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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union

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Nonlin. Processes Geophys., 16, 365-372, 2009
https://doi.org/10.5194/npg-16-365-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
30 Apr 2009
On the ionospheric coupling of auroral electric fields
G. T. Marklund Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, KTH 10044 Stockholm, Sweden
Abstract. The quasi-static coupling of high-altitude potential structures and electric fields to the ionosphere is discussed with particular focus on the downward field-aligned current (FAC) region. Results are presented from a preliminary analysis of a selection of electric field events observed by Cluster above the acceleration region. The degree of coupling is here estimated as the ratio between the magnetic field-aligned potential drop, ΔΦII, as inferred from the characteristic energy of upward ion (electron) beams for the upward (downward) current region and the high-altitude perpendicular (to B) potential, ΔΦbot, as calculated by integrating the perpendicular electric field across the structure. For upward currents, the coupling can be expressed analytically, using the linear current-voltage relation, as outlined by Weimer et al. (1985). This gives a scale size dependent coupling where structures are coupled (decoupled) above (below) a critical scale size. For downward currents, the current-voltage relation is highly non-linear which complicates the understanding of how the coupling works. Results from this experimental study indicate that small-scale structures are decoupled, similar to small-scale structures in the upward current region. There are, however, exceptions to this rule as illustrated by Cluster results of small-scale intense electric fields, correlated with downward currents, indicating a perfect coupling between the ionosphere and Cluster altitude.

Citation: Marklund, G. T.: On the ionospheric coupling of auroral electric fields, Nonlin. Processes Geophys., 16, 365-372, https://doi.org/10.5194/npg-16-365-2009, 2009.
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