ULF-Waves on the Ground and in Space - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 58

133-117s

200-167s

KEY
H
D

L-VALUE L-VALUE

105-87s 80-69s

Fig. 3.10. Average wave phases relative to the phase at the northern station versus
L -value. The amplitude maximum of the latitudinal profile is marked by the solid
arrow. After [27]

( L =2 . 44 3 . 83). The plasmapause during all the three Pc 3 , 4 series was to the

north of the station array because of the low magnetic activity ( Kp

−

3+).
Figure 3.10 presents the latitudinal dependence of phase angles for various
frequencies in the pulsation spectrum calculated for three 2-hour series of
Pc 3 , 4 oscillations at each station measured relative to the phase at the most
northern observatory. It can be seen that the position of the maximum in the
meridional distribution of pulsations is shifted southwards with the increase
in frequency in accordance with the FLR-theory. The FLR-theory predicts
larger changes in H -component than in D -component across the amplitude
maximum. Moreover, phase was predicted to increase with decreasing latitude.
Examination of Fig. 3.10 indicates that the phase changes are in agreement
with these predictions.
The question of the lowest latitudes for which a noticeable role of FLR in
ground pulsations is worth mentioning ([59], [86], [95]). It is clear that at low
latitudes, the Q -factor of FLR decreases as a field line plunges into the high
conductive ionosphere. The resonance frequencies ω R ( ϕ ) have a minimum at
middle and low latitudes and grow near the equatorial region. Experimentally,

≤