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Ann. Geophys., 18, 1128-1144, 2000
www.ann-geophys.net/18/1128/2000/
© European Geosciences Union 2000
Nonlinear model of short-scale electrodynamics in the auroral ionosphere
J.-M. A. Noël1, J.-P. St.-Maurice1, and P.-L. Blelly2
1Department of Physics and Astronomy, The University of Western-Ontario, London, Ontario, Canada
2Centre d'étude spatiale des rayonnements, Toulouse, France
Abstract. The optical detection of auroral subarcs a
few tens of m wide as well as the direct observation of shears several m/s per m
over km to sub km scales by rocket instrumentation both indicate that violent
and highly localized electrodynamics can occur at times in the auroral
ionosphere over scales 100 m or less in width. These observations as well as the
detection of unstable ion-acoustic waves observed by incoherent radars along the
geomagnetic field lines has motivated us to develop a detailed time-dependent
two-dimensional model of short-scale auroral electrodynamics that uses current
continuity, Ohm's law, and 8-moment transport equations for the ions and
electrons in the presence of large ambient electric fields to describe wide
auroral arcs with sharp edges in response to sharp cut-offs in precipitation
(even though it may be possible to describe thin arcs and ultra-thin arcs with
our model, we have left such a study for future work). We present the essential
elements of this new model and illustrate the model's usefulness with a sample
run for which the ambient electric field is 100 mV/m away from the arc and for
which electron precipitation cuts off over a region 100 m wide. The sample run
demonstrates that parallel current densities of the order of several hundred µA
m-2 can be triggered in these circumstances, together with shears
several m/s per m in magnitude and parallel electric fields of the order of 0.1
mV/m around 130 km altitude. It also illustrates that the local ionospheric
properties like densities, temperature and composition can strongly be affected
by the violent localized electrodynamics and vice-versa.
Key words: Ionosphere (auroral ionosphere, electric
fields and currents, ionosphere-magnetosphere interactions)
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