ULF-Waves on the Ground and in Space - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 60

Connection of the Pc 3 , 4 Frequency with the IMF

The dependence of the Pc 3 , 4 pulsation period at middle-latitude observato-
ries on the magnitude and direction of Interplanetary Magnetic Field (IMF)
was discovered in 1971 [101]. Inverse dependence of Pc 2 4 pulsation frequen-

cies on the magnitude of the IMF was shown: Direct measurements of wave
frequencies and IMF values in the upstream region ([35], [73]) confirmed the
results of the ground-based studies:

−

f (mHz) ≈ 5 . 7 × B IMF (nT) .

It was suggested that the origin of these pulsations is extra-magnetospheric.
In the proposed generation mechanism, the ion downstream of the solar wind
flowing around the magnetosphere is reflected from the bowshock. An arising
upstream ion flow propagates along the IMF and excites ion cyclotron instabil-
ity. The instability causes FMS-waves, whose frequency is determined by the
ion cyclotron frequency in the solar wind ([29], [48]). Correlation analysis of
the low-latitude Pc 3 pulsations ( L =1 . 3 1 . 8) and the oscillations of the same

frequency range detected by the synchronous satellite GOES 2 ( L =6 . 67) also
confirmed the linear dependency of the frequency on the strength of the IMF
( B IMF )intheform

−

f (mHz) ≈ 6 . 0 × B IMF (nT) .

Satellite Measurements of the Pc 3Waves

Simultaneous events of Pc 3 , 4 pulsations on the ground and in the magne-
tosphere were found in ([65], [92], [103], [109]). The waves were observed at
the same time in Space and on the Earth at the same frequency and with simi-
lar wave forms. Both compressional and transverse oscillations were identified
in the satellite magnetic measurements. A close correspondence between the
compressional component and the ground signals was observed. These results
confirmed that Pc 3 , 4 waves were transported through the magnetosphere by
the FMS-waves.
Takahashi et al. [96] traced the Pc 3 wave package from the outer magne-
tosphere to the ground and observed a case of simultaneous Pc 3 oscillations
inside the magnetosphere and at a meridional chain of high-latitude stations.
There a time interval was selected during which the AMPTE CCE satellite
was located near the subsolar magnetopause. The data came from five sta-
tions: three in Iceland ( L 6), a station conjugate to Iceland in Antarctica,

and another station at the average cusp latitude. The stations were located
almost at the basis of the filed line on which the satellite was placed.
Observation results are on the whole in agreement with the above-described
scenario for the generation and propagation of hydromagnetic waves in the

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