Global and local processes of thin current sheet formation during substorm growth phase

Formation of thin current sheets in Earth's magnetotail is a critical element of the magnetosphere dynamics. The configuration and stability of these thin current sheets control the onset of magnetic reconnection and particle acceleration in the magnetotail during substorms and other geomagnetic activities. In recent years, multipoint observations, kinetic and hybrid simulations have significantly improved our understanding of the structure and dynamics of thin current sheets, including their ion kinetic physics. Global hybrid simulations have also revealed many details of ion kinetics in thin current sheet physics. In this paper we review current understanding of current sheet physics and discuss our recent observational and simulation results on thin current sheet formation, emphasizing the kinetics of current sheet thinning, multi-component ion populations, the role of electron anisotropy and ion agyrotropy, and the role of the ionosphere.