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system. The solution of this problem given by Eqs. ( 5.29 ) and ( 5.32 ) describes the
potential function ‰ in the atmosphere. Substituting this potential function into
Eqs. ( 5.111 ) and rearranging, we obtain
B 0 F 0 O z C i k ? =k 2
?
b D
;
(5.68)
3
where the functions LJ 3 , F 0 , and q are given by Eqs. ( 5.31 ), ( 5.33 ) and ( 5.34 ).
Now we suppose that the acoustic perturbations in neutral gas propagate
horizontally with constant speed U parallel to the wave vector k 0 .Thevalueof
U can be close to the velocity of IGW at the altitudes of E-layer. For the sake of
simplicity, we assume that the mass velocity of the neutral gas flow has the following
form:
V D V m exp Œi k 0 . r U t/;
(5.69)
where V m is the amplitude of the neutral gas variations and r is a position vector
perpendicular to the vertical z axis. For a large-scale flow pattern the neutral gas
should be considered practically incompressible, i.e., r V D 0 (Kelley 1989 ).
Hence, k 0 V D 0 so that k 0 is orthogonal to V .
A temporal Fourier transform of Eq. ( 5.69 ) is given by
V m exp .i k 0 r /
i .! k 0 U / :
v .!; r / D
(5.70)
A spatial Fourier transform of Eq. ( 5.70 ), v .!; k ? /, has the pole which corre-
sponds to k ? D k 0 . The magnetic field b .!; k ? / is proportional to v .!; k ? / and
thus Eq. ( 5.68 ) contains the same pole. Performing an integration of Eq. ( 5.68 ) over
k ? gives the inverse Fourier transform of the magnetic field, that is b .!; r /. To study
the contribution of the pole k ? D k 0 into this integral, one should take a residue of
Eq. ( 5.68 ) at this point. Then the function F 0 is reduced to the form
iL. k 0 V m / z LJ 1 Ǜ P
V AI .! k 0 U / :
F 0 D
(5.71)
Substituting Eq. ( 5.71 ) into Eq. ( 5.68 ) one can estimate the spectrum peaks caused
by the neutral gas flow at E-layer. The calculations of this spectrum at various
ionospheric and atmospheric parameters have shown a distinct SRS of the electro-
magnetic variations on the ground surface (Surkov et al. 2004 ). In making these
calculations the numerical values of the gas flow parameters were as follows:
V m D 50 m/s, U D 500 m/s, and k 0 = 0:01-0:02 km 1 . For the nighttime conditions
the magnitude of the first spikes was of the order of 30-100 pT/Hz 1=2 . This result
should be considered as only a rough estimate of the magnitude because the latter
strongly depends on k 0 , the source spectrum and on other parameters. For example,
the increase in k 0 results in the decrease of the power spectra and the magnitude
 
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