“Stealthy CME” Sparks Geomagnetic Storm

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From Spaceweather.com


Sept. 13, 2023: (Spaceweather.com) An unexpected CME hit Earth’s magnetic field on Sept. 12th (1237 UT) and sparked a G2-class geomagnetic storm. Magnetically, the CME remained connected to our planet for more than 13 hours, allowing plasma from the CME’s wake to enter Earth’s magnetosphere. This fueled a display of auroras photographed as far south as Missouri (+40.2N) and Nebraska (+40.9N).

Matthew Merrell knew the storm was underway, and he waited anxiously for the sun to set over his home in central Minnesota. As darkness fell, he saw the auroras:

“It was a great start to the night with pillars visible as soon as the sky was dark enough,” says Merrell. “By 10:00 pm it was just a gentle glow with very little motion.”

Merrell witnessed only the subsiding tail-end of the storm, a G1-class event. At its G2 apex, the storm produced “BRIGHT” and “stunning” activity over Scotland, “massive rays” above Ireland, and an all-sky explosion of color over Iceland. Magnetometer needles in Britain swung wildly with more than 15 hours of dramatic undulations.

Forecasters did not see this coming. One surprised NOAA analyst called it a “stealthy CME.” In retrospect, it was probably one of many relatively bright CMEs that left the sun on Sept. 8th, shown here in a 24 hour time-lapse from the Solar and Heliospheric Observatory (SOHO):

When the sun spits out so many storm clouds in such a short period of time, it can be hard to disentangle them and figure out which one(s) might be heading toward Earth. Notably the movie includes a distinct halo CME. At the time it was thought to be a farside event, but maybe it is the one that hit Earth yesterday.

Did you miss the storm? Subscribers to our Space Weather Alert Service received instant text messages when the CME arrived and, later, when the geomagnetic storm began. Give it a tryAurora alerts: SMS Text