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Sometimes the usual - multi-colored - aurora borealis are accompanied by bright white flashes, the nature of which was still clear. Now, thanks to increasingly sophisticated technology, it was possible to record dozens of such unusual cases. It turned out that these white glows are similar to another spectacular atmospheric phenomenon called "Steve".
The aurora borealis is a product of the solar wind, that is, a flow of its own substance that constantly flies away from the luminary: protons, electrons, and even entire helium nuclei. Basically, the large Earth's magnetosphere restrains all this bombardment hundreds and thousands of kilometers above the planet, but it has two vulnerable places: the North and South Poles. The lines of force of the Earth's magnetic field emanate from one of them and, having bypassed the world, enter the other pole. Therefore, it is there that the charged particles of the Sun get the opportunity to meet with denser layers of the atmosphere.
Atoms and entire molecules in the atmosphere temporarily enter an excited state from this attack: the electrons floating around their atomic nuclei move to higher "orbits." Soon they return to their previous levels, but not without visible consequences: at the moment of the reverse movement of each electron, a photon is emitted. Hence the glow. Its color depends on the specific substance attacked by solar particles, as well as on the altitude: for example, oxygen at altitudes of about 100 to 300 kilometers glows green, higher red. Blue and purple shades are from nitrogen at relatively low altitudes.
In any case, auroras are mainly colored, but sometimes they have white or grayish-white light streaks. No clear explanation has yet been offered for them. As you know, white light combines the entire visible spectrum, that is, all possible wavelengths of visible light. Recently, a team of scientists from Canada and the USA decided to clarify the nature of these unusual auroras.
In an article for publication Nature Communications. researchers summarized the observations of 30 such cases and drew attention to the fact that these glows are very similar in their characteristics to another no less interesting atmospheric phenomenon — the so-called Steve. It is a spectacular, bright white-violet streak that stretches for hundreds of kilometers and crosses a considerable part of the night sky.
She was named "Steve" actually as a joke, recalling an episode from a popular cartoon where the characters decide to name a new unknown phenomenon that way. Later, NASA decided to "legitimize" this term and proposed to use it as the abbreviation STEVE - Strong Thermal Emission Velocity Enhancement.
Physicists concluded that such a band of light comes from a very hot flow of gas at an altitude of about 300 kilometers above the Earth. It is interesting that Steve was discovered by researchers of the aurora borealis, and they suspect that it is the same consequence of the influence of solar particles on the atmosphere, only connected not with the excitation of atoms, but with heating.
A similar mechanism of occurrence has now been proposed for white and gray-white inclusions in the aurora borealis. According to scientists, it could be chemiluminescence — a glow due to chemical reactions, in this case triggered by extreme heating of the upper atmosphere. As the researchers emphasized, the aurora borealis turned out to be a much more complicated process than expected.
