Dynamical Structure of the Cross-tail Current Sheet During Substorms Observed by Cluster

We report on the dynamical variation of the current sheet structure in the magnetotail using magnetic field and plasma data obtained by the Cluster multi-satellites. It is found that in some cases the thickness of the cross-tail current sheet shows temporal variations repeatedly. This sausage-mode-like variation is associated with substorm onsets or occurrence of fast plasma flows, with the time