Oct. 12. 2021: It’s been a while. Last night, auroras were sighted in more than a dozen US states after a CME struck Earth’s magnetic field. “The G2 geomagnetic storm produced the first visible auroras from coastal Massachusetts since 2017,” reports Chris Cook, who snapped this 30-second self portrait around 1am EDT on Oct. 12th:
The red-topped auroras Cook witnessed are relatively rare; they appear during geomagnetic storms that spread far from the poles. Red is caused by oxygen atoms meeting the solar wind as high as 500 km above Earth’s surface.
In some states the auroras were so bright onlookers photographed them using nothing more than their cell phones. iPhone or Android? You decide:
The iPhone photo on the left comes from Tyler Knight of Mound, Minnesota, while the Samsung Galaxy image on the right was taken by meteorologist James Sinko on Castle Hill, Maine. Across the border in Saskatoon, Canada, Frank Lang recorded a must-see video using his iPhone 12.
At the apex of the storm, auroras descended as far south as Nebraska. Caryl Bohn photographed their faint red glow from the town of West Oak.
Subscribers to our Space Weather Alert system were notified the instant the CME hit. The alert was triggered by a sudden uptick in solar wind speed signalling the arrival of a shock front:
The plot shows data from NOAA’s DSCOVR spacecraft. When the CME passed by, the solar wind quickened by 120 km/s. At the same time, the plasma density tripled, and the temperature increased almost 10-fold. These are classic signs of a direct hit by a CME.