Snow line
Snow line refers to two different height limits in the mountains , above which snow remains on the ground.
- Mostly the climatic snow line is meant: This is the (largely) static dividing line between year - round snow-covered and temporarily snow-free areas. It is mainly climatic due to the geographical location . ie, the latitude and the strength of the solar radiation determined by exposure (sun or shadow slope) and the degree of cloudiness . In damp, cool, cloudy maritime climates , for example, it can still be at annual mean temperatures of +4 to 5 ° C, while it needs at least –8 to –10 ° C in a dry, cloudless continental climate . The Nivale altitude level is located above the climatic snow line .
- The current (also temporary ) snow line is more rarely meant: This is the changing current dividing line between snow-covered and snow-free areas. In the thaw, it is below the snow line . The location of the current snow line is therefore weather-related .
The limit of snowfall is the weather-related height up to which precipitation occurs in the form of snow.
Climatic snow line
Snow limits depend on the climate and geographical latitude. While the climatic snow line in the tropical zone of the earth is over 6000 m, the snow in middle latitudes already lies at 3000 m. In the Arctic and Antarctic the snow line is insignificantly above sea level .
A distinction can be made between two climatic snow limits:
- The firn border (the actual climatic snow line ) represents the border to the closed snow cover. This means that the deposited snow no longer melts and becomes firn due to the thawing in the summer half-year .
- The orographical snow line , on the other hand, indicates how far down the valley individual patches of snow can stay in sheltered or shady areas throughout the summer (remains of old wood, dead ice ).
The steeper the mountain range , the greater the difference between the orographical and firn borders , because the differences in local weather usually increase with the slope of the terrain.
Equilibrium line
The average altitude of the firn border on glaciers in the high mountains approximately coincides with the border between the nutrient and consumption area - the so-called equilibrium line . Above this limit, which is just below 3000 m in the Alps , almost every snowfall leads to firn - and as a result of the metamorphosis to ice formation , below the snowline the snow melts in summer. "Snow-free" ( aper ) does not mean " ice-free": Glaciers can also dry out - that is, the snow cover melts and the old ice is exposed.
Rise in the snow line as a result of global warming
As a result of global warming , the snow line has risen in recent years, and the glaciers below this limit have melted. Since the temperature in the lower atmosphere decreases with an average of 6 ° C per kilometer upwards, an average temperature increase of 2 ° C means an increase in the snow line by around 300 meters.
Some data on the climatic snow line
The firn or climatic snow line depends - as indicated above - not only on the geographical latitude, but also on the regional microclimate . It is determined, among other things, by the distance to the coast ( marine temperature compensation), the amount of precipitation , the course of warm ocean currents and the shape of the terrain .
The table below gives some average values and the latitudes:
region | B (°) | H (m) | climatological factors |
---|---|---|---|
Spitzbergen (archipelago) | 78 | 300- 600 | |
Scandinavia at | 67 | 1000-1500 | Gulf Stream |
Iceland | 65 | 700-1100 | Gulf Stream |
Scandinavia at | 62 | 1200-2200 | |
Alps (north side) | 48 | 2500-2800 | North Atlantic traffic jam |
Central Alps | 47 | 2900-3200 | |
Alps (south side) | 46 | 2700-2800 | more uniform climate ( Mediterranean climate ) |
Pyrenees | 43 | 2600-2900 | see. New Zealand at −43 |
Caucasus | 43 | 2700-3800 | Continental climate |
Karakoram | 36 | 5400-5800 | Continental climate |
Transhimalaya | 30-33 | 6300-6500 | Continental climate |
Himalayas | 30th | 4800-6000 | Shadowing |
Kenya | 0 | 4600-4700 | Tropics |
New Guinea | −2 | 4600-4700 | hardly any seasons |
Andes in Ecuador | −2 | 4800-5000 | Tropics |
Kilimanjaro | −3 | 5500-5600 | Tropics |
Andes in Chile | −27 | 5800-6500 | mild winter temperatures |
New Zealand | −43 | 1600-2700 | harsher southern climate, see Ecliptic |
fire land | −54 | 800-1300 | |
Antarctic Peninsula | −70 | 0- 400 |
See also
- Snow day - as a measure of time (also with several special definitions)
- Ice line in interplanetary space
Web links
- Депрессия снеговой линии , on snowline depression in the Russian language Wikipedia
Individual evidence
- ↑ Dieter Heinrich, Manfred Hergt: Atlas for ecology. Deutscher Taschenbuch Verlag, Munich 1990, ISBN 3-423-03228-6 . P. 97.
- ↑ averaged from Brockhaus -Multimedial 2007