ULF-Waves on the Ground and in Space - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 53

Fig. 3.4. The variation of amplitude and the sense of polarization of Pc 5 seen at
high latitudes with latitude and longitude. After [77]

Pc 5 pulsations were discovered in the ionospheric plasma with the help
of polar radars, which made it possible to see the patterns for velocity
distribution in ionospheric plasma and in electric fields. Figure 3.6 presents
an instance of meridional distribution of pulsations at the ionosphere level ob-
tained with the help of the STARE radar system [106]. The system monitors
the drift of electron density perturbations in the E -layer under the action of
the wave electric field. The upper panel of Fig. 3.6 presents the coordinate
dependence of the value of the northern component of the electric field (cir-
cles), while the lower part shows the same for the phase (circles) [106]. The
solid line presents the fitted curves of the amplitude and phase. The region
of resonance enhancement of oscillation is clearly visible. The half-width of
the resonance region for Pc 5 oscillations at high latitudes is about 0 . 5 ◦ or the
first tens of kilometers.
High-latitude profile observations of Pc 5 geomagnetic pulsations [56] as
well as radar measurements of ionospheric plasma drifts point to the exis-
tence of a line spectrum. The 1 . 8 , 2 . 4 , 3 . 1 mHz frequencies dominated ([60],
[107]). Similar results were obtained by comparing F -layer drifts and ground
pulsations [77]. Pc 5 appeared mostly in the local morning. The typical dura-
tion of the oscillations was 3 , 4 h with surprisingly stable frequencies, changes
in which did nor exceed 5 10% and did not change from day to day and from

month to month ([77], [106]). The power spectra of the Doppler velocities had
four peaks: on 1 . 3 mHz frequencies near 71 . 5 ◦ ,on1 . 8

−

1 . 9 mHz at 70 . 5 ◦ ,on −

2 . 7 mHz at 69 . 75 ◦ and 3 . 3 3 . 4 mHz at 69 . 0S ◦ . −