Alpine climate

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White Mountain, an alpine environment at 4,300 metres (14,000 ft) above sea level in California White Mountain CA.JPG
White Mountain, an alpine environment at 4,300 metres (14,000 ft) above sea level in California

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

Contents

Definition

There are multiple definitions of alpine climate.

One simple definition is the climate which causes trees to fail to grow due to cold.

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 10 °C (50 °F). [1]

According to the Holdridge life zone system, there are two mountain climates which prevent tree growth :

a) the alpine climate proper which occurs when the mean biotemperature of a location is between 1.5 and 3 °C (34.7 and 37.4 °F). 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 0 °C (32 °F) and above 30 °C (86 °F). [2] 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).

Cause

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 (60 °C; 140 °F), and the temperature would decay exponentially with height. [3]

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 of 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. [3]

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 kilometre or 3 °F per 1000 feet). [4] 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). [5] [6] Therefore, moving up 100 metres (330 ft) on a mountain is roughly equivalent to moving 80 kilometres (50 miles or 0.75° of latitude) towards the pole. [7] This relationship is only approximate, however, since local factors, such as proximity to oceans, can drastically modify the climate. [8] 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. 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. They are present in the Himalayas, the Tibetan Plateau, Gansu, Qinghai, the Alps, the Pyrenees, the Cantabrian Mountains and the Sierra Nevada in Eurasia, the Andes in South America, the Sierra Nevada, the Cascade Mountains, the Rocky Mountains, the Appalachian Mountains, and the Trans-Mexican volcanic belt in North America, the Southern Alps in New Zealand, the Snowy Mountains in Australia, high elevations in the Atlas Mountains and the Eastern Highlands of Africa, and the central parts of Borneo and New Guinea and the summits of Mount Pico in the Atlantic [9] and Mauna Loa in the Pacific.

The lowest altitude of alpine climate varies dramatically by latitude. If alpine climate is defined by the tree line, then it occurs as low as 650 metres (2,130 ft) at 68°N in Sweden, [10] while on Mount Kilimanjaro in Africa, the tree line is at 3,950 metres (12,960 ft). [10]

Monthly variability

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, elev. 13,679 ft (4,169 m), the temperature is roughly constant throughout the year:

Climate data for Mauna Loa slope observatory (1961–1990), extremes 1955–2012
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Record high °F (°C)67
(19)
85
(29)
65
(18)
67
(19)
68
(20)
71
(22)
70
(21)
68
(20)
67
(19)
66
(19)
65
(18)
67
(19)
85
(29)
Average high °F (°C)49.8
(9.9)
49.6
(9.8)
50.2
(10.1)
51.8
(11.0)
53.9
(12.2)
57.2
(14.0)
56.4
(13.6)
56.3
(13.5)
55.8
(13.2)
54.7
(12.6)
52.6
(11.4)
50.6
(10.3)
53.2
(11.8)
Average low °F (°C)33.3
(0.7)
32.9
(0.5)
33.2
(0.7)
34.6
(1.4)
36.6
(2.6)
39.4
(4.1)
38.8
(3.8)
38.9
(3.8)
38.5
(3.6)
37.8
(3.2)
36.2
(2.3)
34.3
(1.3)
36.2
(2.3)
Record low °F (°C)19
(−7)
18
(−8)
20
(−7)
24
(−4)
27
(−3)
28
(−2)
26
(−3)
28
(−2)
29
(−2)
27
(−3)
25
(−4)
22
(−6)
18
(−8)
Average precipitation inches (mm)2.3
(58)
1.5
(38)
1.7
(43)
1.3
(33)
1.0
(25)
0.5
(13)
1.1
(28)
1.5
(38)
1.3
(33)
1.1
(28)
1.7
(43)
2.0
(51)
17
(431)
Average snowfall inches (cm)0.0
(0.0)
1.0
(2.5)
0.3
(0.76)
1.3
(3.3)
0.0
(0.0)
0.0
(0.0)
0.0
(0.0)
0.0
(0.0)
0.0
(0.0)
0.0
(0.0)
0.0
(0.0)
1.0
(2.5)
3.6
(9.06)
Average precipitation days (≥ 0.01 inch)45654345555455
Source: NOAA, [11] WRCC [12]

For mid-latitude locations, such as Mount Washington in New Hampshire, the temperature varies seasonally, but never gets very warm:

Climate data for Mount Washington (New Hampshire), elev. 6,267 ft (1,910.2 m) near the summit
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Record high °F (°C)48
(9)
43
(6)
54
(12)
60
(16)
66
(19)
72
(22)
71
(22)
72
(22)
69
(21)
62
(17)
52
(11)
47
(8)
72
(22)
Average high °F (°C)13.6
(−10.2)
14.7
(−9.6)
20.7
(−6.3)
30.4
(−0.9)
41.3
(5.2)
50.4
(10.2)
54.1
(12.3)
53.3
(11.8)
47.1
(8.4)
36.4
(2.4)
28.1
(−2.2)
18.4
(−7.6)
34.0
(1.1)
Daily mean °F (°C)4.8
(−15.1)
6.2
(−14.3)
12.9
(−10.6)
23.9
(−4.5)
35.6
(2.0)
45.0
(7.2)
49.1
(9.5)
48.2
(9.0)
41.6
(5.3)
30.2
(−1.0)
20.7
(−6.3)
10.1
(−12.2)
27.4
(−2.6)
Average low °F (°C)−4.1
(−20.1)
−2.4
(−19.1)
5.0
(−15.0)
17.4
(−8.1)
29.8
(−1.2)
39.5
(4.2)
44.0
(6.7)
43.0
(6.1)
36.1
(2.3)
24.0
(−4.4)
13.3
(−10.4)
1.7
(−16.8)
20.6
(−6.3)
Record low °F (°C)−47
(−44)
−46
(−43)
−38
(−39)
−20
(−29)
−2
(−19)
8
(−13)
24
(−4)
20
(−7)
9
(−13)
−5
(−21)
−20
(−29)
−46
(−43)
−47
(−44)
Average precipitation inches (mm)6.44
(164)
6.77
(172)
7.67
(195)
7.44
(189)
8.18
(208)
8.40
(213)
8.77
(223)
8.32
(211)
8.03
(204)
9.27
(235)
9.85
(250)
7.73
(196)
96.87
(2,460)
Average snowfall inches (cm)44.0
(112)
40.1
(102)
45.1
(115)
35.6
(90)
12.2
(31)
1.0
(2.5)
0.0
(0.0)
0.1
(0.25)
2.2
(5.6)
17.6
(45)
37.8
(96)
45.5
(116)
281.2
(714)
Average precipitation days (≥ 0.01 in)19.717.919.017.417.416.816.515.213.916.819.120.7210.4
Average snowy days (≥ 0.1 in)19.317.316.613.16.40.90.10.21.79.114.619.2118.5
Mean monthly sunshine hours 92.0106.9127.6143.2171.3151.3145.0130.5127.2127.182.483.11,487.6
Percent possible sunshine 32363435373331303437293033
Source 1: NOAA (normals 1981–2010, sun 1961–1990) [13] [14] [15]
Source 2: extremes 1933–present [16] [17]

See also

Related Research Articles

Greenhouse effect Atmosopheric phenomenon

The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.

Mountain A large landform that rises fairly steeply above the surrounding land over a limited area

A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at least 300 metres above the surrounding land. A few mountains are isolated summits, but most occur in mountain ranges.

Troposphere The lowest layer of Earths atmosphere

The troposphere is the lowest layer of Earth's atmosphere, and is also where nearly all weather conditions take place. It contains 75% of the atmosphere's mass and 99% of the total mass of water vapour and aerosols. The average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, and 6 km in the polar regions in winter. The total average height of the troposphere is 13 km.

Cumulus cloud Genus of clouds, low-level cloud

Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin cumulo-, meaning heap or pile. Cumulus clouds are low-level clouds, generally less than 2,000 m (6,600 ft) in altitude unless they are the more vertical cumulus congestus form. Cumulus clouds may appear by themselves, in lines, or in clusters.

Inversion (meteorology) Deviation from the normal change of an atmospheric property with altitude

In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to an inversion of the air temperature lapse rate, in which case it is called a temperature inversion. Normally, air temperature decreases with an increase in altitude, but during an inversion the typical temperature profile with altitude is inverted: warmer air is held above cooler air.

Altitude or height is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context. Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.

Water vapor Gaseous phase of water

Water vapor, water vapour or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Water vapor is transparent, like most constituents of the atmosphere. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation. It is less dense than most of the other constituents of air and triggers convection currents that can lead to clouds.

Alpine tundra Biome found at high altitudes

Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets lower until it reaches sea level, and alpine tundra merges with polar tundra.

Lapse rate

The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. Lapse rate arises from the word lapse, in the sense of a gradual fall. In dry air, the adiabatic lapse rate is 9.8 °C/km.

Equivalent potential temperature, commonly referred to as theta-e, is a quantity that is conserved during changes to an air parcel's pressure, even if water vapor condenses during that pressure change. It is therefore more conserved than the ordinary potential temperature, which remains constant only for unsaturated vertical motions.

International Standard Atmosphere Atmospheric model

The International Standard Atmosphere (ISA) is a static atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations. It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes, plus some formulas by which those values were derived. The International Organization for Standardization (ISO) publishes the ISA as an international standard, ISO 2533:1975. Other standards organizations, such as the International Civil Aviation Organization (ICAO) and the United States Government, publish extensions or subsets of the same atmospheric model under their own standards-making authority.

Convective instability

In meteorology, convective instability or stability of an air mass refers to its ability to resist vertical motion. A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear. In an unstable atmosphere, vertical air movements tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence, extensive vertical clouds, and severe weather such as thunderstorms.

Level of free convection

The level of free convection (LFC) is the altitude in the atmosphere where the temperature of the environment decreases faster than the moist adiabatic lapse rate of a saturated air parcel at the same level.

Lifted condensation level

The lifted condensation level or lifting condensation level (LCL) is formally defined as the height at which the relative humidity (RH) of an air parcel will reach 100% with respect to liquid water when it is cooled by dry adiabatic lifting. The RH of air increases when it is cooled, since the amount of water vapor in the air remains constant, while the saturation vapor pressure decreases almost exponentially with decreasing temperature. If the air parcel is lifting further beyond the LCL, water vapor in the air parcel will begin condensing, forming cloud droplets. The LCL is a good approximation of the height of the cloud base which will be observed on days when air is lifted mechanically from the surface to the cloud base.

Atmospheric thermodynamics is the study of heat-to-work transformations that take place in the earth's atmosphere and manifest as weather or climate. Atmospheric thermodynamics use the laws of classical thermodynamics, to describe and explain such phenomena as the properties of moist air, the formation of clouds, atmospheric convection, boundary layer meteorology, and vertical instabilities in the atmosphere. Atmospheric thermodynamic diagrams are used as tools in the forecasting of storm development. Atmospheric thermodynamics forms a basis for cloud microphysics and convection parameterizations used in numerical weather models and is used in many climate considerations, including convective-equilibrium climate models.

The convective condensation level (CCL) represents the height where an air parcel becomes saturated when heated from below and lifted adiabatically due to buoyancy.

Atmospheric convection Atmospheric phenomenon

Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to increased winds, cumulus cloud development, and decreased surface dew points. Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.

Atmospheric instability Condition where the Earths atmosphere is generally considered to be unstable

Atmospheric instability is a condition where the Earth's atmosphere is generally considered to be unstable and as a result the weather is subjected to a high degree of variability through distance and time. Atmospheric stability is a measure of the atmosphere's tendency to discourage or deter vertical motion, and vertical motion is directly correlated to different types of weather systems and their severity. In unstable conditions, a lifted thing, such as a parcel of air will be warmer than the surrounding air at altitude. Because it is warmer, it is less dense and is prone to further ascent.

Representations of the atmospheric boundary layer in global climate models play a role in simulations of past, present, and future climates. Representing the atmospheric boundary layer (ABL) within global climate models (GCMs) are difficult due to differences in surface type, scale mismatch between physical processes affecting the ABL and scales at which GCMs are run, and difficulties in measuring different physical processes within the ABL. Various parameterization techniques described below attempt to address the difficulty in ABL representations within GCMs.

Glossary of meteorology List of definitions of terms and concepts commonly used in meteorology

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.

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