December 12, 2025 Auroras

Grand Rapids, MN

The solar wind conditions were, once again, unsettled. This time, the Bz was not as far south, so auroras were closer to the horizon, and we only had Kp4 type geomagnetic conditions.  This was still good enough for some bright auroras close to the horizon.

I started out early in the evening after work, heading up to Prairie Lake, to see what was out there. I was pleasantly suprised to see not only the main auroral band along the northern horizon, but also an intermittent band of proton auroras higher in the sky. Given that these are rather fleeting and can disappear quickly, I grabbed my camera and took a few shots. Indeed, they were gone in a couple minutes, leaving just the primary arc of auroras on the northern horizon.

I watched for a bit, and when things settled down, I decided to go home and attend to a few chores (these mostly ended up being writing up last night's aurora account). Bz remained south, and I figured there would be another decent show. I went out again around 10:30 and found a steady auroral arc. This is usually the precursor to a substorm. All I would have to do is wait for a bit, and a more brilliant, active display would start. This took only about 15 minutes after I initially started taking pictures.

As the show was continuing, the temptation to drive up to Wabana Lake overwhelmed me. Ideally, this would have been the best place to shoot this show because of its proximity to the horizon, but I was worried the show might start before I got there (I was correct-- it did start before I would have gotten there). However, now that I knew I would not miss the show, and thinking of the small chance that another one could quickly follow (this happens only in about one out of five or ten substorms), I drove up to Wabana and walked out onto the lake. The second substorm did not follow, but I enjoyed being out on this lake for what was probably my earliest outing at this location in the winter season. Usually, I'm not out there until at least January because December auroras are the rarest in Minnesota. This December, I've seen them three times already-- that's the most of any December since I've kept track.

Two types of auroras are present here: common (electron-precipitation) auroras on the right near the horizon, with pillars, and less common (proton) auroras in two patches-- to the left and closer to the center of the picture.

The proton auroras disappeared, leaving the primary auroral arc near the horizon.

Later in the evening, a steady auroral arc is in place, prior to a substorm containing more active auroras.

The substorm begins. The auroras brighten and move along the auroral arc.

The substorm is in full progress.

The very late stage of the substorm, viewed from Wabana Lake.

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