The dynamics of westward auroral electrojets in the course of magnetospheric substorms is studied according to the data of a meridional chain of magnetometers. It is shown that, during active phases of the substorm, the westward electrojet becomes inhomogeneous and some current filaments appear in it; some of them drift polewards, some other shift equatorwards. A method is proposed to estimate both the potential and curl parts of the magnetospheric electric field, the value of the electromagnetic energy entering the plasma sheet in the magnetotail, and the rate of Joule heating in the ionosphere based on data on the dynamics of the auroral electrojets.