Scientists have described a possible cause of the green glow in the sky

A group of Russian scientists from the Higher School of Economics, ICI RAS and IZMIRAN described the development of modulation instability of electromagnetic waves in the dust plasma of the ionosphere, which occurs at high intensities of electromagnetic radiation. The researchers took into account inelastic collisions of ionospheric plasma particles, and also formulated new tasks and applications that need to be considered in the future.

The results of the study are published in the journal Physics of Plasmas. The modulation interaction is important for the explanation of various natural phenomena. This is a key process in the transition of a plasma from a state of weak to a state of strong turbulence. With weak turbulence, the waves in the plasma behave chaotically, but they do not correlate well with each other, in contrast to strong turbulence, when the interaction between them is significant, as a result of which strongly correlated structures (solitons, cavitons, filaments) are formed, magnetic fields are generated, heating and effective acceleration of particles occur.

In a previous work in 2009, scientists studied the possibility of the development of modulation instability in the ionospheric plasma at altitudes from 80 to 120 km in the presence of high-speed meteor showers. It turned out that meteor showers lead to the formation of dusty plasma at these altitudes, which, in turn, has a significant impact on the nature of the flow of nonlinear processes in the plasma.

In the new study, the authors note the important role of inelastic collisions of neutrals (neutral atoms) with electrons and ions of the ionospheric dust plasma. At the same time, the influence of modulation instability on the propagation of electromagnetic waves in dusty ionospheric plasma is very important at altitudes of 90-120 kilometers. This is the height of the dense layers of the atmosphere at which spacecraft are heated. Getting to these heights, meteoroids evaporate, after which the meteoric substance condenses, and small particles are formed, which become part of the dust plasma.

The modulation instability in the dust plasma affects the low-frequency region of the electromagnetic noise spectrum, contributes to the generation of infrasound waves that can reach the Earth's surface.

"Infrasound waves can be excited due to volcanic eruptions, earthquakes, flights of supersonic aircraft, explosions on the ground, and so on. In this regard, it is important for us to understand the nature of the sources of infrasound, which allows us to understand its origin, " says the author of the article, professor of the Faculty of Physics at the HSE, head of the laboratory of the ICI RAS Sergey Popel.

The modulation interaction at altitudes of 110-120 kilometers allows us to explain the increase in the green glow in the sky at a wavelength of 557.7 nm. It leads to the generation of dust sound waves, which are unstable at altitudes of more than 110 kilometers, as a result of which vortices are formed. Those, in turn, mix the substance at different heights — conditions appear for chemical reactions accompanied by the release of photons. It is they who manifest themselves in the form of a green glow of the sky.

Also, the modulation interaction leads to the formation of inhomogeneities of electron and ion concentrations in the ionosphere during the operation of high-power heating stands, such as HAARP, EISCAT and others. In addition, the authors of the article studied the dust plasma of meteor tails. It turned out that in this case, the modulation interaction explains the observed effects, for example, electrophone noises during the passage of meteors.

"Our results are important for explaining and describing natural phenomena in the ionosphere and the Earth's atmosphere, in particular, the propagation of electromagnetic waves at altitudes from 90 to 120 kilometers. It is planned to continue research on the effect of modulation excitation of inhomogeneities in the ionosphere during the operation of such installations as HAARP, EISCAT and others that affect the state of the Earth's atmosphere," comments Sergey Popel.