Standard atmosphere

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The standard atmosphere , normal atmosphere or standard atmosphere is a term from aviation and describes idealized properties of the earth's atmosphere .

The International Standard Atmosphere (Engl. International Standard Atmosphere , ISA) is from the International Civil Aviation Organization has been defined (ICAO). It represents an atmosphere in which the parameters air pressure, air temperature, air humidity and temperature decrease per 100 m altitude have values ​​that are roughly equal to the mean values ​​prevailing on earth. The international standard atmosphere thus roughly corresponds to the pressure and temperature conditions (15 ° C and 1013.25  hPa ) prevailing  in mid-latitudes of 40 ° north .

The aim is to create an internationally uniform reference value and not to provide an exact description of the current, local atmosphere. The international standard atmosphere corresponds to the US standard atmosphere in 1976 up to an altitude of 32 km . Previously, a standard known as the International Standard Atmosphere was used. In Germany there was also the DIN 5450 standard atmosphere , in 1975 the standard atmosphere was specified in DIN ISO 2533.



Standard atmosphere

The defined properties are z. B. needed to correct the performance values ​​of an engine run in a test stand and to be able to make a statement about whether this engine produces enough thrust to be able to accelerate an aircraft sufficiently on the runway .

The use of a standard atmosphere is necessary to calculate the performance data of aircraft, engines and rockets. It is also used to calibrate pressure measuring devices such as B. Altimeter and Speedometer.

The following conditions apply to these at medium sea level:

parameter metric system of measurement imperial system of measurement
Humidity / H 2 O 0 rel. % 0
Pressure p 0 1013.25 hPa 29.92 inHg
Density ρ 0 1.225 kg / m 3 0.002378 slug / ft 3
Temperature T 0 15 ° C / 288.15 K 59 ° F / 518.67 ° R
Speed ​​of sound a 0 340 m / s 1116.4 ft / s
Gravity 9.80665 m / s 2 32.174 ft / s 2

The classification of the atmosphere is also described. The following applies here:

  • The temperature gradient from sea level to the tropopause is −6.5 K / 1,000 m (−3,564 ° F / 1,000 ft).
  • The tropopause is at an altitude of 11,000 m (36,089 ft).
  • In the stratosphere there is a constant temperature of −56.5 ° C (216.65 K; -69.7 ° F)

The temperature at an altitude below the tropopause can be calculated using the following formula:

Metric system:

Imperial system:

The unit of height (meter or foot) is shortened with the unit of length of the temperature gradient or results in an additional conversion factor.

Terrestrial refraction

Similar models

US standard atmosphere 1976

The ICAO (International Civil Aviation Organization) defined a generally applicable and binding standard atmosphere for aviation in 1976 with ICAO document 7488. This replaces a previous version from 1962. The following are defined as uniform conditions at sea level that correspond to an average level of moderate latitudes:

The temperature profile with the height is defined according to the following table, with linear interpolation between the explicitly defined levels. The top level is also the upper limit of this model.

Standard atmosphere 1976 up to 90 km altitude

In addition, u. a. the following values ​​are defined as constants:

Standard atmosphere 1976
geopot. Height h
in m
geometr. Height z
in m
Temperature T
in ° C
Air pressure p
in Pa
00.000 00.000 -15th, 0 101,325, 0000
11,000 11,019 −56.5 022,632, 0000
20,000 20,063 −56.5 005,474.9000
32,000 32,162 −44.5 000.868.0200
47,000 47,350 0−2.5 000.110.91000.
51,000 51,413 0−2.5 000.066.9390
71,000 71,802 −58.5 000.003.9564
84,852 86,000 −86.2 000.000.3734

The air density at sea level is calculated from this at 1.225 kg / m³.

It is assumed that the air fulfills certain principles in an ideal way, in particular the general gas equation . This allows the altitude-dependent air pressure to be calculated. This gives the international barometric altitude formula for the bottom layer . The barometric height formula with a linear temperature profile results for layers with a linear temperature profile .

The standard atmosphere works with standard pressure areas of the geopotential heights , since the acceleration due to gravity is assumed to be independent of altitude. At low altitudes these correspond pretty well with the usual geometric heights, but for greater accuracy at higher altitudes, instead of the geometric height z, an imaginary homogeneous gravitational field with the corresponding geopotential height h must be used. The relationship between the two is by the equation


Jacchia reference atmosphere

The Jacchia reference atmosphere, which is particularly used in space travel , describes an atmosphere model that is defined for altitudes from 90 to 2,500 km for atmospheric values ​​such as temperature, density, pressure and other values. In contrast to the international standard atmosphere, different values ​​depending on latitude and season as well as geomagnetic and solar effects are also taken into account. In addition, another atmosphere model must be used for lower altitudes.

The Jacchia reference atmosphere model was first published in 1970 by Luigi Giuseppe Jacchia and updated in 1971 and 1977. It is based on air resistance measurement data from space flights and is mainly used for space travel.

NRLMSISE-00 model

The newer NRLMSISE-00 model from 2000 provides reference values for heights from the surface of the earth to space.

See also

Individual evidence

  1. ( Page no longer available , search in web archives: ICAO original document 7488, 3rd edition from 1993 (up to 80 km altitude) )@1@ 2Template: Dead Link /
  2. ICAO standard atmosphere 1976  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 89 kB) Archived copy ( memento of the original from September 16, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 480 kB)@1@ 2Template: Toter Link /   @1@ 2Template: Webachiv / IABot /

Web links

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