Hybrid simulation of magnetotail reconnection

Abstract

Magnetic reconnection is studied by using a large-scale two-dimensional hybrid simulation code that treats the ions fully kinetically and the electrons as a massless fluid. Reconnection is realised by localising an anomalous resistivity in a kinetic tail equilibrium. Within a distance of about 80 lobe ion inertia lengths tailward from the neutral line the fast reconnection jet is characterised over most of the region by partial shell type ion distributions; i.e., the distribution in the central current sheet is not thermalised. Inward drifting cold lobe ions perform in the centre of the reconnection wedge due to the small magnetic field curvature Speiser-type orbits and are subsequently ejected again onto lobe field lines. This situation is similar to the collisionless reconnection scenario described by Hill (1975). The cross-tail current of the thin current sheet is supported by the drifting ions. This current sheet warps and an instability develops further away from the neutral line, resulting in a filamentation of the cross tail current. The simulation demonstrates that ion kinetic effects are of importance for the large-scale structure of the magne-totail during near-Earth reconnection.