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Fallstreak hole
Large gap in cirrocumulus or altocumulus clouds
Large gap in cirrocumulus or altocumulus clouds
| Field | Value |
|---|---|
| name | Fallstreak hole (Cavum) |
| image location | HolePunchCloud.jpg |
| image name | Fallstreak hole over Austria |
| abbreviation | cav |
| genus | Cirrocumulus, altocumulus, stratocumulus |
| variety | Supplementary feature |
| altitude_m | 500–15,000 |
| altitude_ft | 2,000–49,000 |
| level | High or medium |
| appearance | Hole in the clouds |
| precipitation | Virga |
A fallstreak holealso known as a cavum, hole punch cloud, punch hole cloud, skypunch, cloud canal, or cloud holeis a large gap, usually circular or elliptical, that can appear in cirrocumulus or altocumulus clouds. The holes are caused by supercooled water in the clouds suddenly evaporating or freezing, and may be triggered by passing aircraft. Such clouds are not unique to any one geographic area and have been photographed from many places.
Due to their rarity and unusual appearance, fallstreak holes have been mistaken for or attributed to unidentified flying objects.
Origin
Such holes are formed when the water temperature in the clouds is below freezing, but the water, in a supercooled state, has not frozen yet due to the lack of ice nucleation. When ice crystals do form, a domino effect is set off due to the Wegener-Bergeron-Findeisen process, causing the water droplets around the crystals to evaporate; this leaves a large, often circular, hole in the cloud. It is thought that the introduction of large numbers of tiny ice crystals into the cloud layer sets off this domino effect of fusion which creates the hole.
The ice crystals can be formed by passing aircraft, which often have a large reduction in pressure behind the wing-tip or propeller-tips. This cools the air very quickly, and can produce a ribbon of ice crystals trailing in the aircraft's wake. These ice crystals find themselves surrounded by droplets, and grow quickly by the Bergeron process, causing the droplets to evaporate and creating a hole with brush-like streaks of ice crystals below it. An early satellite documentation of elongated fallstreak holes over the Florida Panhandle that likely were induced by passing aircraft appeared in Corfidi and Brandli (1986). Fallstreak holes are more routinely seen by the higher resolution satellites of today.
Westbrook and Davies (2010) and Heymsfield et al. (2010) explain the processes behind the formation of fallstreak holes in greater detail, and show some observations of their microphysics and dynamics.
Examples
File:Fallstreak Hole over Leeds in the UK taken January 2022.jpg|A fallstreak hole, Leeds, United Kingdom File:Fallstreak hole elongated 2020 02 21 BA home Image 4963.png|Elongated fallstreak hole over Bixby, United States File:FallstreakHole AnnArbor MI Nov2016.jpg|Fallstreak hole over Ann Arbor, United States File:Fallstreak, Italy, Borso del Grappa 2019.jpg|A fallstreak hole over Borso del Grappa, Italy File:Fallstreak Holes over Ho'okipa Maui July 7 2022.jpg|alt=|Fallstreak Holes over Hoʻokipa beach on Maui, Hawaii, United States
References
References
- (March 23, 2017). "Cloud Atlas joins the digital age while adding a dozen new cloud types". The Weather Network.
- (2009-10-26). "'UFO cloud formation' filmed in Romania (subscription required)". [[The Daily Telegraph]].
- (31 July 2006). "Cloud Appreciation Society {{!}} Fallstreak Holes (February '06)".
- Corfidi, Stephen. (May 1986). "GOES views aircraft distrails". National Weather Digest.
- Westbrook, Chris. (July 2010). "Observations of a glaciating hole-punch cloud". Weather.
- (2010). "Aircraft-Induced Hole Punch and Canal Clouds: Inadvertent Cloud Seeding". Bulletin of the American Meteorological Society.
This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.
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