, or one side only, of the boundary.
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