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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 12
Ann. Geophys., 23, 3685–3698, 2005
https://doi.org/10.5194/angeo-23-3685-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3685–3698, 2005
https://doi.org/10.5194/angeo-23-3685-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Dec 2005

23 Dec 2005

Under and over-adiabatic electrons through a perpendicular collisionless shock: theory versus simulations

P. Savoini1, B. Lembège1, V. Krasnosselskhik2, and Y. Kuramitsu2 P. Savoini et al.
  • 1CETP/UVSQ, 32–40, Avenue de l’Europe, 78140 Vélizy, France
  • 2LPCE/CNRS, 3a, Avenue de la recherche scientifique, 45071 Orléans la Source, France

Abstract. Test particle simulations are performed in order to analyze in detail the dynamics of transmitted electrons through a supercritical, strictly perpendicular, collisionless shock. In addition to adiabatic particles, two distinct nonadiabatic populations are observed surprisingly: (i) first, an over-adiabatic population characterized by an increase in the gyrating velocity higher than that expected from the conservation of the magnetic moment µ, and (ii) second, an under-adiabatic population characterized by a decrease in this velocity. Results show that both nonadiabatic populations have their pitch angle more aligned along the magnetic field than the adiabatic one at the time these hit the shock front. The formation of "under" and "over-adiabatic" particles strongly depends on their local injection conditions through the large amplitude cross-shock potential present within the shock front. A simplified theoretical model validates these results and points out the important role of the electric field as seen by the electrons. A classification shows that both nonadiabatic electrons are issued from the core part of the upstream distributionÊ function. In contrast, suprathermal and tail electrons only contribute to the adiabatic population; nevertheless, the core part of the upstream distribution contributes at a lower percentage to the adiabatic electrons. Under-adiabatic electrons are characterized by small injection angles θinj≤90°, whereas "over-adiabatic" particles have high injection angles θinj>90° (where θinj is the angle between the local gyrating velocity vector and the shock normal).

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