Geoscience Reference
In-Depth Information
E
z
, V/m
3000
1
1000
2
0
-1000
0
4
8
t
, s
Fig. 11.12
Electric signals caused by aerial wave propagation in the surface atmospheric layer.
The signals were measured at the distances (
1
)1.5kmand(
2
) 2.8 km from the detonation of HE
with mass 500 t (Soloviev and Surkov
1994
)
11.2.4
Effect of Aerial SWs Propagating in a Surface
Atmospheric Layer
A sharp narrow spike in the initial portion of signal shown in Fig.
11.10
took
place several seconds after the detonation at the moment of aerial SW arrival at
the ground-based station. The electric perturbations caused by the seismic wave
propagating in a conductive ground are lower than this spike because the amplitude
of seismo-induced effect at the distance 1:5
D
2 km is about several V/m
(Chaps.
7
and
8
). Figure
11.12
illustrates the initial portion of the signals measured
at the distances (1) 1.5 km and (2) 2.8 km from the detonation site (Soloviev and
Surkov
1994
). As is seen from this figure, the front of geoelectric field perturbation
approximately propagates at the velocity of aerial wave. So, one may expect that the
source of electric variations is the local changes of pressure in the aerial SW.
Almost without exceptions the atmospheric air contains the heavy ions and
aerosols which may be both the neutrals and also the charged particles (e.g., see
Chalmers
1967
; Wåhlin
1986
; Sorokin
2007
). It is common that the spatial electric
charge in the surface atmospheric layer is about 10-500 pC/m
3
. Taking into account
that the total number density of the heavy ions is on the order of 5
10
5
10 m
3
,
the heavy ion excess is estimated as 10
8
-10
9
m
3
. Hence the perturbations of the
geoelectric field are induced by the changes in the spatial electric charge which is
formed by the heavy ions and charged aerosols.
The heavy ions play a crucial role in the formation of the atmospheric electrode
layer. However the aerosol particle may greatly affect the electrical parameters of
the atmosphere such as the composition and number density of heavy ions and the
structure of electrode layer. For the particles with size 0.01-0.2 m the aerosol num-
ber density is about 10
9
-10
10
m
3
in rural areas and 10
10
-10
11
m
3
near towns. The
enhancement of the aerosol density gives rise to an increase of the electrode layer
depth. Numerical simulations have shown that this depth can vary within 1-100 m
by the action of turbulent stirring of the air near the ground surface (Hoppel
1967
).
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