Articles | Volume 31, issue 7
Ann. Geophys., 31, 1227–1240, 2013
Ann. Geophys., 31, 1227–1240, 2013

Regular paper 18 Jul 2013

Regular paper | 18 Jul 2013

Vlasov simulations of parallel potential drops

H. Gunell1, J. De Keyser1, E. Gamby1, and I. Mann2,3 H. Gunell et al.
  • 1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium
  • 2EISCAT Scientific Association, P.O. Box 812, 981 28 Kiruna, Sweden
  • 3Department of Physics, Umeå University, 901 87 Umeå, Sweden

Abstract. An auroral flux tube is modelled from the magnetospheric equator to the ionosphere using Vlasov simulations. Starting from an initial state, the evolution of the plasma on the flux tube is followed in time. It is found that when applying a voltage between the ends of the flux tube, about two thirds of the potential drop is concentrated in a thin double layer at approximately one Earth radius altitude. The remaining part is situated in an extended region 1–2 Earth radii above the double layer. Waves on the ion timescale develop above the double layer, and they move toward higher altitude at approximately the ion acoustic speed. These waves are seen both in the electric field and as perturbations of the ion and electron distributions, indicative of an instability. Electrons of magnetospheric origin become trapped between the magnetic mirror and the double layer during its formation. At low altitude, waves on electron timescales appear and are seen to be non-uniformly distributed in space. The temporal evolution of the potential profile and the total voltage affect the double layer altitude, which decreases with an increasing field aligned potential drop. A current–voltage relationship is found by running several simulations with different voltages over the system, and it agrees with the Knight relation reasonably well.