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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)
qLJ
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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