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The troposphere is the lowest layer of the Earth's atmosphere; it starts at the planetary boundary layer, and is the layer in which most weather phenomena occur. The troposphere contains the boundary layer, and ranges in height from an average of 9 km (5.6 mi; 30,000 ft) at the poles, to 17 km (11 mi; 56,000 ft) at the Equator.
Atop the troposphere is the tropopause, which is the functional atmospheric border that demarcates the troposphere from the stratosphere. As such, because the tropopause is an inversion layer in which air-temperature increases with altitude, the temperature of the tropopause remains constant. [2] The layer has the largest concentration of nitrogen.
All air entering the stratosphere must pass through the tropopause, the temperature minimum that divides the troposphere and stratosphere. The rising air is literally freeze dried; the stratosphere is a very dry place. The top of the stratosphere is called the stratopause, above which the temperature decreases with height.
Because convection is available to transfer heat within the atmosphere, the lapse rate in the troposphere is reduced to around 6.5 °C/km [8] and the greenhouse effect is reduced to a point where Earth has its observed surface temperature of around 288 K (15 °C; 59 °F).
The thermosphere (or the upper atmosphere) is the height region above 85 kilometres (53 mi), while the region between the tropopause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near an altitude of 45 kilometres (28 mi) and causes the ozone layer.
Thermals are caused by local differences in temperature, pressure, or impurity concentration in the vertical. Temperature differences can cause air currents because warmer air is less dense than cooler air, causing the warmer air to appear "lighter." Thus, if the warm air is under the cool air, air currents will form as they exchange places.
In the stratosphere, the temperature increases with altitude, and the stratopause is the region where a maximum in the temperature occurs. This atmospheric feature is not exclusive to Earth, but also occurs on any other planet or moon with an atmosphere . [ 1 ]
Temperature decreases with altitude starting at sea level, but variations in this trend begin above 11 km, where the temperature stabilizes over a large vertical distance through the rest of the troposphere. In the stratosphere, starting above about 20 km, the temperature increases with height, due to heating within the ozone layer caused by ...