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Concept
Climat alpin
Résumé
Alpine climate is the typical weather (climate) for elevations above the tree line, where trees fail to grow due to cold. This climate is also referred to as a mountain climate or highland climate.
There are multiple definitions of alpine climate.
In the Köppen climate classification, the alpine and mountain climates are part of group E, along with the polar climate, where no month has a mean temperature higher than .
According to the Holdridge life zone system, there are two mountain climates which prevent tree growth :
a) the alpine climate,
which occurs when the mean biotemperature of a location is between . The alpine climate in Holdridge system is roughly equivalent to the warmest tundra climates (ET) in the Köppen system.
b) the alvar climate, the coldest mountain climate since the biotemperature is between 0 °C and 1.5 °C (biotemperature can never be below 0 °C). It corresponds more or less to the coldest tundra climates and to the ice cap climates (EF) as well.
Holdrige reasoned that plants net primary productivity ceases with plants becoming dormant at temperatures below and above . Therefore, he defined biotemperature as the mean of all temperatures but with all temperatures below freezing and above 30 °C adjusted to 0 °C; that is, the sum of temperatures not adjusted is divided by the number of all temperatures (including both adjusted and non-adjusted ones).
The variability of the alpine climate throughout the year depends on the latitude of the location. For tropical oceanic locations, such as the summit of Mauna Loa, the temperature is roughly constant throughout the year. For mid-latitude locations, such as Mount Washington in New Hampshire, the temperature varies seasonally, but never gets very warm.
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.
Source officielle
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