May 29, 2025 Auroras

Itasca County, MN

A corotating interaction region (CIR) and high speed solar wind stream arrived during the late afternoon and evening, generating a G3 geomagnetic storm (a 3 on a scale of 1 to 5 for geomagnetic storming). Usually, G3 can bring auroras overhead and into the southern sky, and this time was no different, except that the G3 storming occurred before sunset with Bz bottoming out briefly at -25 nT. After sunset, the conditions calmed down to about G1 or G2 with Bz hovering a few nT either side of zero. If the auroras weren't overhead as soon as it was dark enough to see them, then they'd probably be just on the northern horizon for the rest of the night. It turned out I was slightly wrong with this prediction.

Plot of the solar wind data during the event.

Given that we had some clouds, and we were to the north of a closed upper low, the clouds were clearing from northeast to southwest, and if I drove northeast, I'd have better sky conditions than if I stayed closer to home. I had quite a bit on my plate at work this week, so I initially thought it was not worthwhile to drive this far, but I had decided my route pretty quickly and definitively, so I continued onward. It had been a few years since I had been to this location, and I forgot that it takes pretty much a full hour to get to it. On my way there, I was fooled once into thinking there were auroras along an arc from the eastern horizon to overhead as the clouds too on a somewhat auroral shape and alignment with how the auroras typically would look in these conditions. They were just high clouds. By the time it got a little darker, I finally made out the auroral arc in the northeastern sky. The northwestern sky was still filled with twilight.

Initial visibility of the auroral arc over Buck Lake.

I continued onward to my destination of Bower Lake. This lake is in the George Washington State Forest, and there are no houses or human lighting on it. It's a great dark sky spot, and I would not be hearing barking dogs or other human-related noises.

Initial look at the northeastern sky over Bower Lake.

The view more directly to the north as twilight faded.

The auroral arc when twilight finally feded out completely. Note the double arc appearance. That usually means the show will soon be good.

Twilight faded and was finally gone at 11:45 PM. During this time, the auroras remained very steady in an arc across the northern sky. I was wondering whether it would fade into the northern horizon or erupt in a substorm because Bz was trending slowly northward. Solar wind speeds were increasing to around 700 km/s, however, and this favored the likelihood of a substorm.

Surely enough, a brightening occurred after just a few minutes. The brightening usually seems to start from the eastern side of the arc, but this time, it began on the western side. I kept my camera pointed where it was, thinking my higher priority would be for the timelapse I had started. Maybe the auroras would brighten in my camera's view as well. That didn't happen fast enough for me, so I pointed more westward and framed the shot against the trees on the shoreline.

The brightening begins.

I turn my camera northwestward.

The explosion of light as the substorm is in full progress.

Just a few seconds later as the auroras expand a little more southward.

The substorm spread across the remainder of the sky.

Pointing the camera up to get the tops of the auroras (now overhead).

Looking toward the northeastern sky.

Looking back northwest as dimmer auroras spread across more of the sky.

I plopped the camera on top of my car and got this shot.

After driving back out to the state highway, I took this shot.

Back at Buck Lake on my way home.

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