Current Sheet Structure and Motion Observed by Cluster on September 15, 2001

Multiple crossings of the neutral sheet were observed by the Fltax Gate Magnetometer （FGM） and the Cluster Ion Spectrometry experiment （CIS） onboard the Cluster li at （-19, 4,-1） Re from 0430 UT to 0515 UT on September 15, 2001. The high-speed proton flow, which reversed from tailward to Earthward, was detected during the multi-crossings. Using a linear gradient/curl estimator technique the cross-tail current was obtained. The peak of the current density reached 28 nA/m^2. A large-scale wave propagating duskward and the thin current sheet flapping in the vertical direction were investigated, the thickness of the current sheet ranged from 0.3 Re to 0.2 Re, and had a tendency of being thinner. The velocity of the proton bulk flow in the x direction exceeded 1000 km/s during the magnetic field reconnection. By using the multi-point timing analysis and Minimum Variance Analysis, the structure and motion of the magnetotail current sheet were estimated.