Geoscience Reference
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Divergence of the field-lines in the magnetosphere decreases the magnetic
disturbance by 5-10 times.
The theory just described deals with the propagation of low-frequency
waves in the atmosphere and the ionosphere and also with ground and mag-
netospheric generation of magnetic variations by such waves. This theory only
reflects the basic features of this process, which under real conditions is much
more complicated. Actually, the wave propagates not in an isothermal at-
mosphere but in a medium with an intricate height temperature profile. This
profile can lead to the appearance of waveguides. As a result, a portion of the
wave energy can be trapped and carried away.
We now turn to results of magnetospheric observations of the strong
acoustic impact caused by an explosion on the ground.
15.2 Acoustic Shock Experiment
In 1985, acoustic action (Project MASSA
1
) has been proved to be a very
powerful tool for artificial generation ionospheric and magnetospheric per-
turbations. Acoustic action offers the possibility of simultaneous detection of
all elements of interest. In this project, in 1981-1982, the responses of the at-
mosphere, the ionosphere, and the magnetosphere to surface explosions were
studied (e.g. [2], [3], [4], [5], [6]).
The 251 tTNT blast was detonated on November 28, 1981, at 02h31m UT
(08h31m LT) at a point with coordinates 43
◦
48
N, 76
◦
51
E. The measurement
and monitoring equipment were located both in the immediate vicinity of the
blast (for the registration of shock wave, seismographs, and optical observa-
tions) and at distances of tens of kilometers from the blast: magnetometers,
acoustic measurements, Doppler units, ionosphere sounders. At large distances
from the blast (hundreds and thousands of kilometers), oblique and return-
oblique radio sounders were used on trajectories passing through the region of
the blast. Ionic probes in a high-frequency regime, magnetic measurements,
and measurements of incoherent scattering of radio waves, as well as other
observations were all made.
Virtually all of the instruments used in the experiment registered per-
turbations of geophysical parameters associated with the blast [2]. Based on
these findings, the following picture of the effects can be drawn. The shock
wave that was formed at a distance of 10 km from the blast converted into a
sound wave which was traceable along the Earth's surface up to a distance
of 2000 km. A portion of the energy of the acoustic wave traveling upward
was captured in the waveguide formed by the near-Earth temperature inver-
sion; then a partial reflection of the wave took place at altitudes of 40 km
and 100 km. However, the acoustic wave, carrying substantial energy, reached
1
Russian acronym for Magnetosphere-Atmosphere Relationships with Seismo-
Acoustics.
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