Fallstreak hole

Large gap in cirrocumulus or altocumulus clouds

Fallstreak hole (Cavum)
Fallstreak hole over Austria
Abbreviation	cav
Genus	Cirrocumulus , Altocumulus , Stratocumulus
Variety	Supplementary feature
Altitude	500-15,000 m (2,000-49,000 ft)
Appearance	Hole in the clouds
Precipitation	Virga

A fallstreak hole (also known as a cavum,^[1] hole punch cloud, punch hole cloud, skypunch, cloud canal or cloud hole) is 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.

Because of their rarity and unusual appearance, fallstreak holes have been mistaken for or attributed to unidentified flying objects.^[2]

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.^[3] 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).^[4] Fallstreak holes are more routinely seen by the higher resolution satellites of today (e.g., see fourth example image in this article).

The articles by Westbrook and Davies (2010)^[5] and Heymsfield et al. (2010)^[6] explain the processes behind the formation of fallstreak holes in greater detail, and show some observations of their microphysics and dynamics. Such clouds are not unique to any one geographic area and have been photographed from many places.

Examples

A fallstreak hole, Leeds, United Kingdom
Elongated fallstreak hole over Bixby
Fallstreak hole over Ann Arbor
A fallstreak hole over Borso del Grappa, Italy
Fallstreak Holes over Ho'okipa beach on Maui, Hawai

References

^ Sutherland, Scott (March 23, 2017). "Cloud Atlas leaps into 21st century with 12 new cloud types". The Weather Network. Pelmorex Media. Retrieved 24 March 2017.
^ "'UFO cloud formation' filmed in Romania (subscription required)". www.telegraph.co.uk. 26 October 2009. Retrieved 13 October 2021.
^ "Cloud Appreciation Society | Fallstreak Holes (February '06)". cloudappreciationsociety.org. 31 July 2006. Retrieved 2017-07-29.
^ Corfidi, Stephen; Brandli, Hank (May 1986). "GOES views aircraft distrails" (PDF). National Weather Digest. 11: 37–39.
^ Westbrook, Chris; Davies, Owain (July 2010). "Observations of a glaciating hole-punch cloud". Weather. 65 (7): 176–180. arXiv:0907.4302. Bibcode:2010Wthr...65..176W. doi:10.1002/wea.504. S2CID 37383288.
^ Heymsfield, Andrew J.; Kennedy, Patrick C.; Massie, Steve; Schmitt, Carl; Wang, Zhien; Haimov, Samuel; Rangno, Art (2010). "Aircraft-Induced Hole Punch and Canal Clouds: Inadvertent Cloud Seeding". Bulletin of the American Meteorological Society. 91 (6): 753–766. Bibcode:2010BAMS...91..753H. doi:10.1175/2009BAMs2905.1.

External links

Wikimedia Commons has media related to Cavum (meteorology).

Cloud genera and selected species, supplementary features, and other airborne hydrometeors - WMO Latin terminology except where indicated

Mesospheric

Extreme-level
80–85 km

Noctilucent (NLC) Polar mesospheric clouds	Noctilucent type I veils Noctilucent type II bands Noctilucent type III billows Noctilucent type IV whirls

Stratospheric

Very high-level
15–30 km

Nacreous polar stratospheric clouds (PSC)	Cirriform nacreous Lenticular nacreous
Nitric acid and water polar stratospheric clouds (PSC)	No differentiated sub-types; tends to resemble cirrostratus

Tropospheric

High-level
3–18 km

Cirrus (Ci)

Species	Cirrus castellanus (Ci cas) Cirrus fibratus (Ci fib) Cirrus floccus (Ci flo) Cirrus spissatus (Ci spa) Cirrus uncinus (Ci unc)
Ci-only varieties	Cirrus intortus (Ci in) Cirrus vertebratus (Ci ve)

Cirrocumulus (Cc)

Species	Cirrocumulus castellanus (Cc cas) Cirrocumulus floccus (Cc flo) Cirrocumulus lenticularis (Cc len) Cirrocumulus stratiformis (Cc str)

Cirrostratus (Cs)

Species	Cirrostratus fibratus (Cs fib) Cirrostratus nebulosus (Cs neb)

High-level-only
mutatus cloud

Mutatus non-height specific (see below)

Medium-level
2–8 km

Altocumulus (Ac)

Species	Altocumulus castellanus (Ac cas) Altocumulus floccus (Ac flo) Altocumulus lenticularis (Ac len) Altocumulus stratiformis (Ac str) Altocumulus volutus (Ac vol)

Altostratus (As)

Altostratus undulatus

Nimbostratus (Ns)
Multi-level

Varieties	Nimbostratus virga (Ns vir)

Low-level
0–2 km

Cumulonimbus (Cb)
Towering vertical

Species	Cumulonimbus calvus (Cb cal) Cumulonimbus capillatus (Cb cap)
Cb-only supplementary features	Cumulonimbus cauda ((cau) Tail cloud) Cumulonimbus incus (inc) Cumulonimbus murus ((mur) Wall cloud)
Cb-only accessories and other	Cumulonimbus flumen ((Cb flu) Beaver tail) Overshooting top Hot tower

Cumulus (Cu)
Variable vertical extent

Species	Fractus Cumulus humilis (Cu hum) Cumulus mediocris (Cu med) (Cumulus congestus (Cu con) (Cumulus castellanus (unofficial alternative name for Cu con)) (ICAO term for Cu con and "Cu cas" is Towering cumulus [Tcu]))
Other	Horseshoe Trade wind cumulus

Stratus (St)

Species	Stratus fractus (St fra) Stratus nebulosus (St neb)
St-only genitus cloud and other	Stratus silvagenitus (St sil) Fog (Fg) Surface level

Stratocumulus (Sc)

Species	Stratocumulus castellanus (Sc cas) Stratocumulus floccus (Sc flo) Stratocumulus lenticularis (Sc len) Stratocumulus stratiformis (Sc str) Stratocumulus Undulatus Stratocumulus volutus (Sc vol)

Low-level-only
supplementary features

Arcus ((arc) Shelf)
Tuba ((tub) Funnel cloud)

Low-level-only
accessory cloud and other

Pileus (pil)
Velum (vel)
Pannus (pan)
Other- Actinoform cloud (Stratocumulus)

Non-height
specific

Varieties	Duplicatus (du) Lacunosus (la) Opacus (op) Perlucidus (pe) Radiatus (ra) Translucidus (tr) Undulatus (un)
Supplementary features	Asperitas (asp) Cavum (cav) Fluctus (flu) Mamma (mam) Praecipitatio (pra) Virga (vir)
Mother clouds and human-made clouds	(Mother cloud)+genitus (e.g. cumulogenitus (cugen) (Mother cloud)+mutatus (e.g. cumulomutatus (cumut) Homogenitus (hogen) Homomutatus (homut)