Alpine climate

For the climate of the mountains named the "Alps", see Climate of the Alps.
White Mountain, an alpine environment at 4,300 metres (14,000 ft) in California

Alpine climate is the average weather (climate) for the regions above the tree line. This climate is also referred to as a mountain climate or highland climate.

In the Köppen climate classification, the alpine climate is part of "Group E", along with the polar climate, where no month has a mean temperature higher than 10 °C (50 °F).[1] Certain highland climates can also fit under the hemiboreal climate or semi-arid climate groups of climate classification.

Description

The temperature profile of the atmosphere is a result of an interaction between radiation and convection. Sunlight in the visible spectrum hits the ground and heats it. The ground then heats the air at the surface. If radiation were the only way to transfer heat from the ground to space, the greenhouse effect of gases in the atmosphere would keep the ground at roughly 333 K (140 °F), and the temperature would decay exponentially with height.[2]

However, when air is hot, it tends to expand, which lowers its density. Thus, hot air tends to rise and transfer heat upward. This is the process of convection. Convection comes to equilibrium when a parcel at air at a given altitude has the same density as its surroundings. Air is a poor conductor of heat, so a parcel of air will rise and fall without exchanging heat. This is known as an adiabatic process, which has a characteristic pressure-temperature curve. As the pressure gets lower, the temperature decreases. The rate of decrease of temperature with elevation is known as the adiabatic lapse rate, which is approximately 9.8 °C per kilometer (or 5.4 °F per 1000 feet) of altitude.[2]

Note that the presence of water in the atmosphere complicates the process of convection. Water vapor contains latent heat of vaporization. As air rises and cools, it eventually becomes saturated and cannot hold its quantity of water vapor. The water vapor condenses (forming clouds), and releases heat, which changes the lapse rate from the dry adiabatic lapse rate to the moist adiabatic lapse rate (5.5 °C per kilometer or 3&nbsp°F per 1000 feet[3] The actual lapse rate, called the environmental lapse rate, is not constant (it can fluctuate throughout the day or seasonally and also regionally), but a normal lapse rate is 5.5 °C per 1,000 m (3.57 °F per 1,000 ft).[4][5] Therefore, moving up 100 metres (330 ft) on a mountain is roughly equivalent to moving 80 kilometres (45 miles or 0.75° of latitude) towards the pole.[6] This relationship is only approximate, however, since local factors, such as proximity to oceans, can drastically modify the climate.[7] As the altitude increases, the main form of precipitation becomes snow and the winds increase. The temperature continues to drop until the tropopause, at 11,000 metres (36,000 ft), where it does not decrease further. However, this is higher than the highest summit.

Distribution

Although this climate classification only covers a small portion of the Earth's surface, alpine climates are widely distributed. The altitude where alpine climate (and the tree line) occurs varies dramatically by latitude. For example, at 68°N in Sweden, alpine climate occurs as low as 650 metres (2,130 ft),[8] while on Mount Kilimanjaro in Africa, alpine and the tree line occurs at 3,950 metres (12,960 ft).[8]

The Sierra Nevada, the Cascade Mountains, the Rocky Mountains, the Appalachian Mountains, the Alps, the Snowy Mountains in Australia, the Spanish Pyrenees, Cantabrian Mountains and Sierra Nevada, the Andes, the Himalayas, the Tibetan Plateau, Gansu China, Qinghai, the Eastern Highlands of Africa, high elevations in the Atlas Mountains and the central parts of Borneo and New Guinea are examples of regions that have alpine climates. The mountain climate in the Northern Andes is particularly known for the notion of four zones of elevation:

In mountainous areas with an alpine climate, the dominant biome is alpine tundra.

See also

References

  1. ↑ McKnight, Tom L; Hess, Darrel (2000). "Climate Zones and Types: The Köppen System". Physical Geography: A Landscape Appreciation. Upper Saddle River, New Jersey: Prentice Hall. pp. 235–7. ISBN 0-13-020263-0.
  2. 1 2 Goody, Richard M.; Walker, James C.G. (1972). "Atmospheric Temperatures" (PDF). Atmospheres. Prentice-Hall.
  3. ↑ "Dry Adibatic Lapse Rate". tpub.com. Retrieved 2016-05-02.
  4. ↑ "Adiabatic Lapse Rate". Goldbook. IUPAC.
  5. ↑ Dommasch, Daniel O. (1961). Airplane Aerodynamics (3rd ed.). Pitman Publishing Co. p. 22.
  6. ↑ "Mountain Environments" (PDF). United Nations Environment Programme World Conservation Monitoring Centre. Archived from the original (PDF) on 2011-08-25.
  7. ↑ "Factors affecting climate". The United Kingdom Environmental Change Network. Archived from the original on 2011-07-16.
  8. 1 2 Körner, Ch (1998). "A re-assessment of high elevation treeline positions and their explanation" (PDF). Oecologia 115 (4): 445–459. doi:10.1007/s004420050540.
This article is issued from Wikipedia - version of the Tuesday, May 03, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.