Editing Lapse rate (section)

== Environmental lapse rate ==
A formal definition from the ''Glossary of Meteorology''<ref name="Glossary of Meteorology">{{cite book|author=Todd S. Glickman|title=Glossary of Meteorology|edition=2nd|publisher=[[American Meteorological Society]], [[Boston]]|date=June 2000|isbn=978-1-878220-34-9}} [http://www.ametsoc.org/pubs/glossary_index.html (Glossary of Meteorology)]</ref> is:
:The decrease of an atmospheric variable with height, the variable being temperature unless otherwise specified.

Typically, the lapse rate is the negative of the rate of temperature change with altitude change:

:<math>\Gamma = -\frac{\mathrm{d}T}{\mathrm{d}z}</math>

where <math>\Gamma</math> (sometimes <math>L</math>) is the lapse rate given in [[physical unit|unit]]s of temperature divided by units of altitude, ''T'' is temperature, and ''z'' is altitude.{{efn|Note: <math>\Gamma</math> and <math>\gamma</math> are both used in this article but with very distinct meanings.<ref>{{cite book | author=Salomons, Erik M. | title=Computational Atmospheric Acoustics | edition=1st | publisher=Kluwer Academic Publishers| year=2001 | isbn=978-1-4020-0390-5}}</ref><ref>{{cite book | author=Stull, Roland B. | title=An Introduction to Boundary Layer Meteorology | edition=1st | publisher=Kluwer Academic Publishers| year=2001 | isbn=978-90-277-2769-5}}</ref>}}

The ''environmental lapse rate'' (ELR), is the actual rate of decrease of temperature with altitude in the atmosphere at a given time and location.<ref name="Daidzic19">{{cite journal |last1=Daidzic |first1=Nihad E. |title=On Atmospheric Lapse Rates |journal=International Journal of Aviation, Aeronautics, and Aerospace |date=2019 |volume=6 |issue=4 |doi=10.15394/ijaaa.2019.1374 |url=https://commons.erau.edu/cgi/viewcontent.cgi?article=1374&context=ijaaa|doi-access=free }}</ref>

As an average, the [[International Civil Aviation Organization]] (ICAO) defines an [[international standard atmosphere]] (ISA) with a temperature lapse rate of {{nowrap|6.50&nbsp;°C/km}}<ref name="ICAO 1993">{{cite book|publisher=[[International Civil Aviation Organization]]|title=Manual of the ICAO Standard Atmosphere (extended to 80 kilometres (262 500 feet))|id=Doc 7488-CD|edition=Third|year=1993|isbn=978-92-9194-004-2}}</ref> {{nowrap|(3.56&nbsp;°F}} or {{nowrap|1.98&nbsp;°C/1,000 ft)}} from sea level to 11&nbsp;km {{nowrap|(36,090 ft}} or {{nowrap|6.8&nbsp;mi)}}. From 11&nbsp;km up to 20&nbsp;km {{nowrap|(65,620 ft}} or {{nowrap|12.4&nbsp;mi)}}, the constant temperature is {{nowrap|−56.5&nbsp;°C}} {{nowrap|(−69.7&nbsp;°F)}}, which is the lowest assumed temperature in the ISA. The [[ICAO Standard Atmosphere|standard atmosphere]] contains no moisture. 

Unlike the idealized ISA, the temperature of the actual atmosphere does not always fall at a uniform rate with height. For example, there can be an [[Temperature inversion|inversion]] layer in which the temperature increases with altitude.