| The plasma sheet in the magnetotail contains different ion species, where the H+
comes
from the ionosphere and/or the solar wind, whereas the O+ and He+ originate mainly
from the
ionosphere. The ion composition in the plasma sheet dramatically changes during the fast
flow
intervals. In this paper we used the Cluster data to compare the variations of O+, He+ and
H+
density in the plasma sheet during the fast flow intervals by applying the superposed
epoch
analysis technique. We found that after tail activities, the O+ density changed little while
the
densities of other species decreased much. Comparison between H+ and He+ showed
little
difference, which indicates that the behavior difference between O+ and other species is
mainly
due to the processes in the plasma sheet rather than the source difference between these
species. The lighter ions were flushed away towards the Earth and down tail while most of the
O+ remained in the plasma sheet. |