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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 1
Ann. Geophys., 27, 381–394, 2009
https://doi.org/10.5194/angeo-27-381-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 381–394, 2009
https://doi.org/10.5194/angeo-27-381-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Jan 2009

23 Jan 2009

Velocity shear and current driven instability in a collisional F-region

P. J. G. Perron1, J.-M. A. Noël1, and J.-P. St.-Maurice2 P. J. G. Perron et al.
  • 1Department of Physics, Royal Military College of Canada, Kingston, Ontario, Canada
  • 2Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Abstract. We have studied how the presence of collisions affects the behavior of instabilities triggered by a combination of shears and parallel currents in the ionosphere under a variety of ion to electron temperature ratios. To this goal we have numerically solved a kinetic dispersion relation, using a relaxation model to describe the effects of ion and electron collisions. We have compared our solutions to expressions derived in a fluid limit which applied only to large electron to ion temperature ratios. We have limited our study to threshold conditions for the current density and the shears. We have studied how the threshold varies as a function of the wave-vector angle direction and as a function of frequency. As expected, we have found that for low frequencies and/or elevated ion to electron temperature ratios, the kinetic dispersion relation has to be used to evaluate the threshold conditions. We have also found that ion velocity shears can significantly lower the field-aligned threshold current needed to trigger the instability, especially for wave-vectors close to the perpendicular to the magnetic field. However the current density and shear requirements remain significantly higher than if collisions are neglected. Therefore, for ionospheric F-region applications, the effect of collisions should be included in the calculation of instabilities associated with horizontal shears in the vertical flow. Furthermore, in many situations of interest the kinetic solutions should be used instead of the fluid limit, in spite of the fact that the latter can be shown to produce qualitatively valid solutions.

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