Millions of people saw the spectacular aurorae in May, when multiple coronal mass ejections hit our planet in the largest geomagnetic storm in decades. Tonight it looks like we might have a comparable spectacle, so if you missed that one you’ve got a chance to see it again.
The NOAA Space Weather Prediction Center has estimated that the Earth will experience a strong geomagnetic storm (G3 level). The one in May was originally classified as severe (G4) and then upgraded to extreme (G5) as it evolved. Aurorae are being expected at lower magnetic latitudes than usual, but maybe not quite as low as in May.
Predictions suggest that in the Northern Hemisphere, it could get as low as northern California in the US and Central Germany in Europe. In the Southern Hemisphere, the whole South Island of New Zealand, as well as Tasmania and the state of Victoria in mainland Australia, are experiencing the celestial live show.
The reason why we’re seeing more and stronger geomagnetic storms and flares is that the Sun is approaching its maximum. That is the peak of activity across its 11-year-long cycle. The maximum could literally be any day now (we only know after it has happened) and it is a period with more sunspots. These are slightly colder regions on the surface of the Sun where the magnetic field is particularly intense.
The extreme magnetic regions produce all sort of effects, such as solar flares and coronal mass ejections (CMEs). CMEs are large waves of plasma (electrically charged particles) thrown by the Sun into interplanetary space at high speed.
The particular high intensity of the upcoming geomagnetic storm is due to a cannibal CME, similar to that that hit in May. This happens when two or more CMEs merge into a single one. From the data collected by satellites, researchers can provide a bird’s eye view of the Solar System. It shows that two CMEs released on July 27 quickly merged into a single one.
The following day the Sun emitted a third CME. Eased by the wake of the first two, it was able to catch up with them and merge as well. There is a fourth one coming, emitted on July 29, but it will only merge after the waves of plasma have moved past Earth.
A particular active region on the Sun is the spot known as AR 3764. It released an X1.5 flare yesterday that caused radio blackouts across most of the sunlit side of Earth. Six other flares of weaker intensity (M-class) were recorded from the same region.
The sunspot responsible for the May event continued to create events for weeks, even messing with the robots and spacecraft on and around Mars.
