Traditionally I think of the aurora being generated from a sun event. Often C-class flares, M-class flares, and X-class flares (the largest) hurtle plasma towards at the earth resulting in brilliant auroras. I have dug into the science of auroras during previous posts, and wrote about some of the science of the auroral colors and why the aurora can go from a nice show to a great show. However, last nights aurora event was generated by a “Coronal Hole” in the sun. That term was new to me, and although it sounds like a headline from an end of days article, it’s really not that bad!
Coronal holes are a simple concept. The sun normally has a stable magnetic field that controls solar winds and energy from the sun. During a coronal hole event, magnetic field lines extend far away from the sun and allow high speed solar winds to escape. Solar wind speeds may exceed 10,000,000 km/hr! Translating that to terms I understand more, solar winds can travel at 500 miles/second. That’s a quick commute to work, or in this case the earth! If the coronal hole is ‘geo-effective’ it means that those solar winds are headed towards our planet. These events can lead to a lot of high energy resulting in red and multicolored auroras even during times of low solar activity. (http://www.spaceweatherlive.com/en/help/what-is-a-coronal-hole, http://www.exploratorium.edu/spaceweather/holes.html)
Last night’s show was stopped at 10:30 due to clouds over Fairbanks. From 8:30 – 10:30 it remained subtle, but beautiful. The high energy from the coronal hole produced a quickly changing, but not well defined red aurora. I hope you enjoy!