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Ann. Geophys., 22, 125-140, 2004
www.ann-geophys.net/22/125/2004/
© European Geosciences Union 2004
Quantitative modelling of the closure of meso-scale parallel currents in the nightside ionosphere
A. Marchaudon1, J.-C. Cerisier1, O. Amm2, M. Lester3, C. W. Carlson4, and G. K. Parks4
1Centre d’Etude des Environnements Terrestre et Planétaires, 4 avenue de Neptune, 94107 Saint-Maur-des-Fossés Cedex, France
2Geophysical Research Division, Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
3Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
4Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA
Abstract. On 12 January 2000, during a northward IMF period, two successive conjunctions
occur between the CUTLASS SuperDARN radar pair and the two satellites Ørsted and FAST.
This situation is used to describe and model the electrodynamic of a nightside meso-scale arc
associated with a convection shear. Three field-aligned current sheets, one upward and two
downward on both sides, are observed.
Based on the measurements of the parallel currents and either the conductance or the
electric field profile, a model of the ionospheric current closure is developed along each
satellite orbit. This model is one-dimensional, in a first attempt and a two-dimensional model
is tested for the Ørsted case. These models allow one to quantify the balance between electric field
gradients and ionospheric conductance gradients in the closure of the field-aligned currents.
These radar and satellite data are also combined with images from Polar-UVI, allowing for
a description of the time evolution of the arc between the two satellite passes. The arc is very
dynamic, in spite of quiet solar wind conditions. Periodic enhancements of the convection and
of electron precipitation associated with the arc are observed, probably associated with quasi-periodic
injections of particles due to reconnection in the magnetotail. Also, a northward shift
and a reorganisation of the precipitation pattern are observed, together with a southward shift
of the convection shear.
Key words. Ionosphere (auroral ionosphere; electric fields
and currents; particle precipitation) – Magnetospheric
physics (magnetosphere-ionosphere interactions)
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