Strong Geomagnetic Storm

A co-rotating interaction region (CIR) hit Earth on May 29th, sparking a strong G3-class geomagnetic storm with auroras in both hemispheres. Gregory Ash photographed the display from Ely, Minnesota:

"The aurora was very diffuse for the first hour, then it finally exploded with huge pillars that backlit this tiny island," says Ash.

CIRs are transition zones between fast- and slow-moving streams of solar wind. They contain CME-like shock waves that do a good job sparking geomagnetic storms and auroras. We knew this CIR was coming, but expected it to produce no more than a minor storm. The G3 strength of the storm was a surprise to forecasters.

Source: https://www.spaceweather.com/