On the base of numerical simulation the evolution of current sheet (CS) in the Earth’s magnetotail during geomagnetic perturbations is investigated. The evolution of the pressure tensor in the process of CS thinning to extremely thin configuration playing a key role in large-scale geomagnetic perturbations is considered. It is shown in a frame of numerical experiment that at an early stage the CS is formed with thickness about 8-10 Larmor proton radii and gyrotropic pressure distribution. This stage is characterized by plasma drift motion to CS center and to the Earth, and can be well described by the Chew-Goldberger-Low approximation. At the later stage the extremely thin current sheet is formed in which plasma pressure tensor becomes anisotropic. Estimates of characteristic timescales of the system evolution are made and the agreement with the available experimental data is shown.
$^1$Skobeltsyn Institute of Nuclear Physics, M.V.Lomonosov Moscow State University.\
$^2$Space Research Institute RAS
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