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in gas-discharge devices, electrolytes, granulated resistance, germanium and silicon
diodes, photoelectric cells, contact resistances, thermistor, and etc. Surprisingly,
our understanding of the flicker-noise is not so good as it should be, given its
commonplace occurrence. This type of noise is supposed to be provided by a
superposition of a large number of random processes with different relaxation times,
including slow fluctuations of both the medium resistance and the source emissivity.
Here we assume the presence of the flicker-noise in the spectral density of
the ionospheric wind-driven currents. In such a case the mean current density in
Eq. (
6.103
) should be replaced by the mean height-integrated currents,
D
I
.
w
/
l
I
.
w
p
E
1=2
,
in such a way that Eq. (
6.103
) is transformed to
D
I
.
w
/
l
I
.
w
p
E
m=2
f
n
F
lp
.f /
D
K
;
(6.104)
Notice that if the currents I
.
w
/
l
and I
.
w
p
are uncorrelated, then the function F
lp
.f /
vanishes.
Substituting Eq. (
6.104
) into Eq. (
6.92
) gives an order-of-magnitude estimate of
power spectrum on the ground surface. For simplicity we choose the case F
xy
D
F
yx
D
0 and m
D
2 that gives
3Ǜ
2
H
g
3
C
g
3
D
I
.
w
x
E
2
Ǜ
2
H
g
3
C
3g
3
D
I
.
w
y
E
2
0
V
a
K
256d
2
f
2Cn
‰
.B/
xx
D
C
(6.105)
where
ǝ
I
.
w
/
Ǜ
stands for the mean amplitude of the height-integrated ionospheric
current, which can be estimated as
D
I
.
w
x
E
D
B
0
†
H
h
V
?
i
†
P
ǝ
V
y
Ǜ
sin ;
D
I
.
w
y
E
D
B
0
†
H
h
V
?
iC
†
P
ǝ
V
y
Ǜ
;
(6.106)
If the dispersion of the acoustic wave velocity is neglected, that is, V
a
is a constant
value, then the spectral density ‰
.B/
xx
.f / is inversely proportional to f
nC2
. Recently
Surkov and Hayakawa (
2007
) have found that the presence of flicker noise in the
atmospheric background current, can provide the same dependence of the ULF
power spectrum on frequency.
To make a theoretical plot of the spectral amplitude we use the numerical
values of the ionospheric and atmospheric parameters alluded to above. Taking
the notice that V
A
D
5
10
2
km/s is best suited in the altitude range of the E
layer, the ionospheric parameters Ǜ
P
D
3:14 and Ǜ
H
D
4:71 are chosen for
the daytime ionosphere while Ǜ
P
D
0:126 and Ǜ
H
D
0:188 for the nighttime
conditions. The mass velocity of the neutral gas in the ionosphere is estimated as
ǝ
V
y
Ǜ
h
V
?
i
V
a
10
2
m/s and the angle of magnetic field inclination
D
=2.
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