Plasma Acceleration in the Magnetotail as an Origin of the Electric Field Generation during a Substorm

Field-aligned currents and westward electrojet enhancement are produced by electric field generation in the magnetotail during a substorm. The space measurements during the substorm and laboratory experiments support the model of earthward electric field production in the magnetotail current sheet. The results of numerical MHD simulation are presented. The quasistationary current sheet is created at plasma jet injection in the perpendicular magnetic field. The current sheet becomes unstable after plasma injection is ceased, and the local plasma velocity along the sheet drops to zero. The instability development produces fast current density enhancement and plasma acceleration by j×B/c force. In such conditions the Earthward j×B/nec electric field should appear.