Lapse rate
It varies with the temperature and pressure of the parcel and is often in the range 3.6 to 9.2 °C/km (2 to 5 °F/1000 ft), as obtained from the International Civil Aviation Organization (ICAO).
The environmental lapse rate is the decrease in temperature of air with altitude for a specific time and place (see below).
Lapse rate corresponds to the vertical component of the spatial gradient of temperature.
Although this concept is most often applied to the Earth's troposphere, it can be extended to any gravitationally supported parcel of gas.
The ELR is forced towards the adiabatic lapse rate whenever air is moving vertically.
As an average, the International Civil Aviation Organization (ICAO) defines an international standard atmosphere (ISA) with a temperature lapse rate of 6.50 °C/km[7] (3.56 °F or 1.98 °C/1,000 ft) from sea level to 11 km (36,090 ft or 6.8 mi).
Unlike the idealized ISA, the temperature of the actual atmosphere does not always fall at a uniform rate with height.
[10][11]: 387 The air is radiatively cooled by greenhouse gases (water vapor, carbon dioxide, etc.)
Also, intra-atmospheric radiative heat transfer is relatively slow and so is negligible for moving air.
Since the upward-moving and expanding parcel does work but gains no heat, it loses internal energy so that its temperature decreases.
Downward-moving and contracting air has work done on it, so it gains internal energy and its temperature increases.
Energy transport in the atmosphere is more complex than the interaction between radiation and dry convection.
The water cycle (including evaporation, condensation, precipitation) transports latent heat and affects atmospheric humidity levels, significantly influencing the temperature profile, as described below.
The following calculations derive the temperature as a function of altitude for a packet of air which is ascending or descending without exchanging heat with its environment.
) is the temperature gradient experienced in an ascending or descending packet of air that is not saturated with water vapor, i.e., with less than 100% relative humidity.
After saturation, the rising air follows the moist (or wet) adiabatic lapse rate.
[20] The release of latent heat is an important source of energy in the development of thunderstorms.
) is the temperature gradient experienced in an ascending or descending packet of air that is saturated with water vapor, i.e., with 100% relative humidity.
The varying environmental lapse rates throughout the Earth's atmosphere are of critical importance in meteorology, particularly within the troposphere.
As unsaturated air rises, its temperature drops at the dry adiabatic rate.
The dew point also drops (as a result of decreasing air pressure) but much more slowly, typically about 2 °C per 1,000 m. If unsaturated air rises far enough, eventually its temperature will reach its dew point, and condensation will begin to form.
If the environmental lapse rate is between the moist and dry adiabatic lapse rates, the air is conditionally unstable — an unsaturated parcel of air does not have sufficient buoyancy to rise to the LCL or CCL, and it is stable to weak vertical displacements in either direction.
The temperature decreases with the dry adiabatic lapse rate, until it hits the dew point, where water vapor in the air begins to condense.
[24] If the environmental lapse rate was zero, so that the atmosphere was the same temperature at all elevations, then there would be no greenhouse effect.
[25] The presence of greenhouse gases on a planet causes radiative cooling of the air, which leads to the formation of a non-zero lapse rate.
In Antarctica, thermal inversions in the atmosphere (so that air at higher altitudes is warmer) sometimes cause the localized greenhouse effect to become negative (signifying enhanced radiative cooling to space instead of inhibited radiative cooling as is the case for a positive greenhouse effect).
[26][27] A question has sometimes arisen as to whether a temperature gradient will arise in a column of still air in a gravitational field without external energy flows.
Maxwell also concluded that the universal result must be one in which the temperature is uniform, i.e., the lapse rate is zero.
[28] Santiago and Visser (2019) confirm the correctness of Maxwell's conclusion (zero lapse rate) provided relativistic effects are neglected.
Santiago and Visser remark that "gravity is the only force capable of creating temperature gradients in thermal equilibrium states without violating the laws of thermodynamics" and "the existence of Tolman's temperature gradient is not at all controversial (at least not within the general relativity community).
