Red auroral arc in the sky over Finland

All probably know about the auroras green and purple lights dancing in the sky during geomagnetic storms. But have you ever heard of SAR-arcs? Stable auroral red arcs (Stable Auroral Red arcs) was discovered in 1956 in the beginning of the space age and since then hundreds of times recorded by the cameras of satellites.

Most observers of auroras never seen them, because they are usually invisible to the human eye. But Matti Helin the night before was lucky enough to capture one of them in the South of Finland.

"SAR-arc was visible to the naked eye for nearly 30 minutes, and after the disappearance of another hour and a half remained visible for my camera. Usually we see auroras in the North, but this arc appeared to the South."

This phenomenon is associated with auroras, but it is not the same thing. Regular auroras appear when high-energy particles fall along polar magnetic field lines, crashing into the atmosphere (at an altitude of 100-200 km) and causing it to glow. SAR are formed differently. They are a sign of leakage of thermal energy to the upper atmosphere (at an altitude of about 400 km) from the circular system of currents of the Earth. Typically, SAR become visible to the naked eye only during a strong geomagnetic storms. Last night there was a storm of class G1, far from strong, but nevertheless arc appeared — another proof that the glow is full of surprises.

Translated by «Yandex.Translator»