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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. It 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.

Contents

Description

Development of the ISA

Other standard atmospheres

References

See also

External links

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 1.013 bar and a temperature of 15°C, and an initial lapse rate of -6.5 °C/km. Above 12km the tabulated temperature is essentially constant. The tabulation continues to 18km where the pressure has fallen to 0.075 bar and the temperature to -56.5 °C.^[3][4]

Layers in the ISA

Standard Atmosphere 1976

Layer	Level Name	Base Geopotential Height ''h'' (in km)	Base Geometric Height ''z'' (in km)	Lapse Rate (in °C/km)	Base Temperature ''T'' (in °C)	Base Atmospheric Pressure ''p'' (in Pa)
0	Troposphere	0.0	0.0	-6.5	+15.0	101,325
1	Tropopause	11.000	11.019	+0.0	-56.5	22,632
2	Stratosphere	20.000	20.063	+1.0	-56.5	5,474.9
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	—	-86.2	0.3734

Development of the ISA

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

Other standard atmospheres

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).^[5]
The U.S. Standard Atmosphere is 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,^[6] and was updated in 1962,^[7] 1966,^[8] and 1976.^[9] The U.S. Standard Atmosphere is the same as the ICAO Standard Atmosphere for altitudes up to 32km.^[10]
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

★ The Standard Handbook for Aeronautical and Astronautical Engineers, , Mark, Davies, McGraw-Hill, 2003,
1. International Organization for Standardization, ''Standard Atmosphere'', ISO 2533:1975, 1975.
2. Gyatt, Graham (2006-01-14): "The Standard Atmosphere". A mathematical model of the 1976 U.S. Standard Atmosphere.
3.
http://www.aeromech.usyd.edu.au/aero/atmos/atmtab.html, Tabulation of 1976 standard at University of Sydney aeronautical mechanics site
4. Batchelor, G. K., ''An Introduction to Fluid Dynamics'', Cambridge Univ. Press, 1967.
5. 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.
6. U.S. Extension to the ICAO Standard Atmosphere, U.S. Government Printing Office, Washington, D.C., 1958
7. U.S. Standard Atmosphere, 1962, U.S. Government Printing Office, Washington, D.C., 1962
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. NASA, "U.S. Standard Atmosphere 1976"

See also

★ Density of air

External links