ice crystal

File:Hexagonal Ice Crystals.svg

 At ambient temperature and pressure, water molecules have a V shape. The two hydrogen atoms bond to the oxygen atom at a 105° angle.{{Cite web |last=Puiu |first=Tibi |date=2015-03-27 |title=Sandwiching water between graphene makes square ice crystals at room temperature |url=https://www.zmescience.com/science/chemistry/graphene-square-ice-0534534/ |access-date=2023-03-30 |website=ZME Science |language=en-US}} Ice crystals have a hexagonal crystal lattice, meaning the water molecules arrange themselves into layered hexagons upon freezing.

Slower crystal growth from colder and drier atmospheres produces more hexagonal symmetry. Depending on environmental temperature and humidity, ice crystals can develop from the initial hexagonal prism into many symmetric shapes.{{Cite book |last=Visconti |first=Guido |url=https://www.worldcat.org/oclc/46320998 |title=Fundamentals of physics and chemistry of the atmosphere |date=2001 |publisher=Springer |isbn=3-540-67420-9 |location=Berlin |oclc=46320998}} Possible shapes for ice crystals are columns, needles, plates and dendrites. Mixed patterns are also possible. The symmetric shapes are due to depositional growth, which is when ice forms directly from water vapor in the atmosphere.{{Cite web |title=Sublimation and deposition - Energy Education |url=https://energyeducation.ca/encyclopedia/Sublimation_and_deposition#:~:text=An%20example%20of%20deposition%20is,as%20the%20formation%20of%20frost. |access-date=2023-04-10 |website=energyeducation.ca}} Small spaces in atmospheric particles can also collect water, freeze, and form ice crystals.{{Cite web |last=Utah |first=University of |title=We've been thinking of how ice forms in cirrus clouds all wrong |url=https://phys.org/news/2019-04-weve-ice-cirrus-clouds-wrong.html |access-date=2023-03-30 |website=phys.org |language=en}}{{Cite web |title=How ice crystals form in clouds |url=https://analyticalscience.wiley.com/do/10.1002/micro.2104/ |access-date=2023-03-29 |website=Wiley Analytical Science Magazine|doi= }} This is known as nucleation.{{Cite web |last=UCL |date=2016-12-09 |title=Understanding how ice crystals form in clouds |url=https://www.ucl.ac.uk/news/2016/dec/understanding-how-ice-crystals-form-clouds |access-date=2023-04-10 |website=UCL News |language=en}} Snowflakes form when additional vapor freezes onto an existing ice crystal.{{Cite web |title=Growth Rates and Habits of Ice Crystals between −20° and −70°C - Google Search |url=https://www.google.com/search?q=Growth+Rates+and+Habits+of+Ice+Crystals+between+%E2%88%9220%C2%B0+and+%E2%88%9270%C2%B0C |access-date=2024-03-10 |website=www.google.com}}{{Cite web |title=How do snowflakes form? Get the science behind snow |url=https://www.noaa.gov/stories/how-do-snowflakes-form-science-behind-snow |access-date=2023-03-30 |website=www.noaa.gov |date=19 December 2016 |language=en}}File:Снежинка на разноцветном фоне.JPG.]]

Supercooled water refers to water below its freezing point that is still liquid.{{Cite web |date=2014-12-20 |title=Supercool Clouds |url=https://earthobservatory.nasa.gov/images/84916/supercool-clouds#:~:text=Supercooling%20may%20sound%20exotic,%20but,of%20about%20-15%20degrees%20C. |access-date=2023-04-10 |website=earthobservatory.nasa.gov |language=en}} Ice crystals formed from supercooled water have stacking defects in their layered hexagons. This causes ice crystals to display trigonal or cubic symmetry depending on the temperature. Trigonal or cubic crystals form in the upper atmosphere where supercooling occurs.{{Cite journal |last1=Murray |first1=Benjamin J. |last2=Salzmann |first2=Christoph G. |last3=Heymsfield |first3=Andrew J. |last4=Dobbie |first4=Steven |last5=Neely |first5=Ryan R. |last6=Cox |first6=Christopher J. |date=2015-09-01 |title=Trigonal Ice Crystals in Earth's Atmosphere |journal=Bulletin of the American Meteorological Society |language=EN |volume=96 |issue=9 |pages=1519–1531 |doi=10.1175/BAMS-D-13-00128.1 |bibcode=2015BAMS...96.1519M |s2cid=120907603 |issn=0003-0007|doi-access=free }}{{Cite web |title=Cubic ice (ice Ic) structure |url=https://water.lsbu.ac.uk/water/cubic_ice.html |access-date=2023-04-10 |website=water.lsbu.ac.uk}}

Water can pass through laminated sheets of graphene oxide unlike smaller molecules such as helium. When squeezed between two layers of graphene, water forms square ice crystals at room temperature. Researchers believe high pressure and the van der Waals force, an attractive force present between all molecules, drives the formation. The material is a new crystalline phase of ice.{{Cite journal |last1=Algara-Siller |first1=G. |last2=Lehtinen |first2=O. |last3=Wang |first3=F. C. |last4=Nair |first4=R. R. |last5=Kaiser |first5=U. |last6=Wu |first6=H. A. |last7=Geim |first7=A. K. |last8=Grigorieva |first8=I. V. |date=2015 |title=Square ice in graphene nanocapillaries |url=https://www.nature.com/articles/nature14295 |journal=Nature |language=en |volume=519 |issue=7544 |pages=443–445 |doi=10.1038/nature14295 |pmid=25810206 |arxiv=1412.7498 |bibcode=2015Natur.519..443A |s2cid=4462633 |issn=1476-4687}}

File:Refraction-of-light Winter-Halo-2020.jpg created by light reflecting off of ice crystals in cirrus clouds. This specific halo is called a 46° halo.]]

Ice crystals create optical phenomena like diamond dust and halos in the sky due to light reflecting off of the crystals in a process called scattering.{{Citation |last=Gedzelman |first=S. D. |title=OPTICS, ATMOSPHERIC {{!}} Optical Phenomena |date=2003-01-01 |url=https://www.sciencedirect.com/science/article/pii/B0122270908002840 |encyclopedia=Encyclopedia of Atmospheric Sciences |pages=1583–1594 |editor-last=Holton |editor-first=James R. |access-date=2023-03-30 |place=Oxford |publisher=Academic Press |language=en |doi=10.1016/b0-12-227090-8/00284-0 |isbn=978-0-12-227090-1}}

Cirrus clouds and ice fog are made of ice crystals.{{Cite web |title=Ice fog |url=https://glossary.ametsoc.org/wiki/Ice_fog |access-date=2023-03-29 |website=Glossary of Meteorology |publisher=American Meteorological Society}} Cirrus clouds are often the sign of an approaching warm front, where warm and moist air rises and freezes into ice crystals.{{Cite web |title=Cirrus Clouds {{!}} Center for Science Education |url=https://scied.ucar.edu/image/cirrus-clouds |access-date=2023-03-30 |website=scied.ucar.edu}}{{Cite web |title=Cirrus clouds |url=https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/high-clouds/cirrus |access-date=2023-03-30 |website=Met Office |language=en}} Ice crystals rubbing against each other also produces lightning.{{Cite news |last=Plait |first=Phil |date=2016-11-16 |title=Ice Crystals Above Clouds Dance to the Tune of Electricity |language=en-US |work=Slate |url=https://slate.com/technology/2016/11/ice-crystals-above-clouds-dance-and-flash-according-to-electric-fields.html |access-date=2023-03-30 |issn=1091-2339}}{{Cite web |last=Canada |first=Environment and Climate Change |date=2011-04-15 |title=How lightning works |url=https://www.canada.ca/en/environment-climate-change/services/lightning/science/how-lightning-works.html |access-date=2023-03-30 |website=www.canada.ca}} The crystals normally fall horizontally,{{Cite journal |last1=Stillwell |first1=Robert A. |last2=Neely |first2=Ryan R. |last3=Thayer |first3=Jeffrey P. |last4=Walden |first4=Von P. |last5=Shupe |first5=Matthew D. |last6=Miller |first6=Nathaniel B. |date=2019-11-27 |title=Radiative Influence of Horizontally Oriented Ice Crystals over Summit, Greenland |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=124 |issue=22 |pages=12141–12156 |doi=10.1029/2018JD028963 |bibcode=2019JGRD..12412141S |s2cid=210640681 |issn=2169-897X|doi-access=free }} but electric fields can cause them to clump together and fall in other directions.{{Cite web |last=Libbrecht |first=Kenneth G. |title=Electric Snow Crystal Growth |url=https://www.its.caltech.edu/~atomic/snowcrystals/electric/electric.htm |access-date=2023-03-30 |website=www.its.caltech.edu}}{{Cite journal |last1=Latham |first1=J. |last2=Saunders |first2=C. P. R. |date=1964 |title=Aggregation of Ice Crystals in Strong Electric Fields |url=https://www.nature.com/articles/2041293a0 |journal=Nature |language=en |volume=204 |issue=4965 |pages=1293–1294 |doi=10.1038/2041293a0 |bibcode=1964Natur.204.1293L |s2cid=8747928 |issn=1476-4687}}

Image:Snow crystals.jpg ice crystals imaged with a scanning electron microscope. The colors are computer generated.]]The aerospace industry is working to design a radar that can detect ice crystal environments to discern hazardous flight conditions. Ice crystals can melt when they touch the surface of warm aircraft, and refreeze due to environmental conditions. The accumulation of ice around the engine damages the aircraft.{{Cite web |last=Heidman |first=Kelly |date=2015-08-11 |title=Flight Campaign Studies Radar Detection of Ice Crystal Icing |url=http://www.nasa.gov/image-feature/flight-campaign-studies-radar-detection-of-ice-crystal-icing |access-date=2023-03-30 |website=NASA}}{{Cite journal |last1=Lukas |first1=Jan |last2=Badin |first2=Pavel |date=2019-06-10 |title=High Altitude Ice Crystal Detection with Aircraft X-band Weather Radar |url=https://www.sae.org/publications/technical-papers/content/2019-01-2026/ |journal=SAE International Journal of Advances and Current Practices in Mobility |language=English |volume=2 |issue=1 |pages=256–264 |doi=10.4271/2019-01-2026 |s2cid=182542723 |issn=2641-9637}} Weather forecasting uses differential reflectivity weather radars to identify types of precipitation by comparing a droplet's horizontal and vertical lengths.{{Cite web |last=US Department of Commerce |first=NOAA |title=Dual-Pol Products |url=https://www.weather.gov/jan/dualpolupgrade-products |access-date=2023-03-30 |website=www.weather.gov |language=EN-US}} Ice crystals are larger in the horizontal direction and are thus detectable.

• Snow
• Snowflake
• Ice spike
• Ice lens
• Icicle

{{reflist}}

• [http://www.its.caltech.edu/~atomic/snowcrystals/ SnowCrystals.com!], at Caltech
• [https://web.archive.org/web/20080316222148/http://amsglossary.allenpress.com/glossary/search?id=ice-crystal1 American Meteorological Society Glossary]

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Crystal

Crystal

Category:Clouds, fog and precipitation

Category:Atmospheric optical phenomena