August 16, 2013 Auroras
Grand Rapids, MN
These auroras were from a high speed solar wind stream. At sunset, I thought it would be a good idea to head over to the north side of town and see if I could see the auroral oval. I could not yet see it from home. When I arrived at McKinney Lake, a substorm of brighter auroras was already starting. I took pictures at this location for about 20 minutes until this substorm passed. The roar of the stock car races nearby was nearly deafening, so I wanted to move.
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| Substorm begins over McKinney Lake in Grand Rapids. |
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| Bright green intensifies, and purple appears above. |
I then moved over to one of my favorite spots: Trout Lake. The magnetic field was still looking pretty active, so I expected more substorms, but none came. Instead, the green glow persisted to the north while a very narrow band of auroras developed in an arc from the west, overhead, to the eastern horizon. I've heard these referred to as proton arcs, although I'm still not clear about what makes them different from regular auroras, if there's any difference at all. I do know that their color seems a bit more subdued, and they have more of a gray-ish appearance, although it occasionally goes green.
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| I've often heard these features referred to as proton arcs, but what I see is a very narrow aurora well south of the main band. |
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| Here's a fisheye view of the arc. |
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| Solar Dynamics Observatory image of the coronal hole (it's the large dark spot). |
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| Solar wind data showing Bz to -8 (red, top panel) and speeds approaching 800 km/s (fourth panel). |
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