February 3, 2017 Auroras
Grand Rapids, Minnesota
For the second night in a row, the solar wind conditions were favorable for some auroras. The north-south component of the magnetic field (Bz) was negative, but not by very much. It was dipping only as low as -4 nT, but with the solar wind speed near 700 km/s, that was enough to brighten the night sky with green. I had done some cross-country ski trail grooming earlier in the evening, and when I checked for auroras during the grooming and just afteward, I did not really see anything, but the solar wind data looked good enough, so I waited. Indeed, the auroras appeared.
At first, they were a faint glow along the far northern horizon, but with time, they developed into a band about four degrees above the horizon. I thought we might get a nicely structured substorm with dancing columns and curtains, but that didn't really happen. Instead, the main band slowly broke up into the "blob" style auroras that pulsed on a time scale of several seconds.
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| Blob-style auroras over Prairie Lake. |