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Response of propagation of ELF electromagnetic waves through the morning ionosphere to small density variations caused by infrasonic wave
We consider the problem of the effect of small plasma density variations on the propagation and
reflection of ELF (extremely-low-frequency) electromagnetic wave incident on the morning ionosphere
from above. Modifications of the electromagnetic wave field near the Earth surface and coefficient of
wave energy reflection from ionosphere caused by infrasonic wave are studied. The greatest
modifications of the field on the Earth surface and reflection coefficient are related to the density
perturbations at altitudes of strong electromagnetic wave attenuation (80–110 km). Reflection of
electromagnetic waves is especially sensitive to the plasma density perturbations if the value of horizontal
refractive index is close to a unit. In this case, modulation percentage of reflection coefficient can exceed
the modulation percentage of density in the infrasonic wave by an order of magnitude. The parametric
influence of plasma density perturbations in an infrasonic wave on the ELF electromagnetic field is
analyzed. If the values of the horizontal wave numbers of the electromagnetic and infrasonic waves are
close to each other, the field of the electromagnetic wave near the Earth surface can increase several
times. The obtained results are important for understanding the interconnection of ionospheric wave
processes of different nature. The study of the modulation of coefficient of ELF reflection from the
ionosphere is relevant for explaining the operation modes of a plasma magnetospheric maser.