Flapping motions of the magnetotail current sheet excited by nonadiabatic ions

Observations by the Cluster spacecraft on 3 August 2004 are presented as an example of flapping motions of the magnetotail current sheet excited by nonadiabatic ions. It is found that the current sheet up-down motions are exactly corresponding to alternating hemispherical asymmetries of the bouncing ion population. We show that those hemisphere-asymmetric nonadiabatic ion populations are present in the magnetic field configuration with an effective finite guiding component due to the local current sheet inclination. These results demonstrate that the current sheet flapping motion is a self-organized circulation process between the alternating hemispherical asymmetries of the nonadiabatic ion population inside the plasma sheet and the current sheet equilibrium itself.