International Standard Atmosphere
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.
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 and a temperature of 15 °C, and an initial lapse rate of −6.5 °C/km. The tabulation continues to 11 km where the pressure has fallen to 22.632 kPa and the temperature to −56.5 °C. Between 11 km and 20 km the temperature remains constant. [3][4]
| 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 |
In the above table, geopotential height is calculated from a mathematical model in which the acceleration due to gravity is assumed constant. Geometric height results from the (more accurate) assumption that gravity obeys an inverse square law.[citation needed]
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.
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).[5]
The ICAO Standard Atmosphere does not contain water vapour
Some of the values defined by ICAO are:
| Height km & ft | Temperature °C | Pressure hPa | Lapse Rate °C/1000ft |
|---|---|---|---|
| 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 | −1.00 (Stratospheric) |
| 32 km 105,000 ft | −44.5 | 8.68 |
As this is a Standard, you will never encounter these conditions outside of a laboratory, but many Aviation standards and flying rules are based on this, altimetry being a major one. The standard is very useful in Meteorology for comparing actual values against.
Other standard atmospheres
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, ICAO 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
- ^ International Organization for Standardization, Standard Atmosphere, ISO 2533:1975, 1975.
- ^ Gyatt, Graham (2006-01-14): "The Standard Atmosphere". A mathematical model of the 1976 U.S. Standard Atmosphere.
- ^ Auld, D.J.; Srinivas, K. (2008), Properties of the Atmosphere, retrieved 2008-03-13
- ^ Batchelor, G. K., An Introduction to Fluid Dynamics, Cambridge Univ. Press, 1967.
- ^ 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.
- ^ U.S. Extension to the ICAO Standard Atmosphere, U.S. Government Printing Office, Washington, D.C., 1958
- ^ U.S. Standard Atmosphere, 1962, U.S. Government Printing Office, Washington, D.C., 1962
- ^ U.S. Standard Atmosphere Supplements, 1966, U.S. Government Printing Office, Washington, D.C., 1966
- ^ U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976 (Linked file is 17 MB)
- ^ NASA, "U.S. Standard Atmosphere 1976"
- ^ Tomasi, C. (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. 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
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- Davies, Mark (2003). The Standard Handbook for Aeronautical and Astronautical Engineers. New York: McGraw-Hill. ISBN 0071362290.
- ICAO Standard Atmosphere Table
- NASA JPL Reference Notes
- ICAO, Manual of the ICAO Standard Atmosphere (extended to 80 kilometres (262 500 feet)), Doc 7488-CD, Third Edition, 1993, ISBN 92-9194-004-6.