Study of current intensification by compression in the Earth magnetotail

Abstract

Current sheet formation and intensification can be studied by compressing an initially uniform or weakly stratified plasma. Recently, the community has been challenged to conduct a common test, the so-called Newton challenge, where a current sheet is slowly compressed by a localized boundary push, eventually leading to magnetic reconnection in the sheet. We revisit the effect of a compression in a kinetic framework, considering also stronger and more sudden pushes leading to shock compression. We consider specifically the additional physics brought about by a full kinetic model. The primary conclusion is that two competing effects are present during compression. First, the heating due to shock compression is not isotropic and tends instead to create strongly anisotropic and nongyrotropic distributions responsible for bifurcating the current channel. Second, current-aligned instabilities, developing in the dawn-dusk direction (often neglected in previous compression studies) create small-scale ripples on the shock front, leading to a more isotropic heating and creating a nonmonotonic final current profile with a centrally peaked structure but with significant side currents at the edges. Copyright 2007 by the American Geophysical Union.