# International Standard Atmosphere

File:Comparison International Standard Atmosphere space diving.svg
Comparison of a graph of International Standard Atmosphere temperature and pressure and approximate altitudes of various objects and successful stratospheric jumps

The International Standard Atmosphere (ISA) is an atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations. It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes, plus some formulas by which those values were derived. The International Organization for Standardization (ISO) publishes the ISA as an international standard, ISO 2533:1975.[1] Other standards organizations, such as the International Civil Aviation Organization (ICAO) and the United States Government, publish extensions or subsets of the same atmospheric model under their own standards-making authority.

## Description

The ISA model divides the atmosphere into layers with linear temperature distributions.[2] The other values are computed from basic physical constants and relationships. Thus the standard consists of a table of values at various altitudes, plus some formulas by which those values were derived. For example, at sea level the standard gives a pressure of 1013.25 hPa (1 atm) and a temperature of 15 degrees Celsius, and an initial lapse rate of −6.5 °C/km (roughly −2 °C/1,000 ft). The tabulation continues to 11 km where the pressure has fallen to 226.32 hPa and the temperature to −56.5 °C. Between 11 km and 20 km the temperature remains constant.[3][4]

Layers in the ISA Standard Atmosphere 1976
Layer Level
Name
Base
Geopotential
Altitude above MSL[5]
h (in km)
Base
Geometric
Altitude above MSL[5]
z (in km)

Lapse
Rate
(in °C/km)[a]

Base
Temperature
T (in °C)
Base
Atmospheric
Pressure
p (in Pa)
0 Troposphere 0.0 0.0 −6.5 +15.0 101325
1 Tropopause 11.000 11.019 +0.0 −56.5 22632
2 Stratosphere 20.000 20.063 +1.0 −56.5 5474.9
3 Stratosphere 32.000 32.162 +2.8 −44.5 868.02
4 Stratopause 47.000 47.350 +0.0 −2.5 110.91
5 Mesosphere 51.000 51.413 −2.8 −2.5 66.939
6 Mesosphere 71.000 71.802 −2.0 −58.5 3.9564
7 Mesopause 84.852 86.000 −86.28 0.3734
a lapse rate given per kilometer of geopotential altitude

In the above table, geopotential altitude is calculated from a mathematical model that adjusts the altitude to include the variation of gravity with height, while geometric altitude is the standard direct vertical distance above mean sea level.[2] Note that the Lapse Rates cited in the table are given as °C per kilometer of geopotential altitude, not geometric altitude.

The ISA model is based on average conditions at mid latitudes, as determined by the ISO's TC 20/SC 6 technical committee. It has been revised from time to time since the middle of the 20th century.

## ICAO Standard Atmosphere

The International Civil Aviation Organization (ICAO) published their "ICAO Standard Atmosphere" as Doc 7488-CD in 1993. It has the same model as the ISA, but extends the altitude coverage to 80 kilometres (262,500 feet).[6]

The ICAO Standard Atmosphere does not contain water vapour.

Some of the values defined by ICAO are:

ICAO Standard Atmosphere
Height km & ft Temperature °C Pressure hPa Lapse Rate °C/1000 ft
0 km MSL 15.0 1013.25 −1.98 (Tropospheric)
11 km 36 000 ft −56.5 226.00 0.00 (Stratospheric)
20 km 65 000 ft −56.5 54.70 +0.3 (Stratospheric)
32 km 105 000 ft −44.5 8.68

Aviation standards and flying rules are based on the International Standard Atmosphere. Airspeed indicators are calibrated on the assumption that they are operating at sea level in the International Standard Atmosphere where the air density is 1.225 kg/m3. The standard is very useful in meteorology for comparison against actual values.

## Other standard atmospheres

The U.S. Standard Atmosphere is a set of models that define values for atmospheric temperature, density, pressure and other properties over a wide range of altitudes. The first model, based on an existing international standard, was published in 1958 by the U.S. Committee on Extension to the Standard Atmosphere,[7] and was updated in 1962,[5] 1966,[8] and 1976.[9] The U.S. Standard Atmosphere, International Standard Atmosphere and WMO (World Meteorological Organization) standard atmospheres are the same as the ISO International Standard Atmosphere for altitudes up to 32 km.[10][11]

NRLMSISE-00 is an empirical, global model of the Earth's atmosphere from ground to space. It models the temperatures and densities of the atmosphere's components. A primary use of this model is to aid predictions of satellite orbital decay due to atmospheric drag.

The standard conditions for temperature and pressure are a model of gas temperature and pressure used in chemistry.

## References

1. ^ International Organization for Standardization, Standard Atmosphere, ISO 2533:1975, 1975.
2. ^ a b Gyatt, Graham (2006-01-14): "The Standard Atmosphere". A mathematical model of the 1976 U.S. Standard Atmosphere.
3. ^ Auld, D.J.; Srinivas, K. (2008). "Properties of the Atmosphere". Retrieved 2008-03-13.
4. ^ Batchelor, G. K., An Introduction to Fluid Dynamics, Cambridge Univ. Press, 1967.
5. ^ a b c U.S. Standard Atmosphere, 1962, U.S. Government Printing Office, Washington, D.C., 1962
6. ^ International Civil Aviation Organization, Manual of the ICAO Standard Atmosphere (extended to 80 kilometres (262 500 feet)), Doc 7488-CD, Third Edition, 1993, ISBN 92-9194-004-6.
7. ^ U.S. Extension to the ICAO Standard Atmosphere, U.S. Government Printing Office, Washington, D.C., 1958
8. ^ U.S. Standard Atmosphere Supplements, 1966, U.S. Government Printing Office, Washington, D.C., 1966
9. ^ U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976 (Linked file is 17 MB)
10. ^
11. ^ Tomasi, C.; Vitake, V.; De Santis, L.V. (1998). "Relative optical mass functions for air, water vapour, ozone and nitrogen dioxide in atmospheric models presenting different latitudinal and seasonal conditions" (PDF). Meteorology and Atmospheric Physics 65 (1): 11–30. Bibcode:1998MAP....65...11T. doi:10.1007/BF01030266. Retrieved 2007-12-31. …the ISO (International Organisation for Standardisation) Standard Atmosphere, 1972. This model is identical to the present Standard Atmospheres of ICAO (International Civil Aviation Organization) and WMO (World Meteorological Organization) up to a height of 32 km
• Davies, Mark (2003). The Standard Handbook for Aeronautical and Astronautical Engineers. New York: McGraw-Hill. ISBN 0-07-136229-0.