A very intense geomagnetic storm of class G4 has been underway since the night between 11 and 12 November, the penultimate on the scale that reaches up to G5, as confirmed by the Space Weather Prediction Center of the US agency Noaa.
It was triggered by the arrival of two coronal mass ejections, or CMEs, i.e. ejections of matter in the form of plasma, one of which was accompanied by the strongest solar flare of 2025 so far: the flare reached class X5.1 and the sudden explosion caused radio blackouts in Europe and Africa, disrupting high-frequency radio communications on the side of the Earth facing the Sun.
“The storm has been underway for several hours and had a very rapid onset,” Mauro Messerotti, professor of space meteorology at the University of Trieste, told ANSA. «It was caused by two CMEs arriving one after the other on November 11th and the arrival of a third CME is also expected, we will see how the situation evolves».
The sunspot indicated by the acronym AR4274, which has been very active in recent weeks and one of the most prolific producers of solar flares in the current solar cycle, has always emitted flares and Cme.
«The spot has gradually expanded and always presents a very high complexity from a magnetic point of view – confirms Messerotti – it is a very unstable energy reservoir». The storm lit up the skies with the colors of the auroras even at Italian latitudes, as demonstrated for example by the images taken at Plan de Corones in Trentino Alto-Adige, in the south-eastern Alps.
In addition to the fascinating phenomenon of auroras, however, G4 class events can cause problems with electrical infrastructures, can change the orientation of satellites in orbit and interrupt radio communications and satellite navigation systems.