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Leaping sundogs
November 17, 2011 9:54 AM   Subscribe

Leaping Sundogs "...that little wisp suddenly snaps into a new shape, as if someone had stopped the video, waited for the cloud to change, then started up the video again." More here.
posted by dhruva (11 comments total) 15 users marked this as a favorite

 
woah - very cool
posted by zeoslap at 10:03 AM on November 17, 2011


It was ruined for me with the explanation. Its so much cooler to think its magic!
posted by sfts2 at 10:04 AM on November 17, 2011


Just the New World Order playing with the weather machine again. Nothing to see here.
posted by Curious Artificer at 10:09 AM on November 17, 2011 [1 favorite]


It was ruined for me with the explanation. Its so much cooler to think its magic!

Boooooooooo!
posted by anazgnos at 10:13 AM on November 17, 2011 [7 favorites]


Its so much cooler to think its magic!

I think flying ice crystals aligning with electric fields generated by clouds is pretty magical.
posted by DU at 10:23 AM on November 17, 2011 [10 favorites]


I think flying ice crystals aligning with electric fields generated by clouds is pretty magical.

That's an awfully fancy way to describe the Care Bear Cloud Car.
posted by Fizz at 10:27 AM on November 17, 2011


I'm so glad that whoever took the video didn't narrate it. It was lovely to be quietly immersed in that moment.
posted by EvaDestruction at 10:46 AM on November 17, 2011 [3 favorites]


I'm so glad that whoever took the video didn't narrate it.
Me too, I'm sure it would be autotuned and set to music and have all the wonder sucked out of it.
posted by phirleh at 11:27 AM on November 17, 2011


It surprised me that Bad Astronomer initially thought the cloud was actually changing shape...or, at least, that's how I read his initial speculations. Re-reading them, he uses the word "appear", which makes it more ambiguous.

To my eye, it's necessarily an optical effect because there's no way that the ice crystals could move those distances that quickly.

To be clear to those who didn't read the explanation or entirely follow it: what's happening is that the ice crystals in the cloud act like individual lenses/prisms and collectively as a compound lens/mirror directing the light from the Sun. How the individual crystals are aligned determines how the Sun's light is directed, and can create anything from a duplicate image of the Sun, to halos, to more complex stuff. What we see in the video is (some of) the Sun's light (which has passed through the mass of ice crystals in the atmosphere) being directed toward the observer on the ground with the video camera—that region of the sky looked differently to other observers in different places on the ground.

The image changes as the ice crystals suddenly change their orientation (not relative positions), which changes how they collectively act as a compound lens/mirror. The crystals rapidly change their orientation because their individual surfaces accumulate an electric potential, which then results in their individual alignment in accordance to a magnetic field around them (which itself results from electric currents running through the clouds and atmosphere). That magnetic field can suddenly change when there is, for example, a massive discharge of accumulated electric potential from one area to another—that's a current flow, creating a strong transient magnetic field, and will often be seen as lightning. So the image generated by the ice crystals (to an observer at a particular position) will be stable for a short while, then suddenly change, then be stable for awhile, then suddenly change. This will continue for as long as that region of the atmosphere (because of the ice crystals it contains, mostly) is accumulating and then discharging electric potential.

The imagery generated is dependent upon a specific set of conditions, including the Sun's relative position and probably the size of the ice crystals, and likely numerous other variables. Likely it's the case that these sorts of optical effects are more common than they are observed, because they will be specific to observation at only particular points on the ground. Most will be unobserved, assuming the effect is being generated in the first place.
posted by Ivan Fyodorovich at 12:02 PM on November 17, 2011


Some of the other related videos have strange cloud stuff going on, too.

Mattress-sized cloud gets stopped by chain-link fence

Jellyfish Vortex Cloud
posted by not_on_display at 12:08 PM on November 17, 2011


You can simulate some of this yourself. More here.
posted by jet_silver at 6:30 PM on November 17, 2011


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