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Fig. 6.8
Large-scale ULF pulsations observed at the geomagnetic observatories Wingst (Wn),
Göttingen (Gt), and Fürstenfeldbruck (Fu). H and D components of the magnetic variations are
displayed in the upper and bottom panels, respectively. Taken from Voelker (
1962
), and Glassmeier
(
1995
)
Wilson
1968
). This property keeps partly for the case of Pc4 pulsation. It should
be noted that at the latitudes below 50
ı
60
ı
these pulsations can be masked by
the global magnetic variations with time-independent period. The fundamental Pc5
pulsations occur primary in the sunlit hemisphere. This asymmetry probably arises
from magnetospheric structure asymmetries, which result from the existence of the
magnetotail and the plasmospheric convexity in the nightside magnetosphere.
The damped-type Pc3-Pc4 oscillations of global extension are illustrated in
Fig.
6.8
(Voelker
1962
). These oscillations with latitude-dependent period have
been recorded at three ground-based stations located at Wingst (the northernmost
station), Göttingen, and Fürstenfeldbruck (the southernmost station). The increase
of the oscillation period with L is compatible with the above analysis. The typical
amplitude of the Pc4 pulsations varies within 5-20 nT while the Pc3 amplitude is
smaller than 10 nT.
Other kind of the damped-type oscillations is shown in Fig.
6.9
(Glassmeier
1995
). The H-component of the geomagnetic variations caused by a magnetospheric
substorm is displayed at the upper panel. The sharp decrease of the magnetic field at
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