We studied the ULF wave packet propagation in the Earth plasma sheet making use of the magnetic field measurements from FGM detector and plasma properties from CORRAL detector aboard the Interball-Tail spacecraft. The MHD vortex structures were observed simultaneously with the Pc5 ULF waves. The vortex spatial scale was found to be about 1200-3600 km and the velocity is 4-16 km/s transverse to the background magnetic field. We
studied numerically the dynamics of the initial vortex perturbations in the plasma system with parameters observed in the Earth plasma sheet. The system with the vector nonlinearity was processed making use of the full reduction scheme. The good agreement of the experimental value of the vortex structure velocity with numerical results was obtained. The velocity was found to be close to the local plasma drift velocity
