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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 32, issue 6
Ann. Geophys., 32, 643-650, 2014
https://doi.org/10.5194/angeo-32-643-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 32, 643-650, 2014
https://doi.org/10.5194/angeo-32-643-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 13 Jun 2014

Regular paper | 13 Jun 2014

Superdiffusion revisited in view of collisionless reconnection

R. A. Treumann1,2,* and W. Baumjohann3 R. A. Treumann and W. Baumjohann
  • 1Department of Geophysics and Environmental Sciences, Munich University, Munich, Germany
  • 2Department of Physics and Astronomy, Dartmouth College, Hanover NH 03755, USA
  • 3Space Research Institute, Austrian Academy of Sciences, Graz, Austria
  • *currently at: International Space Science Institute, Bern, Switzerland

Abstract. The concept of diffusion in collisionless space plasmas like those near the magnetopause and in the geomagnetic tail during reconnection is reexamined making use of the division of particle orbits into waiting orbits and break-outs into ballistic motion lying at the bottom, for instance, of Lévy flights. The rms average displacement in this case increases with time, describing superdiffusion, though faster than classical, is still a weak process, being however strong enough to support fast reconnection. Referring to two kinds of numerical particle-in-cell simulations we determine the anomalous diffusion coefficient, the anomalous collision frequency on which the diffusion process is based, and construct a relation between the diffusion coefficients and the resistive scale. The anomalous collision frequency from electron pseudo-viscosity in reconnection turns out to be of the order of the lower-hybrid frequency with the latter providing a lower limit, thus making similar assumptions physically meaningful. Tentative though not completely justified use of the κ distribution yields κ ≈ 6 in the reconnection diffusion region and, for the anomalous diffusion coefficient, the order of several times Bohm diffusivity.

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