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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 33, issue 3
Ann. Geophys., 33, 257–266, 2015
https://doi.org/10.5194/angeo-33-257-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 33, 257–266, 2015
https://doi.org/10.5194/angeo-33-257-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 03 Mar 2015

Regular paper | 03 Mar 2015

Magnetic field-aligned plasma currents in gravitational fields

O. E. Garcia1, E. Leer2, H. L. Pécseli3, and J. K. Trulsen2 O. E. Garcia et al.
  • 1Department of Physics and Technology, UiT – The Arctic University of Norway, 9037 Tromsø, Norway
  • 2Department of Theoretical Astrophysics, University of Oslo, 0315 Oslo, Norway
  • 3Department of Physics, University of Oslo, 0316 Oslo, Norway

Abstract. Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. General solutions have to be non-stationary, varying on time scales of many periods of a plasma equivalent to the Brunt–Väisälä frequency. Except for very special choices of parameters, a steady-state solution exists only in an average sense. The conditions at large altitudes turn out to be extremely sensitive to even small changes in parameters at low altitudes. Low frequency fluctuations detected at large altitudes in the polar regions need not be caused by local low frequency instabilities, but merely reflect small fluctuations in conditions at low altitudes.

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Currents due to slow bulk electron motion along vertical magnetic fields are studied for plasmas subject to a gravitational force. A general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. The alternative is that only time-varying solutions exist.
Currents due to slow bulk electron motion along vertical magnetic fields are studied for plasmas...
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