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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 25, issue 11
Ann. Geophys., 25, 2413–2425, 2007
https://doi.org/10.5194/angeo-25-2413-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 25, 2413–2425, 2007
https://doi.org/10.5194/angeo-25-2413-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.

  29 Nov 2007

29 Nov 2007

Scale sizes of intense auroral electric fields observed by Cluster

T. Johansson1, G. Marklund1, T. Karlsson1, S. Liléo1, P.-A. Lindqvist1, H. Nilsson2, and S. Buchert3 T. Johansson et al.
  • 1Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden
  • 2Swedish Institute of Space Physics, Kiruna, Sweden
  • 3Swedish Institute of Space Physics, Uppsala, Sweden

Abstract. The scale sizes of intense (>0.15 V/m, mapped to the ionosphere), high-altitude (4–7 RE geocentric distance) auroral electric fields (measured by the Cluster EFW instrument) have been determined in a statistical study. Monopolar and bipolar electric fields, and converging and diverging events, are separated. The relations between the scale size, the intensity and the potential variation are investigated.

The electric field scale sizes are further compared with the scale sizes and widths of the associated field-aligned currents (FACs). The influence of, or relation between, other parameters (proton gyroradius, plasma density gradients, and geomagnetic activity), and the electric field scale sizes are considered.

The median scale sizes of these auroral electric field structures are found to be similar to the median scale sizes of the associated FACs and the density gradients (all in the range 4.2–4.9 km) but not to the median proton gyroradius or the proton inertial scale length at these times and locations (22–30 km). (The scales are mapped to the ionospheric altitude for reference.)

The electric field scale sizes during summer months and high geomagnetic activity (Kp>3) are typically 2–3 km, smaller than the typical 4–5 km scale sizes during winter months and low geomagnetic activity (Kp≤3), indicating a dependence on ionospheric conductivity.

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