Aurora borealis, (rare) show in England and Germany. “Waiting for an even more intense one”- Corriere.it

On Sunday evening the sky gave a show in the high latitudes of Europe and America. Social media has been flooded with breathtaking images of theaurora borealis which has been seen flashing as far afield as great britain, ireland, northern parts of germany and france, and in the United States as far as Ohio, regions where night lights are not an exceptional fact but are not very frequent either (the same is happening at the South Pole with the southern aurora).

The solar flux

The aurora borealis up to unusual latitudes had been anticipated in recent days by sites specialized in space meteorology which, thanks to satellites that monitor solar activity, had seen the arrival towards the Earth of a coronal mass emission from the Sun which would have caused a geomagnetic storm by interacting with the Earth’s magnetic field that protects us from harmful charged particles emitted by our star. The flow would have caused a G2 level geomagnetic storm, capable of producing aurora borealis down to sub-normal latitudes. And so it was.

An even more intense one is coming

But, warn the same sites, a more intense one is coming for the night of February 27-28 which could reach level G3 and cause weak radio interference and some minor satellite problems. The new aurora could be felt up to latitudes of 50 degrees North, i.e. equal to those of Frankfurt and Brussels, halfway between Paris and London.

The Northern Lights motifs

Why is the aurora so intense? The polar auroras (northern and southern) are due to the interaction of the flow of charged particles periodically emitted by the Sun with the earth’s magnetic field. The Sun is affected by cycles of maximum and minimum particle emission activity that last about 11 years. Since the end of 2019, our star has entered cycle 25 (calculated starting from 1755) and is rapidly climbing towards the maximum of the cycle which will be reached in the second half of 2025. The closer we get to the maximum of the cycle, the more the number of sunspots and associated coronal mass emissions.

Colors

The spectacle of the polar auroras due to their colours. Color green produced by the interaction of solar particles with atomic oxygen in the upper atmosphere about 100-160 kilometers high, the color blue-violet from nitrogen atoms about 90-100 kilometers above the surface. Color red manifests itself only with very intense solar storms capable of exciting even molecular oxygen (O2) at an altitude of around 240 kilometers which give the typical blood red color to the night sky.

History

The northern lights were also known in antiquity, Chinese and Greek chronicles mention them, in rare cases they have also been observed in Italy. The term borealis aurora was coined by Galileo Galilei, the physical phenomenon was fully explained only at the beginning of the twentieth century by the Norwegian scientist Kristian Birkeland through the propagation of electric currents in Space originating from solar storms which interact with the atoms of the Earth’s atmosphere. But it was not believed and only in the 1960s, with the first satellites, was Birkeland’s theory proven to be correct. Birkeland was nominated for the Nobel seven times, but he never got it. It was obtained in 1970 by the Swede Hannes Alfvn, who resumed and improved Birkeland’s theories in the light of the new data obtained from satellites.