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Structure and dynamics of a new class of thin current sheets

Structure and dynamics of a new class of thin current sheets

Publication date: 13 August 2006

Authors: Sitnov, M.I. et al.

Journal: Journal of Geophysical Research
Volume: 111
Issue: A8
Page: 204
Year: 2006

Copyright: American Geophysical Union

New results on a steady state Vlasov theory of current sheets, which generalizes the Harris (1962) model by assuming anisotropic and nongyrotropic plasmas and using the invariant of particle motion in regions of strong gradients, are presented with the aim to explain multiprobe observations of thin current sheets in the geomagnetotail and laboratory experiments, including the effects of current sheet embedding and bifurcation. The dynamics of these sheets is explored using a full particle code with more realistic mass ratio and anisotropy parameters than those used in our earlier works. The results relevant to 2001 CLUSTER observations, with the sheet thickness appreciably exceeding the thermal ion gyroradius, include ion distributions and pressure tensor components, which reveal the important role of nongyrotropic effects on the structure of these sheets. Their flapping motions are distinguished by north-south asymmetry of current profiles, quasi-rectangular shape of the flapping waves, and their small propagation speed, suggesting an explanation of their propagation toward the flanks of the tail sheet. The main effect of the ion anisotropy on the sheets with thickness less than the thermal ion gyroradius, relevant to 2003 CLUSTER observations and laboratory experiments, is their charging, which may limit their minimum thickness, while their structure can be modified by electron anisotropy. Other distinctive features of these sheets are three-peaked current density profiles, found both in simulations and in the steady state theory, the north-south asymmetry of flapping sheets, and the shape of flapping waves, which is drastically different from the case of thicker sheets.

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