Kinetic thin current sheets: their formation in relation to magnetotail mesoscale turbulent dynamics

Abstract. Dynamics of the magnetotail plasma sheet (PS) features nonlinear structures on two totally different scales. There are very thin current sheets (CS) on kinetic scale of the ion gyroradius. And there are intense plasma flow and magnetic field variations on mesoscales (a few earth radii); those are interpreted as mostly 2-D MHD turbulence. On the other hand, the specific nature of slow large scale magnetotail evolution leads to large differences in the PS properties and those of the lobe plasma. As a result, while fast reconnection bursts in the tail provide quasi-stationary fast mesoscale reconfigurations in the lobes, they cannot however be accompanied by restructuring of CS on the same fast time scale. Violations of force balance in the PS are thus generated. Simulation using a hybrid code and starting with such imbalance, provides an evidence of very thin kinetic CS structures formation, embedded into the much thicker PS. The momentum balance gets locally restored by means of ion acceleration up to the Alfvénic velocity. The process provides an effective mechanism for transformation of magnetic energy accumulated in the magnetotail, into energy of plasma flows. The fast flows may drive turbulence on shorter spatial scales. In their turn, these motions may serve as an origin for new neutral line generation, and reconnection. Application to substorm phenomenology is discussed.