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 Cirrocumulus is one of the three main genus types of high-altitude tropospheric clouds, the other two being cirrus and cirrostratus. They usually occur at an altitude of , however they can occur as low as in the arctic and weather reporting sta ...

altocumulus cloud Altocumulus () is a middle-altitude cloud genus that belongs mainly to the physical category, characterized by globular masses or rolls in layers or patchesthe individual elements being larger and darker than those of cirrocumulus and smaller ...

s. The holes are caused by

supercooled Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. Per the established international definition, supercooling means ''‘cooling a substance be ...

water in the clouds suddenly

evaporating Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humi ...

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 object An unidentified flying object (UFO) is an object or phenomenon seen in the sky but not yet identified or explained. The term was coined when United States Air Force (USAF) investigations into flying saucers found too broad a range of shapes ...

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 Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally occu ...

. When

ice crystals Ice crystals are solid water (known as ice) in crystal structure, symmetrical shapes including hexagonal crystal family, hexagonal columns, hexagonal plates, and dendrite (crystal), dendritic crystals. Ice crystals are responsible for various at ...

do form, a

domino effect A domino effect is the cumulative effect produced when one event sets off a series of similar or related events, a form of chain reaction. The term is an analogy to a falling row of dominoes. It typically refers to a linked sequence of events ...

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

can be formed by passing

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

, 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 Wake or The Wake may refer to: Culture *Wake (ceremony), a ritual which takes place during some funeral ceremonies *Wakes week, an English holiday tradition * Parish Wake, another name of the Welsh ', the fairs held on the local parish's patron s ...

. 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 The Florida panhandle (also known as West Florida and Northwest Florida) is the northwestern part of the U.S. state of Florida. It is a Salient (geography), salient roughly long, bordered by Alabama on the west and north, Georgia (U.S. state ...

that likely were induced by passing aircraft appeared in Corfidi and Brandli (1986). Fallstreak holes are more routinely seen by the higher resolution

satellites A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scientif ...

of today (e.g., see fourth example image in this article). 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 Leeds is a city in West Yorkshire, England. It is the largest settlement in Yorkshire and the administrative centre of the City of Leeds Metropolitan Borough, which is the second most populous district in the United Kingdom. It is built aro ...

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 Ann Arbor is a city in Washtenaw County, Michigan, United States, and its county seat. The 2020 United States census, 2020 census recorded its population to be 123,851, making it the List of municipalities in Michigan, fifth-most populous cit ...

, United States File:Fallstreak, Italy, Borso del Grappa 2019.jpg, A fallstreak hole over

Borso del Grappa Borso del Grappa is a municipality of the Province of Treviso in the Veneto Veneto, officially the Region of Veneto, is one of the 20 regions of Italy, located in the Northeast Italy, north-east of the country. It is the fourth most po ...

, Italy File:Fallstreak Holes over Ho'okipa Maui July 7 2022.jpg, alt=, Fallstreak Holes over

Hoʻokipa Hookipa is a beach on the north shore of Maui, Hawaii, United States, perhaps the most renowned windsurfing site in the world. A combination of large, well-shaped waves breaking across a system of reefs that extend across the bay and consistent ...

beach on Maui, Hawaii, United States

References

External links

Clouds Articles containing video clips Unidentified flying objects {{Cloud types

Origin

Examples

See also

References

External links