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 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.
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 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
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, 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
*
Circumhorizontal arc
*
Cloud iridescence
*
Distrails
*
Virga
References
External links
Clouds
Articles containing video clips
Unidentified flying objects
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