A statistical study of compressional waves in the tail current sheet -: art. no. 1429

A statistical study of the Cluster FGM data is performed on compressional waves for 68 selected 12 min intervals when the spacecraft are in or near the neutral sheet. The data are well distributed in local time between 2100 and 0300 LT. The compressional wave power is strongly dependent on the maximum plasma flow velocity (based on the CIS-CODIF data) during the 12-min interval. Up to a perpendicular flow velocity of similar to400 km/s the spectral power increases with velocity; at higher velocities the spectral power saturates. The turbulence measured in the frequency range between 0.08 and 1 Hz shows that on that scale the magnetotail has fully developed quasi two-dimensional turbulence. We relate the quasi two-dimensional (2-D) turbulence to the finite extension of the flow channel, with a streaming instability as its source. There is an asymmetry in wave power between the premidnight and midnight/postmidnight sectors. The plasma flow direction splits the data into two distinct categories, the Earth/duskward and the tail/dawnward flows.