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 s ...
or
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 ide ...
s.
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
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, n ...
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
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, n ...
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 engine ...
, 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 (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, 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
See also
*
List of cloud types
The list of cloud types groups all genera as ''high'' (cirro-, cirrus), ''middle'' (alto-), ''multi-level'' (nimbo-, cumulo-, cumulus), and ''low'' (strato-, stratus). These groupings are determined by the altitude level or levels in the troposphe ...
*
Circumhorizontal arc
A circumhorizontal arc is an optical phenomenon that belongs to the family of ice halos formed by the refraction of sunlight or moonlight in plate-shaped ice crystals suspended in the atmosphere, typically in cirrus or cirrostratus clouds. In ...
*
Cloud iridescence
Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. It is a type of photom ...
*
Distrails
*
Virga
In meteorology, a virga, also called a dry storm, is an observable streak or shaft of precipitation falling from a cloud that evaporates or sublimates before reaching the ground. A shaft of precipitation that does not evaporate before rea ...
References
External links
Clouds
Articles containing video clips
Unidentified flying objects
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