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Ann. Geophys., 22, 2541-2546, 2004
www.ann-geophys.net/22/2541/2004/
© European Geosciences Union 2004
Double peak structure and diamagnetic wings of the magnetotail current sheet
G. Zimbardo1,*, A. Greco1,*, P. Veltri1,*, A. L. Taktakishvili2, and L. M. Zelenyi3
1Physics Department, University of Calabria, Ponte P. Bucci, Cubo 31C, I-87036 Rende, Italy
2Abastumani Astrophysical Observatory, A. Kazbegi str., 2a, 380060, Tbilisi, Georgia
3Space Research Institute, Profsoyuznaya 84/32, 117810 Moscow, Russia
*Also at Istituto Nazionale di Fisica della Materia, Unita’ di Cosenza, Italy
Abstract. Recent Cluster observations in the magnetotail at about
20 Earth radii downtail have unambiguously shown that sometimes
the current sheet is bifurcated, i.e. it is divided in two
layers. We report numerical simulations of
the ion dynamics in a quasi-neutral sheet in the presence of
magnetic turbulence, which is often observed in the magnetotail, and
for various anisotropies of the ion distribution function.
Ions are injected at the
boundary of the simulation box with a velocity distribution corresponding
to a shifted Maxwellian. The simulation parameters, are adjusted
to be similar to those of Cluster observations.
We find that even for moderate fluctuation levels,
the computed current density profile develops a double peak,
in agreement with the observations. By varying the anisotropy of the
injected distribution function, we are able to reproduce, for weak
anisotropy, the magnetic field overshoots which are sometimes observed
prior to magnetotail traversals. Therefore, we suggest an ion current
profile with a double peak due to magnetic turbulence, and with possible
diamagnetic current wings, present in the case of weak anisotropy
of the ion distribution function.
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