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In-Depth Information
If the typical length
C
of the aerial wave is much smaller than the width l of
the electrode layer, then the model is reduced to the field of a charged thin lateral
strip and its electrical mirror image in the conducting ground. In this case we get the
following simple estimate of the electric field amplitude on the ground surface
0
C
V
C
ln .l=
C
/
"
0
U
E
max
:
(11.34)
In the inverse extreme case when
C
l, the problem is reduced to the field
of a plane condenser generated by the charges of the atmospheric electrode layer,
which is pressed by the SW, and the opposite charges induced in the ground. The
solution of this simplified problem is given by
E
max
0
lV
C
=."
0
U/:
(11.35)
It should be noted that the exact solution of the problem derived by Soloviev and
Surkov (
1994
) on the basis of Maxwell equations and Eq. (
11.31
) can be reduced to
Eqs. (
11.34
) and (
11.35
) in the above extreme cases.
It follows from the observations that the amplitude of the electric field variations
is approximately proportional to the parameter
C
V
C
and this tendency keeps
for different normalized distances and masses of explosives. It appears that the
case of short aerial wave .
C
l/ occurs in practice. Substituting the following
numerical values
0
D
8-80 nC=m
3
,
C
D
10 m, V
C
D
35 m=s, U
D
350 m=s and
l
D
10
2
m into Eq. (
11.34
) we obtain E
max
D
0:2-2 kV=m. Both this estimate and
experimental data shown in Fig.
11.12
are found to be of the same order. It should
be noted that the shock compression may result in the release of ions which are in
bound state. This leads to the enhancement of the charge density in the SW which
results in the increase of the electric field amplitude.
11.2.5
Ionospheric and Magnetospheric Effects
As noted in Chap.
10
, the aerial waves is the most efficient way to transfer the energy
from the EQs and strong explosions to the ionosphere.
When the aerial SW enters the ionosphere, the entrainment of the ionospheric
plasma with neutral flow results in the generation of ionospheric currents and local
perturbations of the Earth magnetic field. One of the pioneering studies possibly
related to the excitation of the ionosphere by SWs was the variations of the
geomagnetic field observed at Irkutsk magnetic observatory after the detonation of
Tunguska meteorite in 1908 (e.g., see Ivanov
1961
). The abnormal behavior of the
geomagnetic field has been observed 2.3 min after the detonation and lasted for
several hours.
Considerable attention has been paid in the past to the study of man-made
excitation
of
the
ionosphere
by
the
SWs
produced
by
atmospheric
nuclear
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