AskDefine | Define troposphere

Dictionary Definition

troposphere n : the lowest atmospheric layer; from 4 to 11 miles high (depending on latitude)

User Contributed Dictionary

English

Etymology

From troposphère.

Noun

  1. The lower levels of the atmosphere extending from the earth's surface up to the tropopause. It is characterized by convective air movements and a large vertical temperature change.

Extensive Definition

  • ρ stands for density
  • z stands for height
  • p stands for pressure
  • R stands for the gas constant
  • T stands for temperature in kelvins
  • m stands for the molar mass
Since temperature in principle also depends on altitude, one needs a second equation to determine the pressure as a function of height, as discussed in the next section.

Temperature

The temperature of the troposphere generally decreases with altitude. The rate at which the temperature decreases, -dT/dz, is called the lapse rate. The reason for this decrease is as follows. When a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air parcel expands, it pushes on the air around it, doing work; but generally it does not gain heat in exchange from its environment, because its thermal conductivity is low (such a process is called adiabatic). Since the parcel does work and gains no heat, it loses energy, and so its temperature decreases. (The reverse, of course, will be true for a sinking parcel of air.)
p(z)T(z)^=constant
where \gamma is the heat capacity ratio (\gamma=7/5, for air). Combining with the equation for the pressure, one arrives at the dry adiabatic lapse rate,
\frac=- \frac \frac=-9.8^\mathrm/\mathrm
If the air contains water vapor, then cooling of the air can cause the water to condense, and the behavior is no longer that of an ideal gas. If the air is at the saturated vapor pressure, then the rate at which temperature drops with height is called the saturated adiabatic lapse rate. More generally, the actual rate at which the temperature drops with altitude is called the environmental lapse rate. In the troposphere, the average environmental lapse rate is a drop of about 6.5 °C for every 1 km (1000 meters) increase in height.
The environmental lapse rate (the actual rate at which temperature drops with height, dT/dz) is not usually equal to the adiabatic lapse rate (or correspondingly, dS/dz \ne 0). If the upper air is warmer than predicted by the adiabatic lapse rate (dS/dz > 0), then when a parcel of air rises and expands, it will arrive at the new height at a lower temperature than its surroundings. In this case, the air parcel is denser than its surroundings, so it sinks back to its original height, and the air is stable against being lifted. If, on the contrary, the upper air is cooler than predicted by the adiabatic lapse rate, then when the air parcel rises to its new height it will have a higher temperature and a lower density than its surroundings, and will continue to accelerate upward.
Temperatures decrease at middle latitudes from an average of 15°C at sea level to about -55°C at the beginning of the tropopause. At the poles, the troposphere is thinner and the temperature only decreases to -45°C, while at the equator the temperature at the top of the troposphere can reach -75°C.

Tropopause

The tropopause is the boundary region between the troposphere and the stratosphere.
Measuring the temperature change with height through the troposphere and the stratosphere identifies the location of the tropopause. In the troposphere, temperature decreases with altitude. In the stratosphere, however, the temperature remains constant for a while and then increases with altitude. The region of the atmosphere where the lapse rate changes from positive (in the troposphere) to negative (in the stratosphere), is defined as the tropopause. Thus, the tropopause is an inversion layer, and there is little mixing between the two layers of the atmosphere.

References

troposphere in Arabic: تروبوسفير
troposphere in Bosnian: Troposfera
troposphere in Bulgarian: Тропосфера
troposphere in Catalan: Troposfera
troposphere in Czech: Troposféra
troposphere in Danish: Troposfære
troposphere in German: Troposphäre
troposphere in Modern Greek (1453-): Τροπόσφαιρα
troposphere in Spanish: Troposfera
troposphere in Esperanto: Troposfero
troposphere in Basque: Troposfera
troposphere in French: Troposphère
troposphere in Galician: Troposfera
troposphere in Korean: 대류권
troposphere in Croatian: Troposfera
troposphere in Indonesian: Troposfer
troposphere in Interlingua (International Auxiliary Language Association): Troposphera
troposphere in Italian: Troposfera
troposphere in Hebrew: טרופוספירה
troposphere in Lithuanian: Troposfera
troposphere in Hungarian: Troposzféra
troposphere in Macedonian: Тропосфера
troposphere in Malay (macrolanguage): Troposfera
troposphere in Dutch: Troposfeer
troposphere in Japanese: 対流圏
troposphere in Norwegian: Troposfæren
troposphere in Norwegian Nynorsk: Troposfæren
troposphere in Polish: Troposfera
troposphere in Portuguese: Troposfera
troposphere in Russian: Тропосфера
troposphere in Sicilian: Trupusfera
troposphere in Slovak: Troposféra
troposphere in Serbian: Тропосфера
troposphere in Finnish: Troposfääri
troposphere in Swedish: Troposfär
troposphere in Vietnamese: Tầng đối lưu
troposphere in Turkish: Troposfer
troposphere in Ukrainian: Тропосфера
troposphere in Chinese: 对流层

Synonyms, Antonyms and Related Words

Appleton layer, CAT, F layer, Heaviside-Kennelly layer, Van Allen belt, aerospace, aerosphere, air hole, air pocket, airspace, belt, bump, ceiling, chemosphere, crosswind, empty space, favorable wind, fog, front, head wind, high-pressure area, hole, ionosphere, isothermal region, jetstream, layer, low-pressure area, lower atmosphere, outer atmosphere, overcast, photosphere, pocket, roughness, soup, space, stratosphere, stratum, substratosphere, tail wind, tropopause, trough, turbulence, upper atmosphere, visibility, visibility zero
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