Auroras filled much of the world’s skies for several nights in mid-May as a historic geomagnetic storm passed 100 kilometers overhead. Being able to see auroras so deep into the tropics was possibly a once-in-a-lifetime experience, but there will almost certainly be stronger geomagnetic storms later this year, giving aurora watchers around the world hope that it is there may be more dazzling lights. in the near future.
This is because we are rapidly approaching solar maximum, the peak of our star’s predictable 11-year activity cycle. Solar flares and coronal mass ejections, or CMEs, are most common during and just after solar maximum, and it is these that are responsible for the vivid auroras.
The aurora extravaganza of May 10, 2024, was the result of three CMEs emerging from the sun’s outer atmosphere and heading toward Earth. A CME is a collection of magnetized plasma ejected from the Sun’s exceptionally hot outer atmospheric layer, the corona, as a result of a disruption in the Sun’s magnetic field.
On May 10, each successive CME moved slightly faster than the last, allowing the three bursts of charged particles to merge before flooding Earth’s atmosphere. The combined energy of three CMEs impacting our planet at once unleashed an aurora show that will last for centuries.
AR3664 on May 10, 2024.Photography: NASA/SOHO
These CMEs were associated with Active Region 3664, a collection of relatively cool, dark sunspots on the sun’s surface that grew more than 15 times larger than Earth itself. You could see AR3664 without magnification simply looking at the sun through a pair of eclipse glasses.
It turns out that the enormity of AR3664 contributed greatly to our generational aurora display. These spots on the solar surface often alter the region’s magnetic field, creating instability and realignment that can force the release of a CME or even a powerful solar flare, a burst of electromagnetic radiation that can cause radio blackouts.
The sun’s surface rotates about every three and a half weeks, meaning sunspots are only visible from Earth for one to two weeks, depending on where they form on the solar surface.