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What Punched a Hole in these Clouds?

Chris Dolce | TWC
Published: January 25, 2013

Hole-Punch Clouds

Hole-Punch Clouds

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From Gibson, La. in December 2008. iWitness Weather contributor jamiecg.

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  • Hole-Punch Clouds - Satellite View
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It looks as if someone perfectly punched out holes in the sky of each cloud photo above, but obviously we know they were not made by hand. However, you could say that humans do play a role in their development.

(PHOTOS: 10 Spectacular Clouds)

These rare cloud formations, called "hole-punch clouds", develop in altocumulus cloud layers and are often the result of airplanes passing through the layer of clouds.

So, how does this happen?

The altocumulus cloud layer is composed of small water droplets that are below freezing called supercooled water droplets. If ice crystals can form in the layer of supercooled droplets, they will grow rapidly and shrink or possibly evaporate the droplets completely. 

Studies, including this one by Andrew Heymsfield and collaborators, have shown that aircraft passing through these cloud layers can trigger the formation of the heavier ice crystals, which fall to earth and then leave the circular void in the blanket of clouds. They concluded that aircraft propellers and wings cause the formation of those initial ice crystals. There are zones of locally low pressure along the wing and propeller tips which allow the air to expand and cool well below the original temperature of the cloud layer, forming ice crystals.

The ice crystals are the wispy-looking clouds in the middle of the holes in each photo above.

Our Severe Weather Expert Dr. Greg Forbes says that hole-punch clouds can also form when a few ice crystals "spontaneously" form within the supercooled cloud and then "take over".

Dr. Forbes has a much more detailed look at how these clouds form at this link.


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