Editing Diamond dust

{{Short description|Ground-level cloud of ice crystals}}
{{Other uses}}
{{Weather}}

'''Diamond dust''' is a ground-level [[cloud]] composed of tiny [[ice]] crystals. This [[list of meteorological phenomena|meteorological phenomenon]] is also referred to simply as ''[[ice crystals]]'' and is reported in the [[METAR]] code as '''IC'''. Diamond dust generally forms under otherwise clear or nearly clear skies, so it is sometimes referred to as clear-sky [[Precipitation (meteorology)|precipitation]]. Diamond dust is most commonly observed in [[Antarctica]] and the [[Arctic]], but can occur anywhere with a temperature well below freezing. In the [[polar regions of Earth]], diamond dust may persist for several days without interruption.

==Characteristics==
[[File:Diamond Dust - Inari 2013.ogv|thumb|Falling diamond dust (Inari, Finland)]]
Diamond dust is similar to [[fog]] in that it is a cloud based at the surface; however, it differs from fog in two main ways. Generally fog refers to a cloud composed of liquid water (the term [[ice fog]] usually refers to a fog that formed as liquid water and then froze, and frequently seems to occur in valleys with airborne pollution such as [[Fairbanks, Alaska|Fairbanks]], [[Alaska]], while diamond dust forms directly as ice). Also, fog is a dense-enough cloud to significantly reduce visibility, while diamond dust is usually very thin and may not have any effect on visibility (there are far fewer crystals in a volume of air than there are droplets in the same volume with fog). Because mist is often classified to be more transparent than fog, diamond dust has often been referred to as '''ice mist'''. However, diamond dust still can often reduce the visibility, in some cases to under {{convert|600|m|abbr=on}}.

The depth of the diamond dust layer can vary substantially from as little as {{convert|20|to|30|m|abbr=on}} to {{convert|300|m}}. Because diamond dust does not always reduce visibility it is often first noticed by the brief flashes caused when the tiny crystals, tumbling through the air, reflect sunlight to the eye. This glittering effect gives the phenomenon its name since it looks like many tiny diamonds are flashing in the air.

<gallery caption="serial photos of Diamond Dust" widths="180px" heights="240px" perrow="2">
File:050207diamond dust1 Tsukuba Japan.png|Diamond dust briefly observed at Tsukuba, Japan. These are serial photos out of a movie; note differences in crystal locations.
File:050207diamond dust2 Tsukuba Japan.png|Temperature was -2&nbsp;°C, relative humidity was almost 100%. These photos captured only the glittering particles.
</gallery>

==Formation==
[[Image:Sun halo optical phenomenon edit.jpg|thumb|upright|Halo display at the South Pole (1980), featuring a [[parhelion]], [[22° halo]], [[parhelic circle]], [[upper tangent arc]] and [[Parry arc]]. Diamond dust is visible as point-like reflections of individual crystals close to the camera.]][[File:Losvåttån Løkken Verk 2.jpg|thumb|Diamond dust in [[Løkken Verk]], Norway.]]
These ice crystals usually form when a [[Inversion (meteorology)|temperature inversion]] is present at the surface and the warmer air above the ground mixes with the colder air near the surface.<ref name="gloss">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|author=Glossary of Meteorology|date=June 2000|title=Diamond Dust|publisher=[[American Meteorological Society]]|access-date=2010-01-21|url-status=dead|archive-url=https://web.archive.org/web/20090403084329/http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|archive-date=2009-04-03}}</ref> Since warmer air frequently contains more [[water vapor]] than colder air, this mixing will usually also transport water vapor into the air near the surface, causing the [[relative humidity]] of the near-surface air to increase. If the relative humidity increase near the surface is large enough then ice crystals may form.

To form diamond dust the temperature must be below the [[Melting point|freezing point]] of water, {{convert|0|C|abbr=on}}, or the ice cannot form or would melt. However, diamond dust is not often observed at temperatures near {{convert|0|C|abbr=on}}. At temperatures between {{convert|0|C|abbr=on}} and about {{convert|-39|C|abbr=on}} increasing the relative humidity can cause either fog or diamond dust. This is because very small droplets of water can remain liquid well below the freezing point, a state known as [[Supercooling|supercooled]] water. In areas with a lot of small particles in the air, from human pollution or natural sources like dust, the water droplets are likely to be able to freeze at a temperature around {{convert|-10|C|abbr=on}}, but in very clean areas, where there are no particles ([[Ice nucleus|ice nuclei]]) to help the droplets freeze, they can remain liquid to {{convert|-39|C|abbr=on}}, at which point even very tiny, pure water droplets will freeze. In the interior of Antarctica diamond dust is fairly common at temperatures below about {{convert|-25|C|abbr=on}}.

Artificial diamond dust can form from snow machines which blow ice crystals into the air. These are found at ski resorts. Diamond dust may also be observed immediately downwind from manufacturing facilities or chilled water plants that produce steam.

==Optical properties==

Diamond dust is often associated with [[Halo (optical phenomenon)|halo]]s, such as [[sun dogs]], [[light pillar]]s, etc. Like the ice crystals in [[cirrus cloud|cirrus]] or [[cirrostratus cloud]]s, diamond dust crystals form directly as simple hexagonal ice crystals — as opposed to freezing drops —<ref>{{cite journal|publisher=[[California Institute of Technology]]|url=http://www.its.caltech.edu/~atomic/publist/engsci2.pdf|page=12|year=2001|author=Kenneth G. Libbrecht|title=Morphogenesis on Ice: The Physics of Snow Crystals|journal=Engineering & Science|number=1|access-date=2001-01-21}}</ref> and generally form slowly. This combination results in crystals with well defined shapes - usually either hexagonal plates or columns - which, like a prism, can [[reflection (physics)|reflect]] and/or [[Refraction|refract]] light in specific directions.

==Climatology==
While diamond dust can be seen in any area of the world that has cold winters, it is most frequent in the interior of Antarctica, where it is common year-round. Schwerdtfeger (1970) shows that diamond dust was observed on average 316 days a year at [[Plateau Station]] in Antarctica, and Radok and Lile (1977) estimate that over 70% of the precipitation that fell at Plateau Station in 1967 fell in the form of diamond dust. Once melted, the total precipitation for the year was only {{convert|25|mm|abbr=on}}.

==Weather reporting and interference==
Diamond dust may sometimes cause a problem for [[automated airport weather station]]s. The [[ceilometer]] and visibility sensor do not always correctly interpret the falling diamond dust and report the visibility and ceiling as zero (overcast skies). However, a human observer would correctly notice clear skies and unrestricted visibility. The METAR identifier for diamond dust within international hourly weather reports is IC.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar+taf/sametara.htm |archive-url=https://web.archive.org/web/20180905214814/https://www.alaska.faa.gov/fai/afss/metar+taf/sametara.htm |url-status=dead |archive-date=2018-09-05 |title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]] via the Internet Wayback Machine|access-date=2009-08-29|date=2007-04-10 }}</ref>

== See also ==
* [[Crepuscular rays]]
* [[Light beam]]
* [[False sunrise]]
* [[False sunset]]

==References==
{{reflist}}

===Further reading===
*{{cite book|author=Greenler, R.|year=1999|title=Rainbows, Halos, and Glories|publisher=Peanut Butter Publishing|location=Milwaukee|pages=195 pp|isbn=0-89716-926-3}} &mdash; An excellent reference for optical phenomena including photos of displays in Antarctica caused by diamond dust.
*{{cite book|author=Schwerdtfeger, W.|year=1970|chapter=The climate of the Antarctic|editor=S. Orvig|title=Climates of the Polar Regions|volume=14|series=World Survey of Climatology|pages=253–355|publisher=[[Elsevier]]|isbn=0-444-40828-2}}
*{{cite book|author=Radok, U. and R.C. Lile|year=1977|chapter=A year of snow accumulation at Plateau Station|editor=J.A. Businger|editor-link=Joost Businger|title=Meteorological Studies at Plateau Station, Antarctica|volume=25|series=Antarctic Research Series|pages=17–26|publisher=[[American Geophysical Union]]|isbn=0-87590-125-5}}
*{{cite book|title=Manual of Surface Weather Observations (MANOBS)|date=2 December 2021 |edition=8th|publisher=Meteorological Service of Canada|url=https://www.canada.ca/en/environment-climate-change/services/weather-manuals-documentation/manobs-surface-observations.html}}
*[https://web.archive.org/web/20090226192401/http://tanken-n.com/event.php?no=33 Photo of artificial Diamond Dust] {{in lang|ja}}

==External links==
*[https://www.youtube.com/watch?v=Aq-BsY_0oz0 A remarkable video filmed in Hokkaido, Japan. 1min 22sec HQ] {{in lang|ja}}
*[https://www.youtube.com/watch?v=CdVHoFK3Lp0 Longer version of the above video. 5min 10sec HD] {{in lang|ja}}
Note that images are different from the naked eye in that they capture out-of-focus crystals which are shown as large, blurred objects.

{{ice}}
[https://www.dseodisha.com/the-science-behind-diamond-dust/ The Science Behind Diamond Dust: How It Reflects Solar Radiation]

[[Category:Psychrometrics]]
[[Category:Precipitation]]
[[Category:Water ice]]
[[Category:Snow or ice weather phenomena]]
[[Category:Atmospheric optical phenomena]]
[[Category:Articles containing video clips]]

[[sv:Diamantstoft]]