Editing Ice (section)

==Natural formation==
[[File:Tsu_Lake_Ice_Circle.jpg|thumb|Frozen landscape in the [[Northwest Territories]] of [[Canada]]. A large ice circle can be clearly seen floating on water.<ref>{{Cite journal |last=Dorbolo |first=S. |date=2016 |title=Rotation of melting ice disks due to melt fluid flow |url=https://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.033112 |journal=Physical Review E |volume=93 |issue=3 |page=033112 |doi=10.1103/PhysRevE.93.033112|pmid=27078452 |bibcode=2016PhRvE..93c3112D }}</ref><ref>{{Cite journal |last1=Stepanova |first1=E. V. |last2=Chaplina |first2=T. O. |date=December 2019 |title=Vortex Flow Formation by a Melting Ice Block |url=http://link.springer.com/10.1134/S0015462819070140 |journal=Fluid Dynamics |language=en |volume=54 |issue=7 |pages=1002–1008 |doi=10.1134/S0015462819070140 |bibcode=2019FlDy...54.1002S |issn=0015-4628}}</ref>]] 
The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the ''[[cryosphere]].'' Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and [[snowpack]]s are an important storage mechanism for fresh water; over time, they may sublimate or melt. [[Snowmelt]] is an important source of seasonal fresh water.<ref name="HKH2019Cryo" /><ref name="HKH2019Water" /> The [[World Meteorological Organization]] defines several kinds of ice depending on origin, size, shape, influence and so on.<ref name=wmo>[http://www.aari.nw.ru/gdsidb/XML/volume1.php?lang1=0&lang2=1&arrange=0&self=0 "WMO SEA-ICE NOMENCLATURE"] {{webarchive |url=https://web.archive.org/web/20130605124444/http://www.aari.nw.ru/gdsidb/XML/volume1.php?lang1=0&lang2=1&arrange=0&self=0 |date=5 June 2013 }} ([http://www.aari.nw.ru/gdsidb/XML/wmo_259.php Multi-language] {{webarchive |url=https://web.archive.org/web/20120414141500/http://www.aari.nw.ru/gdsidb/XML/wmo_259.php |date=14 April 2012 }}) ''World Meteorological Organization'' / ''[[Arctic and Antarctic Research Institute]]''. Retrieved 8 April 2012.</ref> [[Clathrate hydrate]]s are forms of ice that contain gas molecules trapped within its crystal lattice.<ref>{{Cite journal|doi=10.1021/ie00019a001|title=Clathrate hydrates|year=1993 |last1=Englezos |first1=Peter|journal=Industrial & Engineering Chemistry Research |volume=32|issue=7|pages=1251–1274}}</ref><ref>{{citation |publisher=U.S. Geological Survey |url=https://woodshole.er.usgs.gov/project-pages/hydrates/what.html |date=31 August 2009 |access-date=28 December 2014 |title=Gas Hydrate: What is it? |url-status=dead |archive-url=https://web.archive.org/web/20120614141539/http://woodshole.er.usgs.gov/project-pages/hydrates/what.html |archive-date=June 14, 2012}}</ref>

=== In the oceans ===
{{main|Sea ice}}
Ice that is found at sea may be in the form of [[drift ice]] floating in the water, [[fast ice]] fixed to a shoreline or [[anchor ice]] if attached to the seafloor.<ref>{{cite report |date=2014 |title=WMO Sea-ice Nomenclature |url=https://library.wmo.int/records/item/41953-wmo-sea-ice-nomenclature |publisher=Secretariat of the World Meteorological Organization }}</ref> Ice which [[Ice calving|calves]] (breaks off) from an [[ice shelf]] or a coastal glacier may become an iceberg.<ref>{{cite journal | last1 = Benn | first1 = D. | last2 = Warren | first2 = C. | last3 = Mottram | first3 = R. | year = 2007 | title = Calving processes and the dynamics of calving glaciers | url = http://stuff.mit.edu/~heimbach/papers_glaciology/earthscirev_benn_etal_2007_calving.pdf | journal = Earth-Science Reviews | volume = 82 | issue = 3–4| pages = 143–179 | doi=10.1016/j.earscirev.2007.02.002| bibcode = 2007ESRv...82..143B }}</ref> The aftermath of calving events produces a loose mixture of snow and ice known as [[Ice mélange]].<ref>{{Cite journal|last=Robel|first=Alexander A.|date=2017-03-01|title=Thinning sea ice weakens buttressing force of iceberg mélange and promotes calving|journal=Nature Communications|language=en|volume=8|pages=14596|doi=10.1038/ncomms14596|pmid=28248285|pmc=5339875|bibcode=2017NatCo...814596R |issn=2041-1723}}</ref> 

Sea ice forms in several stages. At first, small, millimeter-scale crystals accumulate on the water surface in what is known as [[frazil ice]]. As they become somewhat larger and more consistent in shape and cover, the water surface begins to look "oily" from above, so this stage is called [[grease ice]].<ref>{{Cite book |last1=Smedsrud |first1=Lars H. |last2=Skogseth |first2=Ragnheid |title=Field Measurements of Arctic Grease Ice Properties and Processes |publisher=Cold Regions Science and Technology 44 |year=2006 |pages=171–183 }}</ref> Then, ice continues to clump together, and solidify into flat cohesive pieces known as [[ice floe]]s. Ice floes are the basic building blocks of sea ice cover, and their horizontal size (defined as half of their [[diameter]]) varies dramatically, with the smallest measured in centimeters and the largest in hundreds of kilometers.<ref>{{cite journal |last1=Roach |first1=Lettie A. |last2=Horvat |first2=Christopher |last3=Dean |first3=Samuel M. |last4=Bitz |first4=Cecilia M. |title=An Emergent Sea Ice Floe Size Distribution in a Global Coupled Ocean-Sea Ice Model |journal= Journal of Geophysical Research: Oceans|date=6 May 2018 |volume=123 |issue=6 |pages=4322–4337 |doi=10.1029/2017JC013692 |bibcode=2018JGRC..123.4322R }}</ref> An area which is over 70% ice on its surface is said to be covered by pack ice.<ref>{{cite book|author1=Qin Zhang|author2=Roger Skjetne|title=Sea Ice Image Processing with MATLAB|url=https://books.google.com/books?id=DuJLDwAAQBAJ&pg=PP43|date=13 February 2018|publisher=CRC|isbn=978-1-351-06918-2|page=43}}</ref> 

Fully formed sea ice can be forced together by currents and winds to form [[Pressure ridge (ice)|pressure ridges]] up to {{convert|12|m}} tall.<ref>{{Cite journal |last1=Leppäranta |first1=Matti |last2=Hakala |first2=Risto |date=25 April 1991 |title=The structure and strength of first-year ice ridges in the Baltic Sea |journal=Cold Regions Science and Technology |volume=20 |issue=3 |pages=295–311 |doi=10.1016/0165-232X(92)90036-T }}</ref> On the other hand, active wave activity can reduce sea ice to small, regularly shaped pieces, known as [[pancake ice]].<ref>{{Cite journal|last=Squire|first=Vernon A.|date=2020|title=Ocean Wave Interactions with Sea Ice: A Reappraisal |journal=Annual Review of Fluid Mechanics |volume=52 |issue=1 |pages=37–60 |bibcode=2020AnRFM..52...37S |doi=10.1146/annurev-fluid-010719-060301|s2cid=198458049 |issn=0066-4189 |doi-access=free}}</ref> Sometimes, wind and wave activity "polishes" sea ice to perfectly spherical pieces known as [[ice eggs]].<ref>{{Cite news |date=2019-11-07 |title='Ice eggs' cover Finland beach in rare weather event |language=en-GB |work=BBC News |url=https://www.bbc.com/news/world-europe-50338447 |access-date=2022-04-22}}</ref><ref>{{Cite web |last=geographyrealm |date=2019-11-14 |title=How Ice Balls Form |url=https://www.geographyrealm.com/how-ice-balls-form/ |access-date=2022-04-23 |website=Geography Realm |language=en-US}}</ref>

<gallery mode="packed" heights="150px">
File:GreaseIce2.jpg|Grease ice in the [[Bering Sea]]
File:Greenland East Coast 7.jpg|Loose drift ice on the east coast of Greenland
File:Jää on kulmunud pallideks (Looduse veidrused). 05.jpg|Ice eggs (diameter 5–10 cm) on Stroomi Beach, Tallinn, Estonia
File:IceNomenclature-2LightPack.jpg|Ice floes in Antarctica, 1919
File:Ridge MOSAiC.jpg|A first-year sea ice ridge in the Central Arctic, photographed by the [[MOSAiC Expedition|MOSAiC expedition]] on July 4, 2020
File:A_Mélange_of_Ice_-_NASA_Earth_Observatory.jpg|Ice mélange on Greenland's western coast, 2012
File:Anchor ice under sea ice.JPG|Anchor ice on the seafloor at [[McMurdo Sound]], Antarctica.
</gallery>

=== On land ===
[[File:AA bedrock surface.4960.tif|thumb|[[NASA]] image of the Antarctic ice sheet]]
The largest ice formations on Earth are the two [[ice sheet]]s which almost completely cover the world's largest island, [[Greenland]], and the continent of [[Antarctica]]. These ice sheets have an average thickness of over {{convert|1|km|mi|1|abbr=on}} and have existed for millions of years.<ref name="BBC2017">{{cite web |title=How Greenland would look without its ice sheet |date=14 December 2017 |url=https://www.bbc.com/news/science-environment-42260580 |publisher=[[BBC News]] |access-date=7 December 2023 |archive-date=7 December 2023 |archive-url=https://web.archive.org/web/20231207201039/https://www.bbc.com/news/science-environment-42260580 |url-status=live }}</ref><ref name="Fretwell2013" /> 

Other major ice formations on land include [[ice cap]]s, [[ice field]]s, [[ice stream]]s and [[glacier]]s. In particular, the [[Hindu Kush]] region is known as the Earth's "Third Pole" due to the large number of glaciers it contains. They cover an area of around {{cvt|80,000|sqkm|sqmi}}, and have a combined volume of between 3,000-4,700&nbsp;km<sup>3</sup>.<ref name="HKH2019Cryo">{{Cite book |last1=Bolch |first1=Tobias |last2=Shea |first2=Joseph M. |last3=Liu |first3=Shiyin |last4=Azam |first4=Farooq M. |last5=Gao |first5=Yang |last6=Gruber |first6=Stephan |last7=Immerzeel |first7=Walter W. |last8=Kulkarni |first8=Anil |last9=Li |first9=Huilin |last10=Tahir |first10=Adnan A. |last11=Zhang |first11=Guoqing |last12=Zhang |first12=Yinsheng |title=The Hindu Kush Himalaya Assessment |date=5 January 2019 |chapter=Status and Change of the Cryosphere in the Extended Hindu Kush Himalaya Region |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-92288-1_7 |pages=209–255 |doi=10.1007/978-3-319-92288-1_7 |isbn=978-3-319-92287-4 |s2cid=134814572 }}</ref> These glaciers are nicknamed "Asian water towers", because their meltwater run-off feeds into rivers which provide water for an estimated two billion people.<ref name="HKH2019Water">{{Cite book |last1=Scott |first1=Christopher A. |last2=Zhang |first2=Fan |last3=Mukherji |first3=Aditi |last4=Immerzeel |first4=Walter |last5=Mustafa |first5=Daanish |last6=Bharati |first6=Luna |title=The Hindu Kush Himalaya Assessment |date=5 January 2019 |chapter=Water in the Hindu Kush Himalaya |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-92288-1_8 |pages=257–299 |doi=10.1007/978-3-319-92288-1_8 |isbn=978-3-319-92287-4 |s2cid=133800578 }}</ref>

[[Permafrost]] refers to [[soil]] or underwater [[sediment]] which continuously remains below {{cvt|0|C|F}} for two years or more.<ref>{{cite web |url=https://climate.mit.edu/explainers/permafrost |title=Permafrost |last1=McGee |first1=David |last2=Gribkoff |first2=Elizabeth |date=4 August 2022 |website=MIT Climate Portal |access-date=27 September 2023 }}</ref> The ice within permafrost is divided into four categories: pore ice, vein ice (also known as ice wedges), buried surface ice and intrasedimental ice (from the freezing of underground waters).<ref>{{Cite journal |last1=Lacelle |first1=Denis |last2=Fisher |first2=David A. |last3=Verret |first3=Marjolaine |last4=Pollard |first4=Wayne |date=17 February 2022 |title=Improved prediction of the vertical distribution of ground ice in Arctic-Antarctic permafrost sediments |journal=Communications Earth & Environment |volume=3 |issue=31 |page=31 |doi=10.1038/s43247-022-00367-z |bibcode=2022ComEE...3...31L |s2cid=246872753 }}</ref> One example of ice formation in permafrost areas is [[aufeis]] - layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.<ref>{{Cite journal |last1=Huryn |first1=Alexander D. |last2=Gooseff |first2=Michael N. |last3=Hendrickson |first3=Patrick J. |last4=Briggs |first4=Martin A. |last5=Tape |first5=Ken D. |last6=Terry |first6=Neil C. |date=2020-10-13 |title=Aufeis fields as novel groundwater-dependent ecosystems in the arctic cryosphere |journal=Limnology and Oceanography |volume=66 |issue=3 |pages=607–624 |doi=10.1002/lno.11626 |s2cid=225139804 |issn=0024-3590|doi-access=free }}</ref> [[Snow line]] and [[snow field]]s are two related concepts, in that snow fields accumulate on top of and ablate away to the equilibrium point (the snow line) in an ice deposit.<ref>{{Cite book |last1=Johnson |first1=Chris |url=https://slcc.pressbooks.pub/introgeology/chapter/14-glaciers/ |title=An Introduction to Geology |last2=Affolter |first2=Matthew D. |last3=Inkenbrandt |first3=Paul |last4=Mosher |first4=Cam |date=July 1, 2017 |chapter=14 Glaciers}}</ref>

===On rivers and streams===
[[File:Frozen rivulet in Pennsylvania.JPG|thumb|left|A small frozen [[rivulet]]]]
Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. [[Ice jam]]s (sometimes called "ice dams"), when broken chunks of ice pile up, are the greatest ice hazard on rivers. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Ice jams can cause some [[hydropower]] industrial facilities to completely shut down. An ice dam is a blockage from the movement of a glacier which may produce a [[proglacial lake]]. Heavy ice flows in rivers can also damage vessels and require the use of an [[icebreaker]] vessel to keep navigation possible.<ref>{{cite web|url=http://www.nws.noaa.gov/floodsafety/ice_jam.shtml |title=Ice Jams |publisher=Nws.noaa.gov |date=2013-03-13 |access-date=11 January 2014 }}</ref><ref>{{Cite news|url=https://www.popularmechanics.com/science/environment/a473/2272511/ |title=Ice Dams: Taming An Icy River|last=Staff writer|date=7 February 2006 |work=Popular Mechanics|access-date=27 March 2018 |language=en-US}}</ref>

[[Ice disc]]s are circular formations of ice floating on river water. They form within [[Eddy (fluid dynamics)|eddy current]]s, and their position results in asymmetric melting, which makes them continuously rotate at a low speed.<ref>{{Cite web |url=http://modernnotion.com/crop-circles-ice-ice-circles-form/ |title=Crop Circles in the Ice: How Do Ice Circles Form? |date=22 December 2015 |website=Modern Notion |language=en-US |access-date=16 January 2019 |archive-date=8 August 2017 |archive-url=https://web.archive.org/web/20170808193720/http://modernnotion.com/crop-circles-ice-ice-circles-form/ |url-status=dead }}</ref><ref>{{cite journal |last1=Dorbolo |first1=S |last2=Adami |first2=N. |last3=Dubois |first3=C. |last4=Caps |first4=H. |last5=Vandewalle |first5=N. |last6=Barbois-Texier |first6=B. |title=Rotation of melting ice disks due to melt fluid flow |journal=Phys. Rev. E |year=2016 |volume=93 |issue=3 |pages=1–5 |doi=10.1103/PhysRevE.93.033112 |pmid=27078452 |bibcode=2016PhRvE..93c3112D |hdl=2268/195696 |s2cid=118380381 |url=https://orbi.uliege.be/handle/2268/195696|arxiv=1510.06505 }}</ref>

===On lakes{{anchor|Ice_on_lakes}}===
[[File:Candle_Ice.jpg|thumb|300x300px|Candle ice in Lake Otelnuk, [[Quebec, Canada]]]]
Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: primary, secondary, superimposed and agglomerate.<ref>Petrenko, Victor F. and Whitworth, Robert W. (1999) ''Physics of ice''. Oxford: Oxford University Press, pp. 27–29, {{ISBN|0191581348}}</ref><ref>Eranti, E. and Lee, George C. (1986) ''Cold region structural engineering''. New York: McGraw-Hill, p. 51, {{ISBN|0070370346}}.</ref> Primary ice forms first. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow. Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in the ice which often settles when loaded with snow.  An [[ice shove]] occurs when ice movement, caused by ice expansion and/or wind action, occurs to the extent that ice pushes onto the shores of lakes, often displacing sediment that makes up the shoreline.<ref>{{cite journal |last1=Dionne |first1=J |title=Ice action in the lacustrine environment. A review with particular reference to subarctic Quebec, Canada |journal=Earth-Science Reviews |date=November 1979 |volume=15 |issue=3 |pages=185–212 |doi=10.1016/0012-8252(79)90082-5 |bibcode=1979ESRv...15..185D }}</ref>

[[Shelf ice]] is formed when floating pieces of ice are driven by the wind piling up on the windward shore. This kind of ice may contain large air pockets under a thin surface layer, which makes it particularly hazardous to walk across it.<ref>{{Cite news |last=Schwarz |first=Phil |date=19 February 2018 |title=Dangerous shelf ice forms along Lake Michigan |url=https://abc7chicago.com/3109973/ |work=abc7chicago.com |accessdate=2020-02-05 }}</ref> Another dangerous form of [[rotten ice]] to traverse on foot is candle ice, which develops in columns perpendicular to the surface of a lake. Because it lacks a firm horizontal structure, a person who has fallen through has nothing to hold onto to pull themselves out.<ref>{{Cite encyclopedia|title=Candle ice|encyclopedia=Glossary of Meteorology|publisher=[[American Meteorological Society]]|url=https://glossary.ametsoc.org/wiki/Candle_ice|access-date=2021-03-17|date=2012-02-20}}</ref>

=== As precipitation ===
{{Main|Precipitation}}
====Snow and freezing rain ====
{{Main|Snow|Snowflake}}
[[File:SnowflakesWilsonBentley.jpg|thumb|[[Snowflake]]s by [[Wilson Bentley]], 1902]]
Snow crystals form when tiny [[supercool]]ed cloud droplets (about 10&nbsp;[[μm]] in diameter) [[freezing|freeze]]. These droplets are able to remain liquid at temperatures lower than {{convert|-18|C|K F}}, because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus". Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than {{convert|-35|C|K F}}.<ref name=Mason>{{cite book|author = Mason, Basil John| publisher= Clarendon Press| isbn= 978-0-19-851603-3|year = 1971|title = Physics of Clouds|url = https://archive.org/details/physicsofclouds0000maso|url-access = registration}}</ref> In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor&nbsp;– what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,<ref name=Christner2008>{{cite journal |last1=Christner |first1=Brent C. |last2=Morris |first2=Cindy E. |last3=Foreman |first3=Christine M. |last4=Cai |first4=Rongman |last5=Sands |first5=David C. |title=Ubiquity of Biological Ice Nucleators in Snowfall |journal=Science |date=29 February 2008 |volume=319 |issue=5867 |pages=1214 |doi=10.1126/science.1149757 |pmid=18309078 |bibcode=2008Sci...319.1214C |citeseerx=10.1.1.714.4002 |s2cid=39398426 }}</ref> although to what extent is unclear. Artificial nuclei are used in [[cloud seeding]].<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|title=Cloud seeding|author=Glossary of Meteorology|year=2009|access-date=28 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20120315161127/http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|archive-date=15 March 2012}}</ref> The droplet then grows by condensation of water vapor onto the ice surfaces.<ref>{{cite journal |last1=Pelley |first1=Janet |title=Does cloud seeding really work? |journal=Chemical and Engineering News|date=30 May 2016|volume=94 |issue=22 |pages=18–21 |url=http://cen.acs.org/articles/94/i22/Does-cloud-seeding-really-work.html |access-date=26 May 2024 |archive-date=10 November 2016 |archive-url=https://web.archive.org/web/20161110235130/http://cen.acs.org/articles/94/i22/Does-cloud-seeding-really-work.html |url-status=live}}</ref>

[[Ice storm]] is a type of winter storm characterized by [[freezing rain]], which produces a [[glaze ice|glaze]] of ice on surfaces, including roads and [[power line]]s. In the United States, a quarter of winter weather events produce glaze ice, and utilities need to be prepared to minimize damages.<ref>{{cite journal |last1=Sanders |first1=Kristopher J. |last2=Barjenbruch |first2=Brian L. |title=Analysis of Ice-to-Liquid Ratios during Freezing Rain and the Development of an Ice Accumulation Model |journal=Weather Forecasting |date=1 August 2016 |volume=31 |issue=4 |pages=1041–1060 |doi=10.1175/WAF-D-15-0118.1 |bibcode=2016WtFor..31.1041S }}</ref>

==== Hard forms ====
{{Further|Ice crystal}}
[[File:Granizo.jpg|right|thumb|A large hailstone, about {{convert|6|cm|in|abbr=on}} in diameter]]
[[Hail]] forms in storm [[cloud]]s when [[supercooled]] water droplets freeze on contact with [[condensation nuclei]], such as [[dust]] or [[dirt]]. The storm's [[updraft]] blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of {{convert|5|mm|in}} or more.<ref name="gloss">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=hail1|title=Hail|year=2009|access-date=15 July 2009|author=Glossary of Meteorology|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20100725142407/http://amsglossary.allenpress.com/glossary/search?id=hail1|archive-date=25 July 2010}}</ref> Within [[METAR]] code, GR is used to indicate larger hail, of a diameter of at least {{convert|6.4|mm|in}} and GS for smaller.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar+taf/sametara.htm|title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]] via the Internet Wayback Machine|access-date=29 August 2009|date=10 April 2007|url-status=dead|archive-url=https://web.archive.org/web/20080501074014/http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm|archive-date=1 May 2008}}</ref> Stones of {{Convert|0.75|in|mm|order=flip}}, {{Convert|1.0|in|mm|order=flip}} and {{Convert|1.75|in|mm|order=flip}} are the most frequently reported hail sizes in North America.<ref>{{cite web|url=http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|title=P9.5 Evaluation of an Alberta Hail Growth Model Using Severe Hail Proximity Soundings in the United States|author1=Jewell, Ryan|author2=Brimelow, Julian|date=17 August 2004|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090507044027/http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|archive-date=7 May 2009}}</ref> Hailstones can grow to {{convert|15|cm|in|0}} and weigh more than {{convert|0.5|kg|lb|1}}.<ref>{{cite web|url=http://www.photolib.noaa.gov/htmls/nssl0001.htm|title=Aggregate hailstone|author=National Severe Storms Laboratory|publisher=National Oceanic and Atmospheric Administration|date=23 April 2007|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090810182627/http://www.photolib.noaa.gov/htmls/nssl0001.htm|archive-date=10 August 2009}}</ref> In large hailstones, [[latent heat]] released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.<ref>{{cite journal|title=Modeling Maximum Hail Size in Alberta Thunderstorms|journal=Weather and Forecasting|author1=Brimelow, Julian C. |author2=Reuter, Gerhard W. |author3=Poolman, Eugene R. |pages=1048–1062|volume=17|issue=5|doi=10.1175/1520-0434(2002)017<1048:MMHSIA>2.0.CO;2|bibcode = 2002WtFor..17.1048B|year=2002|doi-access=free}}</ref> The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.<ref>{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Hail Fact Sheet|date=10 April 2000|author=Marshall, Jacque|access-date=15 July 2009|publisher=University Corporation for Atmospheric Research|url-status=dead|archive-url=https://web.archive.org/web/20091015141754/http://www.ucar.edu/communications/factsheets/Hail.html|archive-date=15 October 2009}}</ref>
[[File:2013-02-23_03_59_28_Graupel_(snow_pellets)_in_Elko,_Nevada.JPG|thumb|right|Soft hail, or graupel, in [[Nevada]]]]
Hail forms in strong [[thunderstorm]] clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing {{convert|0|C|F|0}}.<ref name="gloss"/> Hail-producing clouds are often identifiable by their green coloration.<ref>{{cite web|url=http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-url=https://web.archive.org/web/20100306021712/http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-date=6 March 2010|title=Hail storms rock southern Qld|publisher=Australian Broadcasting Corporation|date=19 October 2004|access-date=15 July 2009}}</ref><ref>{{cite web|url=http://australiasevereweather.com/storm_news/arc1997.htm|title=Severe Thunderstorm Images of the Month Archives|year=1997|author1=Bath, Michael|author2=Degaura, Jimmy|access-date=15 July 2009|url-status=live|archive-url=http://archive.wikiwix.com/cache/20110713110215/http://australiasevereweather.com/storm_news/arc1997.htm|archive-date=13 July 2011}}</ref> The growth rate is maximized at about {{convert|-13|C|F|0}}, and becomes vanishingly small much below {{convert|-30|C|F|0}} as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of {{convert|11000|ft|m}}.<ref>{{cite web|url=http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-url=https://web.archive.org/web/20030320222147/http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-date=20 March 2003|title=Meso-Analyst Severe Weather Guide|author=Wolf, Pete|date=16 January 2003|access-date=16 July 2009|publisher=University Corporation for Atmospheric Research}}</ref> [[Entrainment (meteorology)|Entrainment]] of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporative cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the [[atmosphere]] over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.<ref>{{cite book|url=https://books.google.com/books?id=UbtG3vFfNtoC&pg=PA41|title=Climate, change and risk|author1=Downing, Thomas E. |author2=Olsthoorn, Alexander A. |author3=Tol, Richard S. J. |pages=41–43|publisher=Routledge|year=1999|isbn=978-0-415-17031-4}}</ref>
[[File:Sleet on the ground.jpg|thumb|An accumulation of ice pellets]]
Ice pellets ([[METAR]] code ''PL''<ref name="METAR"/>) are a form of precipitation consisting of small, [[translucent]] balls of ice, which are usually smaller than hailstones.<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=hail|title=Hail (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20071127004804/http://www.weather.gov/glossary/index.php?word=hail|archive-date=27 November 2007}}</ref> This form of precipitation is also referred to as "sleet" by the United States [[National Weather Service]].<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=sleet|title=Sleet (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20070218030309/http://www.weather.gov/glossary/index.php?word=sleet|archive-date=18 February 2007}}</ref> (In [[British English]] "sleet" refers to [[Rain and snow mixed|a mixture of rain and snow]].) Ice pellets typically form alongside freezing rain, when a wet [[warm front]] ends up between colder and drier atmospheric layers. There, raindrops would both freeze and shrink in size due to evaporative cooling.<ref>{{cite web|publisher=Weatherquestions.com|url=http://www.weatherquestions.com/What_causes_ice_pellets.htm|title=What causes ice pellets (sleet)?|access-date=8 December 2007|url-status=live|archive-url=https://web.archive.org/web/20071130071143/http://www.weatherquestions.com/What_causes_ice_pellets.htm|archive-date=30 November 2007}}</ref> So-called snow pellets, or [[graupel]], form when multiple water droplets freeze onto snowflakes until a soft ball-like shape is formed.<ref>{{cite web | url = https://sgil.ba.ars.usda.gov/snowsite/rimegraupel/rg.html | title = Rime and Graupel | website = [[U.S. Department of Agriculture]] Electron Microscopy Unit, Beltsville Agricultural Research Center | access-date = 2020-03-23 | archive-url = https://web.archive.org/web/20170711205706/https://sgil.ba.ars.usda.gov/snowsite/rimegraupel/rg.html | archive-date = 2017-07-11}}</ref> So-called "[[diamond dust]]", (METAR code ''IC''<ref name="METAR" />) also known as ice needles or ice crystals, forms at temperatures approaching {{convert|-40|C|F}} due to air with slightly higher moisture from aloft mixing with colder, surface-based air.<ref name="glossdia">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|title=Diamond Dust|author=Glossary of Meteorology|date=June 2000|publisher=American Meteorological Society|archive-url=https://web.archive.org/web/20090403084329/http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|archive-date=3 April 2009|url-status=dead|access-date=21 January 2010}}</ref>

=== On surfaces ===
As water drips and re-freezes, it can form hanging [[icicle]]s, or [[stalagmite]]-like structures on the ground.<ref>{{cite journal|last=Makkonen |first=Lase |title=Models for the growth of rime, glaze, icicles and wet snow deposits on structures |journal=Philosophical Transactions of the Royal Society of London A |date=15 November 2000 |volume=358 |issue=1776 |pages=2913–2939 |doi=10.1098/rsta.2000.0690 }}</ref> On sloped roofs, buildup of ice can produce an [[Ice dam (roof)|ice dam]], which stops melt water from draining properly and potentially leads to damaging leaks.<ref>{{cite web |title=Dealing with and preventing ice dams |url=https://extension.umn.edu/protecting-home-rain-and-ice/dealing-and-preventing-ice-dams |publisher=[[University of Minnesota]] Extension |access-date=10 April 2024 }}</ref> More generally, [[water vapor]] depositing onto surfaces due to high [[relative humidity]] and then freezing results in various forms of [[atmospheric icing]], or [[frost]]. Inside buildings, this can be seen as ice on the surface of un-insulated windows.<ref>{{cite web |url=http://www.weatherquestions.com/What_causes_frost.htm |title=What causes frost? |access-date=2007-12-05 |url-status=live |archive-url=https://web.archive.org/web/20071210230539/http://www.weatherquestions.com/What_causes_frost.htm |archive-date=2007-12-10 }}</ref> Hoar frost is common in the environment, particularly in the low-lying areas such as [[valley]]s.<ref>{{cite web|url=http://www.weatheronline.co.uk/reports/wxfacts/Frost-hollow.htm|title=Weather Facts: Frost hollow – Weather UK – weatheronline.co.uk|work=weatheronline.co.uk|url-status=live|archive-url=https://web.archive.org/web/20130212022607/http://www.weatheronline.co.uk/reports/wxfacts/Frost-hollow.htm|archive-date=2013-02-12}}</ref> In Antarctica, the temperatures can be so low that [[electrostatic attraction]] is increased to the point hoarfrost on snow sticks together when blown by wind into [[tumbleweed]]-like balls known as [[yukimarimo]].<ref>{{Cite journal|last1=Kameda|first1=T.|last2=Yoshimi|first2=H.|last3=Azuma|first3=N.|last4=Motoyama|first4=H.|date=1999|title=Observation of "yukimarimo" on the snow surface of the inland plateau, Antarctic ice sheet|journal=Journal of Glaciology|language=en|volume=45|issue=150|pages=394–396|doi=10.1017/S0022143000001891|bibcode=1999JGlac..45..394K|issn=0022-1430|doi-access=free}}</ref> 

Sometimes, drops of water crystallize on cold objects as [[Rime ice|rime]] instead of glaze. Soft rime has a density between a quarter and two thirds that of pure ice,<ref>{{cite journal |last1=Podolskiy |first1=Evgeny Andreevich |last2=Nygaard |first2=Bjørn Egil Kringlebotn |last3=Nishimura |first3=Kouichi |last4=Makkonen |first4=Lasse |last5=Lozowski |first5=Edward Peter |title=Study of unusual atmospheric icing at Mount Zao, Japan, using the Weather Research and Forecasting model |journal=Journal of Geophysical Research: Atmospheres |date=27 June 2012 |volume=112 |issue=D2 |doi=10.1029/2011JD017042 |bibcode=2012JGRD..11712106P }}</ref> due to a high proportion of trapped air, which also makes soft rime appear white. Hard rime is denser, more transparent, and more likely to appear on ships and aircraft.<ref>{{Cite web |title=hard rime (Glossary of Meteorology) |url=https://glossary.ametsoc.org/wiki/Hard_rime |date=30 March 2024 |publisher=American Meteorological Society |language=en-US |access-date=11 April 2024 }}</ref><ref>{{Cite web |title=soft rime (Glossary of Meteorology) |url=https://glossary.ametsoc.org/wiki/Soft_rime |date=30 March 2024 |publisher=American Meteorological Society |language=en-US |access-date=11 April 2024 }}</ref> Cold wind specifically causes what is known as ''advection frost'' when it collides with objects. When it occurs on plants, it often causes damage to them.<ref>{{Cite journal |last1=Beerling |first1=D. J. |last2=Terry |first2=A. C. |last3=Mitchell |first3=P. L. |last4=Callaghan |first4=T. V. |last5=Gwynn-Jones |first5=D. |last6=Lee |first6=J. A. |date=April 2001 |title=Time to chill: effects of simulated global change on leaf ice nucleation temperatures of subarctic vegetation |url=http://doi.wiley.com/10.2307/2657062 |journal=American Journal of Botany |language=en |volume=88 |issue=4 |pages=628–633 |doi=10.2307/2657062|jstor=2657062 |pmid=11302848 }}</ref> Various methods exist to protect agricultural crops from frost - from simply covering them to using wind machines.<ref name="Pan2023" /><ref>{{cite web |date=June 2010 |title=Wind machines for minimizing cold injury to horticultural crops |url=https://www.ontario.ca/page/wind-machines-minimizing-cold-injury-horticultural-crops |publisher=Ontario state government |access-date=30 May 2024 }}</ref> In recent decades, [[irrigation sprinkler]]s have been calibrated to spray just enough water to preemptively create a layer of ice that would form slowly and so avoid a sudden temperature shock to the plant, and not be so thick as to cause damage with its weight.<ref name="Pan2023">{{cite journal |last1=Pan |first1=Qingmin |last2=Lu |first2=Yongzong |last3=Hu |first3=Huijie |last4=Hu |first4=Yongguang |title=Review and research prospects on sprinkler irrigation frost protection for horticultural crops |journal=Scientia Horticulture |date=15 December 2023 |volume=326 |doi=10.1016/j.scienta.2023.112775 }}</ref>

<gallery mode="packed" heights="150px">
File:Saint-Amant_16_Gelée_blanche_2008.jpg|Grass partially covered in hoarfrost, 2008
File:Dülmen, Hausdülmen, Distel -- 2021 -- 5079.jpg|Frost on a thistle in [[Dülmen|Hausdülmen]], [[North Rhine-Westphalia]], Germany
File:Frostweb.jpg|A [[spiderweb]] covered in frost
File:Icy Japanese Maple branch, Boxborough, Massachusetts, 2008.jpg|Ice on [[deciduous tree]] after freezing rain
File:Ice on stairway, 1968 (32085554416).jpg|Icicles on a [[stairway]] in [[Seattle]], 1968
File:WindowFrostNewmarketOntario1986.jpg|Fern frost on a window
File:HoarFrost.jpg|Hoar frost atop snow
File:Yukimarimo south pole dawn 2009.jpg|Yukimarimo at [[South Pole Station]], Antarctica, in 2008
</gallery>