MHD After-Effects of a Sound Impact - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 408

employing powerful industrial explosions, confirmed the emergency of a 'noisy'
spot in the upper atmosphere over the blast point.
The observations of the ionospheric effects provoked by a blast of 4 . 8kT[8]
were carried out using a network with the slightly oblique Doppler sounding
and pulse vertical radio sounding units. The experiments demonstrated that
the acoustic front generates a small-scale turbulent structure. The excitation
of the ionospheric turbulence was observed both over the blast point and at
distances of the order of several hundreds of kilometers from it. At the sporadic
E s -layer a fragmentation of the inhomogeneities into a spatial-temporal scale
of 2-10 km and 1-2 s was observed.
Small-scale random inhomogeneities in the lower E-layer significantly in-
crease the effective Pedersen conductivity, Σ P . Theoretical consideration
and laboratory experiments of this problem have been discussed already in
Chapter 10, especially the relation of the increase with β e , possible reasons for
the heights of this effect and relative contributions to the integral Pedersen
conductivity. It follows from (10.37) that the ratio of the effective Pedersen
conductivity σ e P to the mean Pedersen conductivity σ P is given by

σ e P

= β e δN e .

σ P N e

10 2 at heights 90-100 km (see Figure 2.5). Then the ratio σ e P / β e ≈ 10.

Σ P of the perturbed layer increases in the order of magnitude. Contribution
of the undisturbed lower E -layer into the total integral conductivity of the
whole E -layer is

σ P ∼

≈

5-10%. Under changes of the lower ionosphere conductivity
10 times, its contribution into the integral Pedersen conductivity consists of
≈ 50%.

The flickering high-conductive ionospheric inhomogeneity results in an ap-
pearance of the longitudinal Alfven current (e.g. [19]) excited by the back-
ground electric field. Here we examine the field-aligned current arising at the
perturbed ionosphere region. Let the acoustic wave causes

50%, i.e. δΣ P / Σ P ≈

10% perturba-
tions δN e of the electron background ionospheric concentration N e 0 .
The transversal inhomogeneity results in the ionospheric current redistri-
bution, part of them flows out the ionosphere along the geomagnetic field.
The ratio of the total field-aligned current I outflowing from the perturbed
region to the background horizontal ionospheric current I 0 is

∼

∼

I I 0

Σ A
Σ A + Σ P 0

δΣ P
Σ P

,

where Σ A = c 2 / (4 πc A ) is the Alfven wave conductivity; Σ P is the effective
integral conductivity of the ionospheric layer perturbed by the acoustic wave;
Σ P 0 is the undisturbed ionospheric integral Pedersen conductivity; δΣ P =
Σ P − Σ P 0 . The background integral current I 0 in the middle latitudes is

∼ Σ P 0 since the experiment has been performed during

the early morning. Then I ∼

0 . 05 A/m. Let Σ A ∼

0 . 25 I 0 . The background integral current I 0