Graupel pellets in morning, having fallen the previous day
Graupel is distinct from hail and ice pellets in both formation and appearance. However, both hail and graupel are common in thunderstorms with cumulonimbus clouds, though graupel also falls in winter storms, and at higher elevations as well. [3] The METAR code for graupel is GS.
Under some atmospheric conditions, snow crystals may encounter supercooled water droplets. These droplets, which have a diameter of about 10 μm (0.00039 in) on average, can exist in the liquid state at temperatures as low as −40 °C (−40 °F), far below the normal freezing point as long as above the homogeneous nucleation point of water. Contact between a snow crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystal. This process of crystal growth is known as accretion. Crystals that exhibit frozen droplets on their surfaces are often referred to as rimed. When this process continues so that the shape of the original snow crystal is no longer identifiable and has become ball-like, the resulting crystal is referred to as graupel.[4]
As graupel falls, it often deforms into a conical shape. This conical shape, in turn, determines which direction it falls and how far it travels as it falls. Small graupel particles with a base diameter less than 1mm generally fall with the conical base down, but if the particle is between 1mm and 3mm persistent oscillations around the center of the conical base appear, and if larger than 3mm the graupel particle will start to tumble. As the base diameter increases, conical graupel particles generally further horizontally from where it initially fell.[5]
Graupel was formerly referred to by meteorologists as "soft hail." Graupel is distinguishable from true hail in both the shape and strength of the pellet and, in some cases, the circumstances in which it falls. Ice from hail is formed in hard, relatively uniform layers and usually falls only during thunderstorms. Graupel forms fragile, soft, oblong crystals and falls in place of typical snowflakes in wintry mix situations, often in concert with ice pellets. However, graupel does also occur in thunderstorms. Graupel is also fragile enough that it will typically fall apart when pressed on.[6]
Microscopic structureedit
The frozen droplets on the surface of rimed crystals are difficult to see even when zoomed in, and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument.
However, observations of snow crystals with a low-temperature scanning electron microscope (LT-SEM) clearly show frozen cloud droplets measuring up to 50 μm (0.002 in) on the surface of the crystals. The rime has been observed on all four basic forms of snow crystals, including plates, dendrites, columns and needles. As the riming process continues, the mass of frozen, accumulated cloud droplets eventually obscures the form of the original snow crystal, thereby giving rise to graupel.[4]
Graupel encasing and hiding a snow crystal from view
Rime on both ends of a columnar snow crystal
Graupel and avalanchesedit
Graupel commonly forms in high-altitude[quantify] climates and is both denser and more granular than ordinary snow, due to its rimed exterior. Macroscopically, graupel resembles small beads of polystyrene. The combination of density and low viscosity makes fresh layers of graupel unstable on slopes, and layers of 20–30 cm (8–12 in) or higher present a high risk of dangerous slab avalanches. In addition, thinner layers of graupel falling at low temperatures can act as ball bearings below subsequent falls of more naturally stable snow, rendering them also liable to avalanche or otherwise making surfaces slippery.[7] Graupel tends to compact and stabilise ("weld") approximately one or two days after falling, depending on the temperature and the properties of the graupel.[8]
Galleryedit
Snowflakes can turn into graupel
Almost graupel
Graupel in shape of snowflake
See alsoedit
Sleet – term variously used for frozen precipitation
^"What in the world is graupel?". KUSA.com. April 30, 2019. Retrieved 2022-05-16.
^ ab. U.S. Department of Agriculture Electron Microscopy Unit, Beltsville Agricultural Research Center. Archived from the original on 2017-07-11. Retrieved 2020-03-23.
^Chueh, Chih-Che; Wang, Pao K.; Hashino, Tempei (January 2018). "Numerical Study of Motion of Falling Conical Graupel". Atmospheric Research. 199: 82–92. doi:10.1016/j.atmosres.2017.09.008.
^. American Avalanche Association. Archived from the original on 2010-05-04.
External linksedit
Look up graupel in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Graupel.
Dictionariesedit
3 results for:graupel. Dictionary.com, accessed September 12, 2006.
. Merriam-Webster Online Dictionary, accessed September 12, 2006.
Weather glossariesedit
. The Weather Channel, accessed September 12, 2006.
All About Snow. National Snow and Ice Data Center (NSIDC), accessed September 12, 2006.
Terms used by meteorologists, forecasters, weather observers, and in weather forecasts. National Oceanic and Atmospheric Administration (NOAA), accessed September 12, 2006.
. Weather at About.com, accessed December 21, 2008.
January 01, 1970
graupel, german, ˈɡʁaʊpl, also, called, soft, hail, snow, pellets, precipitation, that, forms, when, supercooled, water, droplets, collected, freeze, falling, snowflakes, forming, balls, crisp, opaque, rime, pellets, morning, having, fallen, previous, distinct. Graupel ˈ ɡ r aʊ p el German ˈɡʁaʊpl also called soft hail or snow pellets 1 is precipitation that forms when supercooled water droplets in air are collected and freeze on falling snowflakes forming 2 5 mm 0 08 0 20 in balls of crisp opaque rime 2 Graupel pellets in morning having fallen the previous day Graupel is distinct from hail and ice pellets in both formation and appearance However both hail and graupel are common in thunderstorms with cumulonimbus clouds though graupel also falls in winter storms and at higher elevations as well 3 The METAR code for graupel is GS Contents 1 Formation 2 Microscopic structure 3 Graupel and avalanches 4 Gallery 5 See also 6 References 7 External links 7 1 Dictionaries 7 2 Weather glossariesFormation edit nbsp Falling graupel nbsp Conical graupel particle Under some atmospheric conditions snow crystals may encounter supercooled water droplets These droplets which have a diameter of about 10 mm 0 00039 in on average can exist in the liquid state at temperatures as low as 40 C 40 F far below the normal freezing point as long as above the homogeneous nucleation point of water Contact between a snow crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystal This process of crystal growth is known as accretion Crystals that exhibit frozen droplets on their surfaces are often referred to as rimed When this process continues so that the shape of the original snow crystal is no longer identifiable and has become ball like the resulting crystal is referred to as graupel 4 As graupel falls it often deforms into a conical shape This conical shape in turn determines which direction it falls and how far it travels as it falls Small graupel particles with a base diameter less than 1mm generally fall with the conical base down but if the particle is between 1mm and 3mm persistent oscillations around the center of the conical base appear and if larger than 3mm the graupel particle will start to tumble As the base diameter increases conical graupel particles generally further horizontally from where it initially fell 5 Graupel was formerly referred to by meteorologists as soft hail Graupel is distinguishable from true hail in both the shape and strength of the pellet and in some cases the circumstances in which it falls Ice from hail is formed in hard relatively uniform layers and usually falls only during thunderstorms Graupel forms fragile soft oblong crystals and falls in place of typical snowflakes in wintry mix situations often in concert with ice pellets However graupel does also occur in thunderstorms Graupel is also fragile enough that it will typically fall apart when pressed on 6 Microscopic structure editThe frozen droplets on the surface of rimed crystals are difficult to see even when zoomed in and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument However observations of snow crystals with a low temperature scanning electron microscope LT SEM clearly show frozen cloud droplets measuring up to 50 mm 0 002 in on the surface of the crystals The rime has been observed on all four basic forms of snow crystals including plates dendrites columns and needles As the riming process continues the mass of frozen accumulated cloud droplets eventually obscures the form of the original snow crystal thereby giving rise to graupel 4 nbsp Graupel encasing and hiding a snow crystal from view nbsp Rime on both ends of a columnar snow crystalGraupel and avalanches editGraupel commonly forms in high altitude quantify climates and is both denser and more granular than ordinary snow due to its rimed exterior Macroscopically graupel resembles small beads of polystyrene The combination of density and low viscosity makes fresh layers of graupel unstable on slopes and layers of 20 30 cm 8 12 in or higher present a high risk of dangerous slab avalanches In addition thinner layers of graupel falling at low temperatures can act as ball bearings below subsequent falls of more naturally stable snow rendering them also liable to avalanche or otherwise making surfaces slippery 7 Graupel tends to compact and stabilise weld approximately one or two days after falling depending on the temperature and the properties of the graupel 8 Gallery edit nbsp Snowflakes can turn into graupel nbsp Almost graupel nbsp Graupel in shape of snowflakeSee also editSleet term variously used for frozen precipitation Freezing rain Ice pelletsReferences edit Graupel Definition Merriam Webster Dictionary Merriam Webster Retrieved 15 Jan 2012 Glossary International Cloud Atlas World Meteorological Organization 2017 Retrieved 2019 09 03 What in the world is graupel KUSA com April 30 2019 Retrieved 2022 05 16 a b Rime and Graupel U S Department of Agriculture Electron Microscopy Unit Beltsville Agricultural Research Center Archived from the original on 2017 07 11 Retrieved 2020 03 23 Chueh Chih Che Wang Pao K Hashino Tempei January 2018 Numerical Study of Motion of Falling Conical Graupel Atmospheric Research 199 82 92 doi 10 1016 j atmosres 2017 09 008 Graupel What Is Graupel Archived 2012 02 16 at the Wayback Machine Weather Glossary G About com LaChapelle Edward R May 1966 The Relation of Crystal Riming to Avalanche Formation in New Snow Department of Atmospheric Sciences University of Washington Archived from the original on 2008 12 06 Graupel American Avalanche Association Archived from the original on 2010 05 04 External links edit nbsp Look up graupel in Wiktionary the free dictionary nbsp Wikimedia Commons has media related to Graupel Dictionaries edit 3 results for graupel Dictionary com accessed September 12 2006 Graupel Merriam Webster Online Dictionary accessed September 12 2006 Weather glossaries edit Weather Glossary G The Weather Channel accessed September 12 2006 All About Snow National Snow and Ice Data Center NSIDC accessed September 12 2006 Terms used by meteorologists forecasters weather observers and in weather forecasts National Oceanic and Atmospheric Administration NOAA accessed September 12 2006 About com Weather Glossary Weather at About com accessed December 21 2008 Retrieved from https en wikipedia org w index php title Graupel amp oldid 1215788280, wikipedia, wiki, book, books, library,
