March 7, 2016 Auroras

Prairie, Pughole, and Wabana Lakes

A coronal hole high speed stream of solar wind interacted with Earth's magnetosphere during the day, igniting the auroras. I attended a ski race earlier in the day, and this was the very first day of the big meltdown of spring. The snow had mostly melted off the ice on the lakes, and things were starting to get slushy. Nonetheless, I decided to go out on a couple lakes once again, knowing that my ability to set up a tripod anywhere on the lake would only last a couple more weeks, at best, given the warm forecast.  On second thought, I almost always go out on the lakes, but in warmer seasons, I am constrained to shoot from boat landings.

I started at Prairie Lake.  If the solar wind conditions during the day had persisted into the evening, I would have been seeing a very dramatic show, as some auroral coronas had been photographed from the northern parts of the United Kingdon, but conditions had calmed considerably since then.  Either way, these were the best conditions of the year, with mostly clear skies, no moon, and a solar wind environment that supported at least moderate auroras.  My first pictures revealed a somewhat moderate display with just a hint of color at the top.

Auroras with a hint of color over Prairie Lake.

I decided to get a little farther away from the city lights of Grand Rapids and headed north on Highway 38. I stopped at Pughole Lake like I often do, walked out on the lake, and pointed the camera north, but I quickly noticed that the Zodiacal light was almost as bright as the auroral arc. The Zodiacal light is caused by space dust in the ecliptic plane (the plane of orbit of the planets) scattering light, and it is apparently most visible on Spring evenings and Fall mornings, after and before twilight, respectively. I pointed west and took a few pictres.

Zodiacal light viewed from Pughole Lake.  24mm shot.

Wider view (16mm, full frame) of the Zodiacal light (extending upward from the bottom center), the Milky Way (across the top), and the glow from the southernmost extent of the auroras (lower right side).  On the upper right is a passing satellite.

The light cast from the house and yard light in the lower right picture was illuminating the lake surface more than I wanted, so I decided to head to a darker location. I had been to Wabana Lake three days earlier, so I decided it would be a good place to go again tonight.  When I got to the lake, I saw that the auroral oval had brightened up a bit, so I though it would be a good idea to hurry up and get out there.  Before I could get to the end of the point where I had shot three nights ago, the substorm started.

An auroral substorm erupts through the trees on Wabana Lake.

I continued out to the end of the point and started shooting a time lapse. I ran back to the car and got the other camera to shoot some wider angle stills.

I got to the end of the point to shoot the continuation of the substorm.

The structure faded a bit, the oval got a bit farther south (closer), and more structure showed up at the horizon.

During this particular phase of the display, a fellow Great Lakes Aurora Hunters member was shooting near his home in Gillam, Manitoba. He posted some fantastic images on the Facebook group page, and I decided to look back to see if I might have been shooting at the same time because I certainly was looking in his direction. I found the image I thought most corresponded to one that he posted on Facebook. I'll never know for sure, but the following image shows an arc of auroras that probably lies over Gillam. Auroras whose bases are just a degree or two above my visible horizon, if that base is 100 km above ground as is typical, would be about 600 miles north of me, which would put them near Gillam. Anyway, it's interesting to think about. The auroras can be seen from pretty far away!

Gillam, Manitoba has some auroras overhead and to the south just at this moment.

Anyway, I continued to shoot, and finally called it quits a little after 11:00 PM. That's actually really early for an aurora shoot. The ski race earlier in the day must have made me REALLY tired. I found it really difficult to stay awake for the 25-minute drive home. I pulled into the garage, put the car in park, and proceeded to fall asleep in my car! I woke up about an hour later and went to bed.

The display became a little more diffuse, and some reds appeared.

Anyway, back to that comparison from three nights ago. I could NOT see any evidence of International Falls city lights on the horizon this time. While I had some time, I decided to line up the camera so I could shoot nearly an identical image as three nights ago and see how the illumination along the horizon changed. I made an animated gif of the two images. You can see that an addition of auroral glow, even if most of it is above the horizon, certainly adds a bit of light at the horizon, obscuring any city lights. At the same time, it looks like there is less total light at the horizon, so the city lights must not have been showing up as well. The stars actually look a bit sharper on the aurora-free image as well. There must have been something about the atmospheric transmissivity that allowed more light through three nights ago than tonight. One thing that appears to be the case is that the relative humidity in the upper troposphere was higher, as evidenced by the presence of a few cirrus clouds and contrails. Cirrus clouds would dim the stars and auroras a bit, but I would think this would also allow reflection of the city lights off the cloud bases. I did not see that. Thus, the appearance of distant city light on some nights and not on others remains a mystery for now. I'm now recalling a couple nights of shooting on Lake of the Woods in January 2012 and January 2014. One night had a relatively high humidity and temperatures in the single digits below zero Fahrenheit, while the other had less moisture and temperatures reaching down to -40 degrees Fahrenheit. On the drier night, I could see the lights of Kenora, about 60 miles away, but on the warmer, higher humidity night, I could not. With the exposure settings the same, the RGB values on a point in the city light glow in the image from three nights ago is (101,73,43) versus (82,74,44) on the image from tonight. There is less red light present.

A comparison of the light transmissivity on March 7 and March 4 (UTC dates).  The images are unaltered from the originals in the camera, except to do an exposure correction to compensate for the difference in shutter speed (10s versus 13s).

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