It is recognized that the continuous pulsations (Pc) in the magnetosphere a
re in general composed of many wave packets and that these wave packets are
separated by phase skips. Previous observations by multiple spacecraft and
ground magnetometer stations suggest that the phase skipping and packet st
ructure of pulsation signals are most likely due to impulsive wave sources
or the beating of waves. However, the magnetic field data alone have not le
d to an understanding of the propagation of these wave bursts. By using bot
h the electric field and magnetic field data of the ISEE 1 spacecraft, we f
ind that the Poynting flux of Pc3-4 pulsations in the outer magnetosphere h
as an impulsive nature. The direction of time-average Poynting flux changes
every several wave cycles, and the phase skips in wave signals, both in th
e magnetic field and electric field, are often found between two adjacent P
oynting flux bursts. Furthermore, the phase difference between the electric
wave and the magnetic wave indicates that Pc3-4 waves are generally not in
exact resonance, counter to the traditional field line resonance paradigm.
These observational results provide us with strong evidence that the "cont
inuous" pulsations in the Pc3-4 band are in fact maintained by a series of
pulses, and the phase skips in the wave signals are its natural consequence
. The direction of wave energy propagation and its implications are also di
scussed.