Troposphere

The troposphere [ troposfɛ ː rə ] (from Greek τροπή trope " turn, change" and σφαίρα sphaira " ball " ) is the lowest layer of the atmosphere and part of the homosphere. The troposphere extends from the ground to the beginning of the stratosphere. The boundary between them is called the tropopause.

Its thickness is about 8 km at the poles (where it is up to 2 km lower in winter than in summer) and 18 km at the equator. In the troposphere, about 90 percent of the total air and almost all the water vapor in the Earth's atmosphere are included. Since playing the majority of the weather in it, one also speaks of the weather layer (or Advektionsschicht ) of the atmosphere.

Characteristics

The troposphere is heated only to a small extent by direct sun rays. Most of the heat is absorbed by the earth, so the air temperature on average by about 6.5 ° C per kilometer height decreases ( definition of standard atmosphere). This is called the vertical atmospheric temperature.

Specifically, the temperature decrease in trockenadiabatischen ( = cloudless ) sections amounts to 1 degree for every 100 meters ( dalr ), in moist -adiabatic ( clouds and fog rich ) space there are about 0.6 degrees per 100 meters ( SALR ). At the tropopause the temperature is about -75 ° C ( at the equator) to -45 ° C ( at the poles ). From this height the temperature initially the same ( isothermal process ) remains and then decreases in the stratosphere again ( inversion), in 50 km altitude it is reset to 0 ° C.

Because hot gases rise up within the troposphere and decrease cold, the air is mixed, the emergence of weather is possible. Due to the existing water vapor clouds are formed, rain is formed and the troposphere is purified of dissolved gases and solids. The tropopause is due to the inversion of a mixing limit dar. With the stratosphere, therefore, only a small air exchange takes place. All processes that influence the weather, take place in the troposphere.

Outline of the troposphere

The troposphere has the following layers:

• Bottom centimeters: laminar sublayer. If for microclimatic issues of particular interest because in this layer due to intense friction influence virtually no air movement occurs.
• Lowest about 2 meters: ground-level boundary layer, while violinist layer. A strong vertical wind speed increase and, especially at high temperatures, a strong decrease in temperature with height. The near-surface boundary layer is the habitat of humans, animals and mostly also the vegetation.
• Bottom 50 m: surface air layer also Prandtl layer. It is still the Erdoberflächeneinfluss of importance and there is a pronounced increase in wind speed with height instead ( due to weakening bottom friction ). A major part of the ground vegetation projects into this layer.
• Bottom approximately 0.5-2 km: planetary boundary layer, also called friction layer or Peplosphäre. In this outer layer, the influence of friction is expressed mainly in a change in wind direction with height, as a further vertical wind speed increase.
• In addition (to the tropopause ): clear coating or free atmosphere. It is relief friction substantially. In this layer, a large part of the flight route traffic passes.

According to another definition, the planetary boundary layer to ( almost) enough to the ground. It is then divided into a ground-based inner layer ( Prandtl layer less than 50 m) and an outer layer ( Ekman - layer, above 50 m). The Ekman layer is characterized by a wind shift and the increase of wind with height (see Ekman spiral).