Abstract: Features of the mid-latitude geomagnetic index ASY-Hduring periods of the magnetosphere-ionosphere coupling are analysed. They are compared with feature of the auroral electrojet(AE) index and that of the equatorial electrojet.Both the results of the courrelation analysis and the superposed epoch analysis can be brought into a self consistent physical picture.It is also shown that the diurnal variation of the equatorial electrojet during the main phase of a geomagnetic storm with Revent is different from that on disturbed days when no energy injects into the ring current.All these results prove that it is'important to distinguishs.the effect of magnetospheric disturbance penetrating directly to mid- and lowffetitude from that generated in the ionosphere by dynamic processes.