A fallstreak hole (also known as a cavum, 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 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 . Like lower-altitude cumuliform and stratocumuliform clouds, cirrocumulus si ...

altocumulus cloud Altocumulus (From Latin ''Altus'', "high", ''cumulus'', "heaped") is a middle-altitude cloud genus that belongs mainly to the ''stratocumuliform'' physical category characterized by globular masses or rolls in layers or patches, the individual ele ...

s. 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 object An unidentified flying object (UFO), more recently renamed by US officials as a UAP (unidentified aerial phenomenon), is any perceived aerial phenomenon that cannot be immediately identified or explained. On investigation, most UFOs are id ...

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 An ice nucleus, also known as an ice nucleating particle (INP), is a particle which acts as the nucleus for the formation of an ice crystal in the atmosphere. Ice Nucleation Mechanisms There are a number of mechanisms of ice nucleation in the atmo ...

. When

ice crystals Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. Formation The hugely symmetric shapes are due to depositional growth, na ...

do form, a

domino effect A domino effect or chain reaction is the cumulative effect generated when a particular event triggers a chain of similar events. This term is best known as a mechanical effect and is used as an analogy to a falling row of dominoes. It typically ...

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 is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...

, 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 West Florida and Northwest Florida) is the northwestern part of the U.S. state of Florida; it is a Salient (geography), salient roughly long and wide, lying between Alabama on the north and the west, Georgia (U. ...

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 artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...

of today (e.g., see fourth example image in this article). The articles by 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. Such clouds are not unique to any one geographic area and have been photographed from many places.

Examples

File:Fallstreak Hole over Leeds in the UK taken January 2022.jpg, A fallstreak hole, Leeds, United Kingdom, January 18th 2022 File:Fallstreak hole elongated 2020 02 21 BA home Image 4963.png, Elongated fallstreak hole over Bixby, Feb 21, 2020 at 1627 CST File:FallstreakHole AnnArbor MI Nov2016.jpg, Fallstreak hole over

Ann Arbor Anne, alternatively spelled Ann, is a form of the Latin female given name Anna (name), Anna. This in turn is a representation of the Hebrew Hannah (given name), Hannah, which means 'favour' or 'grace'. Related names include Annie (given name), ...

, Nov 14, 2016 File:Texas tmo 2007029 lrg.jpg, Satellite image of canals and fallstreak holes over east Texas and Louisiana, Jan 2007 File:Naple's fallstreak hole.jpg, Fallstreak Hole over Naples, Italy, December 26, 2018 File:OKC-Fallstreak.jpg, Fallstreak Hole over Oklahoma City, Oklahoma, January 2010 File:Fallstreak, Italy, Borso del Grappa 2019.jpg, Fallstreak, Italy, Borso del Grappa, March 19, 2019 File:Virga MX02.jpg, A fall streak hole in

Northern Mexico Northern Mexico ( es, el Norte de México ), commonly referred as , is an informal term for the northern cultural and geographical area in Mexico. Depending on the source, it contains some or all of the states of Baja California, Baja California ...

, March 23, 2021 File:Fallstreak Holes over Ho'okipa Maui July 7 2022.jpg, alt=, Fallstreak Holes over Ho'okipa beach on Maui, Hawaii July 7, 2022

References

External links

Clouds Articles containing video clips Unidentified flying objects {{climate-stub

Origin

Examples

See also

References

External links