We have determined a characteristic of Pc 5 pulsation in the morning sector by use of ground magnetometer and riometer (cosmic noise absorption) data, in conjunction with data acquired with satellites which include the magnetic fields above the ionosphere and electron fluxes at geosynchronous orbit. We have found that the onset of a flux increase in energetic electrons of 30 keV to 200 keV at geosynchronous orbit almost coincides with the onset of Pc 5 pulsation activity and riometer absorption on the ground. We have ascertained that when the Pc 5 pulsation occurs on the ground, the large-scale Birkeland current system observed at ionospheric altitude splits into a number of small-scale Birkeland current pairs. We could infer that the electron flux enhancement, presumably supplied from the tail plasma sheet associated with the substorm onset, provides stress to cause the background large-scale plasma vortex to split into the small-scale vortices propagate along the field lines and sustain the standing Alfvenic oscillations at several different, but neighboring shells of the field lines. ¿ American Geophysical Union 1992