The
International Standard Atmosphere (ISA) is an
atmospheric modelStatic atmospheric models describe how the ideal gas properties of an atmosphere change, primarily as a function of altitude....
of how the
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
,
temperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
,
densityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, and
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of the
Earth's atmosphereThe atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
change over a wide range of
altitudeAltitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
s. It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes, plus some
formulaIn mathematics, a formula is an entity constructed using the symbols and formation rules of a given logical language....
e by which those values were derived. The
International Organization for StandardizationThe International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
(ISO), publishes the ISA as an
international standardInternational standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
, ISO 2533:1975. Other
standards organizationA standards organization, standards body, standards developing organization , or standards setting organization is any organization whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise producing technical standards that are...
s, such as the
International Civil Aviation OrganizationThe International Civil Aviation Organization , pronounced , , is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth...
(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. 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
formulaIn mathematics, a formula is an entity constructed using the symbols and formation rules of a given logical language....
s by which those values were derived. For example, at sea level the standard gives a pressure of 1013.25
hPa-Organizations:*Halifax Port Authority, a port authority in Canada*Hamburg Port Authority, the port authority for the Port of Hamburg, Germany*Health Protection Agency, a health organization in the United Kingdom...
(1
atmThe standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...
) and a temperature of 15 Celsius, and an initial
lapse rateThe lapse rate is defined as the rate of decrease with height for an atmospheric variable. The variable involved is temperature unless specified otherwise. The terminology arises from the word lapse in the sense of a decrease or decline; thus, the lapse rate is the rate of decrease with height and...
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.
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 The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
|
0.0 |
0.0 |
−6.5 |
+15.0 |
101325 |
| 1 |
TropopauseThe tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
|
11.000 |
11.019 |
+0.0 |
−56.5 |
22632 |
| 2 |
StratosphereThe stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
|
20.000 |
20.063 |
+1.0 |
−56.5 |
5474.9 |
| 3 |
StratosphereThe stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
|
32.000 |
32.162 |
+2.8 |
−44.5 |
868.02 |
| 4 |
Stratopause The stratopause is the level of the atmosphere which is the boundary between two layers, stratosphere and the mesosphere...
|
47.000 |
47.350 |
+0.0 |
−2.5 |
110.91 |
| 5 |
Mesosphere The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...
|
51.000 |
51.413 |
−2.8 |
−2.5 |
66.939 |
| 6 |
Mesosphere The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...
|
71.000 |
71.802 |
−2.0 |
−58.5 |
3.9564 |
| 7 |
Mesopause The mesopause is the temperature minimum at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesopause is the coldest place on Earth with temperatures as low as -100°C...
|
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.
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 OrganizationThe International Civil Aviation Organization , pronounced , , is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth...
(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).
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 |
|
As this is a Standard, you will not always 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 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, and was updated in 1962, 1966, and 1976. 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.
NRLMSISE-00NRLMSISE-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...
is an
empiricalThe word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....
, global
modelA mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
of the
Earth's atmosphereThe atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
from ground to space. It models the
temperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
s and
densitiesThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the atmosphere's components. A primary use of this model is to aid predictions of
satelliteIn the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
orbital decay due to atmospheric drag.
The
standard conditions for temperature and pressureStandard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...
are a model of gas temperature and pressure used in
chemistryChemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
.
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