MHD After-Effects of a Sound Impact - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 409

in the middle latitudes is 50 mA/m. Thus, the field-aligned current I ∼

10 mA/m. Let the transversal scale be l ⊥ =10 4 m. Then the field-aligned
current density is j ∼

∼

2 . 5 µ A/m 2 . The measured magnetic pulse

≈ 100 nT and

10 µ A/m 2 .
It follows from the estimations that the directed electron velocity in the
observed thin Alfven current jet can exceed the electron thermal velocity.
This, in turn, can cause an anomalous longitudinal resistivity that can also
create a magnetospheric Alfven wave.
Independent of the question of whether or not the explanation given here
for the appearance of the strong MHD-wave in the magnetosphere is true, we
can say with confidence that the acoustic action on the ionosphere and the
magnetosphere is extremely effective in the sense of the artificial generation
of an MHD-wave. Moreover, the managed acoustic impacts are a significant
tool to study the isolated components and the entire chain of the intercon-
nected effects responsible for a transmission of the large-scale perturbations
in the medium surrounding the Earth: the atmosphere, the ionosphere and
the magnetosphere.

its transversal scale of 10 km give the longitudinal current j ≈

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