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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 10
Ann. Geophys., 23, 3277–3288, 2005
https://doi.org/10.5194/angeo-23-3277-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3277–3288, 2005
https://doi.org/10.5194/angeo-23-3277-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Nov 2005

30 Nov 2005

Quiet-time mid-latitude trough: influence of convection, field-aligned currents and proton precipitation

H. Nilsson1, T. I. Sergienko1, Y. Ebihara2, and M. Yamauchi1 H. Nilsson et al.
  • 1Swedish Institute of Space Physics, Kiruna, Sweden
  • 2National Institute of Polar Research, Tokyo, Japan

Abstract. A combination of EISCAT CP-3 (latitude scans) and satellite (DMSP) data have been used to study the structure of the quiet-time evening-sector auroral and subauroral ionosphere, in particular the mid-latitude trough. The main mechanism behind trough formation in the quiet-time evening sector ionosphere is believed to be flow stagnation in a region where convection and corotation counteract each other. However, there is also the possibility that field-aligned currents (FAC) more directly modify the ionospheric density if the current is carried by thermal ionospheric electrons. A quantitative test of the flow-stagnation scenario and an estimate of the possible direct effects caused by field-aligned currents have been performed. We found that the electron densities observed can indeed be explained by the flow-stagnation scenario, but the electron density altitude profiles in the trough sometimes differ from what should be expected from flow stagnation. The effect of a downward field-aligned current cannot be identified in the data, but a simple estimate shows that it can affect the ionospheric plasma density, causing decreased ionospheric densities. In the quiet-time region 2 current/trough region there is typically a significant ion production resulting from proton precipitation which may counteract this effect. Charge exchange of the precipitating protons causes a lateral spread and a smooth associated conductance enhancement. Thus, whereas the proton number flux is insufficient to directly carry the evening sector region 2 current, the precipitation in practice produces the necessary charge carriers. We suggest that precipitating protons do play a crucial role in the electrodynamics of the dark evening sector ionosphere by causing a small but smooth conductance enhancement and producing the charge carriers necessary to carry the trough-associated downward field-aligned current.

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