Measurements from the Wind spacecraft in the solar wind, the Geotail spacecraft in the magnetosheath, and multiple magnetometers on the ground are combined to study a unique electron flux modulation event in the magnetosheath that occurred during an interval of global Pc5 waves. The electron event is characterized by a Pc5-band oscillation occurring in the magnetic-field-aligned component of the electron flux (energy>38 keV) while the local magnetic field and plasma density remained unperturbed. During this event the whole magnetosphere oscillated as inferred from magnetic field recorded at the CANOPUS, IMAGE, and 210¿ MM chains. At the ground stations that are mapped to the dayside and duskside magnetosphere, we find a one-to-one correspondence of the peaks in the horizontal component to those in the electron flux. At the stations mapped to the dawnside magnetosphere the observed frequency is twice that of the electron flux oscillation. The time-lagged solar wind density and velocity at Wind were constant, which leads us to exclude the possibility that the waves were driven by ram pressure variations upstream of the bow shock. The Kelvin-Helmholtz (K-H) instability on the magnetopause is the more probable source of the Pc5 waves because (1) the solar wind velocity was ~730 km s-1, well above the average value; (2) the ground-based observations show that the Pc5 amplitude decreases with distance from the magnetopause; and (3) the dawnside and duskside magnetospheric flanks show oppositely polarized waves. The electron flux oscillation in the magnetosheath can be explained by intermittent magnetic connection between the spacecraft and the dawnside pulsating magnetopause. The ~60 keV protons are continuously streaming throughout the whole interval, providing evidence for a continuously active source and permanent leakage through a tangential magnetopause discontinuity. It is worth noticing that at progressively higher energies the energetic particle angular distributions are gradually more isotropic because at higher energies the particles are strongly scattered in the magnetosheath. ¿ 2001 American Geophysical Union