Rare forms of Aurora Borealis

12th of December a minor geomagnetic storm was actively producing auroras at the observatory. My all sky cameras recorded two different, very unusual forms of auroras. First, a rare form of proton auroras appeared. These could be also called EMIC auroras. Electromagnetic ion cyclotron (EMIC) waves are plasma waves that originate near Earth’s magnetic equator in space. They form when fast-moving, hot ions circling the planet cross into regions of cold, dense plasma surrounding Earth. This interaction creates an instability between the hot and cold plasma, which generates EMIC waves. Once formed, the waves travel along Earth’s magnetic field lines from the equator toward higher latitudes. EMIC waves can disrupt Earth’s radiation belts. As they move through space, these waves can knock ions and electrons out of stable paths, sending them into Earth’s atmosphere. These protons produced pulsations in the proton aurora, occurring on timescales of tens of seconds.

Proton auroras captured in the observatory all sky camera

In this timelapse you can see how the proton auroras move rather fast and sporadically in the sky

After this rather unusual event, the first appearance of dune aurora forms appeared. This event is unlinked to proton auroras seen just few hours earlier. Dunes are a form of aurora that appear at an altitude of approx. 100 kilometers and is believed to be caused by atmospheric waves creating denser pockets of oxygen atoms, forming a pattern of waves in the sky. This form of auroras was first spotted by Finnish aurora enthusiasts and was later studied by University of Helsinki. You can see them on the bottom right of the allsky image below, forming a wave pattern in the otherwise even field of glow from the Northern lights.