Inhomogeneous Ionosphere - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 290

Fig. 9.8. Daily variation of the orientation angle (in degrees) of the pulsation
horizontal magnetic field for pulsations within three different ranges T< 50 s;
50 <T < 150 s and 150 <T < 500 s. The equatorial observatory Huancayo,
04/25/1986

For the same date (04/25/86) the time dependence of the logarithm of the
H -component power was studied within the frequency range 0 − 0 . 06 Hz. The

largest intensity found was recorded for long-period T 500 s oscillations

with clearly expressed diurnal variations of the H -component values with a
maximum at noon, and with an abrupt fading before sunrise. Maximal inten-
sity of the oscillations with periods T

∼ 150 −

150 s . Pulsa-
tions with T< 50 s fade abruptly. Despite the significant scattering behavior
of the pulsation intensity with T< 50 s and T> 150 s a clear (

∼ 50 − 150 s is closer to T ∼

45 ◦ ) anomaly
was found in the orientation angle. The orientation angle anomaly corresponds
mainly to 50 s oscillations and to oscillations with periods 130

≈

140 s.
To summarize one can conclude that oscillations within the range 50

−

− 500 s

are generated by Alfven waves. Shorter T 40 s oscillations are generated by

FMS-waves. A more detailed analysis of the experimental data indicates that

≈