Snow

of these articles is occupied with snow as precipitation. For a description of the novel of the same name of Orhan Pamuk see snow (novel).
Schneefall in der Eifel (2006)
Snow in the Eifel (2006)
Schneetreiben before the synagog in Dresden (2005)

snow is a precipitation, thatof fine ice crystals consists.


Table of contents

crystallization

close-up with electron microscope

snow develops, if in the clouds finest droplets undercooled themselves water at crystallization germs (for example a dust particle) deposit and freeze there. This process setshowever usually only at temperatures under -10 °C, whereby still to -40 °C also liquid water exists. The ice crystals, less than 0.1 mm largely, developing thereby, fall by increasing weight downward and grow by the differencethe steam pressure between ice and undercooled water further on. Also the water vapour contained in air resublimiert, changes thus directly into ice and contributes thereby to the crystal growth. The well-known hexagonal forms are formed. Because of thatspecial structure of the water molecules thereby only angles of 60° are and/or. 120° possible.

The different basic forms of the snow crystals hang sechsarmige dendrites ( stars) from the temperature – at lower temperatures are formed panels or prisms , at higher temperatures. Alsothe air humidity affects the crystal growth.

If a high thermionics prevails, then the crystals move several times vertically by the atmosphere, whereby they are partly melted and to crystallize again again to be able. Thus the regularity of the crystals is broken through and it to formitself complex combinations of the basic forms out. They do not exhibit astonishing high form variety, so that landläufig one states, it would give two identical snow crystals. Over 6.000 different crystalline forms 1962 by Bentley and Humphreys were counted. If snow crystals form, risesin the cloud also, because when freezing the crystals warmth deliver the temperature.

Likewise astonishing like the observed form variety their pronounced symmetry is, snow crystals the high self similarity lends and it for an advantages example of fraktalen geometryto become left (cook curve). Different branchings grow in copy always in the same way and obviously with similar speed, even if their points, at which they continue to grow, apart lie often several millimeters. A possible attempt at explanation, withoutAcceptance of a reciprocal effect over this distance away gets along, exists in the reference that the growth conditions in different comparable germ places at the points are surely always quite similar at same times. A detailed representation to this topic is in oneat the conclusion of the article indicated Web left.

The largest complexity of the snow crystals shows up with a high air humidity, since growing makes these also still filigraneren structures possible. With less than -30 °C it does not snow usually any longer, there air thento drying is, in order to form still snow crystals. However perhaps clouds with snow crystals already eye-formed can be advanced by advection. Such snow clouds are in principle dark, because the more largely the cloud, the more largely is also the humidity. Thusthe cloud fewer light lets through and becomes darker.

flakes

flakes
photo: Wilson Bentley

is the air temperature close because of the freezing point, then the individual ice crystals become throughsmall water drops stuck together with one another and it develop to a cotton ball reminding flakes. In strong showers it can snow however also at temperatures around 5 degrees or some more over it. On the other hand it occurs that also with under zero degree of rainfalls, then as freezing rains. For this effect in some media the misleading term lightning ice is used (with the meteorological phenomenon lightning has freezing rain however nothing to do). These components hang of structure and layering stability of the upper and lowerAir layers, of geographical influences as well as weather elements like for example cool air drops off. At low temperatures only very small Flöckchen, the Schneegriesel in such a way specified forms.

Flakes contain air up to 95%. Air provides for a small densitythe flake, why it falls down with speeds from approximately 0.2 m/s, thus relatively slowly.

Also the white color of the snow lies likewise in the fact justified that the snow consists of ice crystals. Each individual crystal actual such as ice as such - transparency; the light of all visible wavelengths is reflected and strewn at the boundary surfaces between the ice crystals and surrounding air. A sufficiently large accumulation of ice crystals with coincidental situation relationship leads to each other thereby altogether with vague reflection; Snow appearstherefore knows. A similar effect is to be observed for example also with salt with the comparison powder versus larger crystal.

The largest flake ever seen had a diameter of twelve centimeters. Usually there is however only five millimeters with a weight of0.004 gram. The more highly the temperature will become the higher, the flakes. If it becomes warmer, the crystals melt and stick together to large flakes.

A flake sinks with a speed of 0,9 km/h on earth (to the comparison: Rain falls also36 km/h). If a flake falls on water, then it produces due to into their enclosed bubbles a shrill high clay/tone with a frequency from 50 to 200 kilohertz, which is unpleasant for humans inaudibly, but but for many fish.

thaw

Ade Schnee!
Ade snow!

Snow melts at temperatures over the melting point of the water, thus with 0 °C, in addition, by exposure to the sun. Here also sublimation is possible, i.e. a direct phase transition from snow to water vapour without thatSnow would melt. The drier air is, the less melts the snow, since the remaining snow is cooled by sublimation cold weather.

Because of the high air content also the snow solidified at the soil the planar inundations remain when melting the snow coverageout. The water, which is removed by rivers, can lead however in the river valleys to the well-known spring inundations, because the snow from a very large surface thaws and collects themselves in the relatively narrow Flussbetten as water.

Kinds of snow

gives different criteria, on the basis whose one can divide the snow.

age

Verschneite Landschaft
snow-covered landscape
snow and plants
  • new-fallen snow is freshly pleased snow, which is not older than three days. The ice crystals are still finely branched alsosharpen points/teeth.
  • Old snow lies already at least three days. Are with temperature and pressure the crystals less strongly branch out and more rounded off.
  • Harsch is old snow, which by melts and freezing at the surface trained a firm, frozen layer, during the snowamong them remains powder-like. Depending upon thickness of the hard layer the Harschdecke can be broken through by easy auxiliary loads.See also: Harscheisen
  • Firnschnee (short Firn) is at least one year old. Its density is higher (over 0,6 g/cm ³). The fine ice crystalsby recurring thawing out and freezing into larger ice breaking into merged. From the Firnschnee glaciers can develop in the run the time. As Firn one in addition, the superficial, call themselves soft snow layer, in spring by sun exposure and high air temperatures upforms (at the preceding night frozen) for a Harschfläche. One speaks in this case of the fact that a slope “auffirnt”.See also: Firnfeld

humidity

  • powder snow is dry snow, which does not stick also under pressure. Its density is below 60kg/m ³. In the American Rocky Mountains it is called also Champagner Powder.
  • Damp snow sticks it under pressure together and is suitable therefore particularly for Schneebälle and Schneemänner, can however no water be pressed out. It is called also sticking snow, becauseit together-sticks.
  • Wet snow or Sulz (also: Sulzschnee - Adj. sulzig) is very heavy and wet, he sticks likewise together and one can water out press.
  • Putrid snow is a mixture made of water and larger snow breaking into, which do not hold together any longer well (Slush).
  • At the Temperaturgrenze (transition in the height or with weather reversals) snow rain , i.e. a mixture made of snow and rain fall.

color

  • Blutschnee is usually by a mass development of blood algae (e.g. Chlamydomonas nivalis) or urine sparkling wines, in addition, by coming down reddish dust masses from the seeing era reddish discoloured snow.
  • One by kryophile (coolingloving) snow algae caused green colouring was likewise discovered in glaciers and arctic snow surfaces.

occurrence and origin

  • flight snowis very fine snow, which penetrates by the effect of the wind into houses.
  • Snow bank: one is by wind transport caused accumulation of snow, their height over the actual amount of precipitation to clearly find can
  • art snow is artificially produced snow.

meaning

effects on the climate and the living world

in areas with a well trained Schneedecke by the brighter soil color more radiant heat back into the atmosphere is reflected and the soil takes up accordingly less. Not least must to Schmelzvorgang of the snow the heat of fusion in such a way specified to be applied, which is then lost as heat energy. By enclosed air snow forms also a good heat insulator, which protects plants under the Schneedecke against sharp frost wind.

role for thatHumans

Schneeballschlacht around 1400 (master Venceslao: January, Detail)

for humans plays the snow apart from its aesthetic meaning in its role as metaphor for the winter economically particularly in the leisure activities and concomitantly for the tourism an importantRole (see also winter sports). Particularly with children are building Schneemännern and delivering Schneeballschlachten like.

A large danger particularly for winter sportsmen proceeds from avalanches, those in extreme cases in addition, already wholeVillages to the victim please are.

Also by smoothness on traffic routes snow represents a danger and leads pretty often to a complete collapse of the flow of traffic. After strong snows roads are often only passable by tire chains. Winter clearing services are assigned the removal of the snow, but those is evacuation of snow by means of snow plough, snow milling cutter or other aids also for private people one far spreads occupation during the winter months.

Where the snow falls in natural way not or not sufficiently, one managesitself with art snow, which is produced by snow cannons.

snow research

history

the strictly hexagonal structure of flakes was in the Empire of China already at least since that 2. Century v. Chr. admits. In the evening country noticedthis characteristic for the first time the English mathematician Thomas Harriot in the year 1591, which did not publish its observation however. Work over formula-much-fall the snow crystals are well-known also from Johannes Kepler and René the Descartes, but first systematic investigations undertook only Ukichiro Nakaya, the 1936 as the first synthetic flakes to manufacture could do and this 1954 in over 200 different types categorized.

snow measurements

measurements of the snow quantity are accomplished with the help of usual rain-gauges, with those to the protection against blowing of Schneekreuzeare attached. The power of the snow surface is determined with snow levels or snow probes. The increase can be measured also with ultrasonic. With the German weather service snow cover power and the new-fallen snow height are measured daily around 7:30 clock of legal time.

The Wasseranteil (water equivalenta Schneedecke) and the snow density have meaning for the climatology and hydrology. Also the snow border is an important climatological characteristic. The snow border separates snow-covered and areas free of snow.

see also

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Wiktionary: Snow - word origin, synonyms and translations
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