Bizarre Natural Phenomena Vol.17 - A Hole In the Clouds (The Fallstreak Hole)

Welcome to another post of the Bizarre Natural Phenomena series! My friends, so far we've been dealing with strange phenomena on earth, but today I'll have you look at the beautiful clouds in the sky. 

(Image source: commons.wikimedia.org)

No, they're neither alien signs, nor HAARP or chemicals trails. This is a magnificently weird cloud formation with a very logical explanation. It is just a skypunch, AKA fallstreak hole (or hole punch cloud, cloud hole and punch hole cloud), a really rare phenomenon.

Why does it happen?

A fallstreak hole happens in the middle or lower levels of a cloud. The water droplets in it need to be in a super-cooled state (below freezing point) even in temperatures as low as  5 degrees Fahrenheit (-15 degrees Celsius). At these temperatures, water is unable to freeze due to lack of ice nucleation (think of it like there is no base for the ice to build up on). This lack of nuclei occurs because the water vapor is very pure (there is very low, if no, concentration of other substances), but below certain temperature levels it can condense into rain or snow. 

(Image source: wikipedia.org)

Although scientists could not explain what triggered this formation, Andy Heymsfield and his colleagues (from the National Center for Atmospheric Research in Boulder, Colorado) published a research in Science 2010, which came to confirm the theory that these wonderful patterns are caused when an aircraft flies through a cloud. Whether it is taking off or touching down, the effect is the same. The team worked with images from a satellite and then experimented on computer simulation, until they ended up to conclude how the mechanism works.

Tell me how!

As we said, within the cloud the water droplets maintain a below-freezing temperature, but are unable to condense to ice. As an aircraft flies through the cloud, it triggers the freezing process like a domino that leaves behind ice particles instead of tiles. This is all well-explained by the Bergeron process (a process of ice formation within clouds). Tiny ice particles within the clouds attract more water vapor and get bigger and bigger. The water droplets then evaporate and become smaller and smaller. As the ice crystals get heavier they start falling to the ground accumulating even more water vapor over their frozen body (Form more information on the process you can check this slideshow).

(Image source:commons.wikimedia.org)

 The flying of the plane lowers the air pressure over its wings and propellers, this leads to an instantaneous further drop in the cloud temperature, so further that the droplets have no other choice but freeze.  As the ice crystals start forming rapidly, they let little amounts of heat escape (do you remember the paradox of latent heat we talked about in the Antarctica Blood Falls post?). This latent heat makes the air around them to expand (its density lowers) and therefore rise, whereas the surrounding air starts to sink a little (because it's cooler and more dense). Water vapor then begins to freeze and sink down as the hole gets bigger and bigger.

The shape of the hole depends on the angle the aircraft flies though it. If the aircraft flies through the cloud in a more shallow angle, the hole will have a different shape. It will form a line known as a canal cloud.

(Image source: flickr.com)

Meteorologist Mark Finan explains how the phenomenon happens, on some pictures of a skypunch over Sacramento.

Should I put a rainbow on it?

In some cases it is possible to see a rainbow within a hole punch cloud. This happens as sunlight gets refracted from the ice particles within the hole. 

(Image by Leesa Willmott, source: nationalgeographic.com)

References

cloudappreciationsociety.org
earthsky.org
crystalinks.com
iflscience.com
wikipedia.org
nationalgeographic.com
mysteriousfacts.com
kidsgeo.com

 Thank you for stopping by and reading today's post! I hope it got your curiosity-radar on to follow me, @ruth-girl, for more fascinating phenomena! 

If nature's weirdness is your thing, you can check some of the previous articles of this series: 

11 - The Toxic Underwater Lake
12 - Underwater Crop Circles
13 - The Spotted Lake
14 - The Huge Crystals Cave
15 - Ice Brinicles
16 - The Clone Forest
17 - The Skypunch
18 - Turquoise Ice Lake

                     

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Until my next post,
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