International Standard Atmosphere
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The International Standard Atmosphere (ISA) is a model of the standard variation of pressure, temperature, density, and viscosity with altitude in the Earth's atmosphere. It is based on average conditions at mid latitudes, as determined by the International Civil Aviation Organization (ICAO). The atmosphere is divided into layers with assumed temperature distributions, and the other values are computed from basic physical constants and relationships.
Various tabulations of the 1976 standard may be found on the web, e.g. at [1], or, of an earlier but similar standard, in publications such as Appendix 1 of Batchelor. The latter tabulation gives at sea level 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.
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[edit] Layers in the ISA
| 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 |
[edit] See also
[edit] References
- Batchelor, G. K., An Introduction to Fluid Dynamics, Cambridge Univ. Press, 1967.
- Tabulation of 1976 standard at University of Sydney aeronautical mechanics site
- 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.
[edit] External link
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