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where
∆Φ
∆k
.
x
0
≈
The amplitude maximum is displaced northward by a value on the order of
x
0
. The direction of the displacement is determined by the sign of
∂Φ/∂k
.
k
x
-dependencies of the phases of transfer functions for electric and magnetic
fields show an appreciable difference. This also leads to a relative displacement
in the spatial distributions.
Changes of the geoelectrical parameters of the model will first affect the
E
(
g
)
x
(
x
) dependence. On the other hand, the
b
(
g
x
(
x
) maximum po-
sition depends slightly on the
ρ
(
z
) variations. For example, for a cross-section
that includes a layer of high resistance (
ρ
1
=10
4
Ohm
(
x
)and
b
(
g
)
y
·
m
,h
1
= 200 km;
ρ
2
=0
,h
2
=
) and resonance period
T
= 100 s
,
the displacement of the
electric component maximum is
∞
≈
100 km and
≈
30 km for the magnetic com-
ponent.
Z
g
tends to
Z
0
for highly conductive ground if the horizontal scale is
larger than the ground skin depth (see (11.23)). Let us introduce the so-called
'apparent resistivity'
ρ
ap
or
ρ
ap
associated with
Z
0
or
Z
g
by
ρ
ap
=2
T
Z
g
2
.
2
,
ρ
ap
=2
T
|
Z
0
|
(11.26)
ρ
ap
is frequency-dependent. For a frequency
ω
a layered geoelectrical cross-
section has the same surface impedance as the homogeneous half-space of the
resistivity
ρ
ap
(
ω
). The applicability of the model of the plane normally in-
cident wave can be checked by comparing curves
ρ
ap
(
T
)and
ρ
T
(
T
). Upper
panel of Fig.11.7 presents
ρ
ap
(
T
) (solid line) and
ρ
ap
(
T
) at observation lat-
itudes of
Φ
=60
◦
(long dashed) and
Φ
=55
◦
(short dashed) with resonance
periods of 100 and 46 s, respectively. The low panel of Fig. 11.7 shows phase
curves of
Z
0
and
Z
g
.
It can be seen that taking into account the field's pe-
culiarities near the resonance shells results in the appearance of additional
extrema for both high-latitude and middle-latitude observations. Deviation of
ρ
ap
(
T
)from
ρ
ap
(
T
) reaches 30% for the high-latitude curve and is caused
by the displacement of
E
(
g
)
y
(
x
)and
b
(
g
x
(
x
) with respect to each other. The
appearance of such peculiarities on curves
ρ
ap
(
T
) should always be expected
on the FLR-frequencies of the observation point. Anomalies in
ρ
ap
(
T
)in-
crease significantly in transition to high-resistance cross-sections without a
sedimentary cover.
Pc
3,4 pulsation fields on the ground within a 500 km zone along the FLR-
shell cannot be approximated with linear functions. Here the interpretation of
MTS-observations within the framework of traditional conceptions may result
in erroneous conclusions. Special caution is needed in interpreting sounding
data on high-resistance cross-sections without a sedimentary cover. To obtain
a reliable result it is necessary to find the spatial structure of the pulsation
fields (see Sect. 11.2).
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