Anatomy of a Geomagnetic Storm - What made that great Aurora?

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Shawn Malone took this photo of Aurora on October 24, 2011 in Marquette Michigan.

Saturday, October 22, 2011, started like most any other day, lots of activity of varying size and shape was occurring on the Sun. Most people looking at the Sun that day remember the spectacular lightbulb shaped CME that occurred from just behind the Northwest limb.

Here is the eruption and flare.

and the resulting CME.

But it turns out the really interesting event originated from a filament on the solar disk just to the left of the more spectacular eruption. Just before the eruption that produced the lightbulb CME and filament eruption almost went unnoticed. The only real sign was after the filament lifted off. The magnetic field that tied the filament down, like a series of ropes tying down a long skinny balloon, was ripped away from the surface spreading outward. Where they were connected to the surface and pull away they left 2 expanding ribbons.

Once the filament left the solar surface it formed an irregular shaped CME directed toward Earth. It can been seen here in SOHO/LASCO and it occurred just before the lightbulb CME.
http://www.youtube.com/watch?v=Z6z9Kf3KkQg
It turns out that the filament contained a knot of magnetic field that was southward directed. This partially countered the northward magnetic field of Earth. This combined with the CMEs strong compression of the magnetosphere created a strong geomagnetic storm that generated aurora to low magnetic latitudes. This is why aurora were seen as far south as Alabama, USA. Aurora were seen around the world including in over 30 US states. Here is a great video illustrating what happened by Dr. Keith Strong of NASA’s Goddard Space Flight Center.

Many observers saw a red aurora. Red auroras are rarer. There is a nice discussion of red aurora by Carla Helfferich.

Here are just a few of the many Aurora photos taken by observers.

: Shawn Malone: “WOWOWOWOW! Incredible! Best northern lights I’ve seen since 2004! Northern Lights in every direction, photographed most of the time facing south! Beautiful coronas, many reds!”

: Geir Øye: “These are the strongest and most beautiful auroras I’ve ever seen. I can only imagine what the display must have been further north. Considering these images are taken at ‘only’ 62nd lat N. Here are a few vistas taken from 00.41 – 01.34 local time on August 25, 2011. (more images will be placed on my www – site later today.) Photo details: Canon 500D, 15 mm fisheye lens, tripod. http://www.skyoye.com/aurora2011.html”

: Peter Henshaw: “I took this last night near Moodys, Oklahoma about 8:30 p.m. CST facing north. Moodys is located north of Tahlequah, OK, which should appear on most maps. I was about 27 miles north of Tahlequah using a cigarette pack and a car as my tripod. It’s a bit blurry. I used the Canon T3i with the kit lens at 18mm. 20s exposure. The sky was darker than the image on the camera. I used auto levels on the camera as I it was dark and I couldn’t tell the true color, just knew the sky wasn’t black.”

: Imagery was processed at Fleet Numerical Meteorology and Oceanography Center (FNMOC) in Monterey CA, USA. Paul McCrone: “These are nighttime visual and multispectral images of the Aurora Borealis from the DMSP satellite F18 on Oct 25, 2011, 0140 GMT.”

: Frank Olsen: “This image was taken just outside Tromsø, Norway around midnight UTC, 01 am local time. It was a spectacular sight! I’ve never before seen red and purple auroras with the naked eye.”