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Atmospheric pressure
The air in its state of
rest exerts a pressure directed perpendicular to each, any oriented surface.
The static pressure acting on the surface of the earth is called atmospheric
pressure. It is caused by the weight of a column of air reaching from the earth
surface up to the top of the atmosphere. Atmospheric pressure is measured in
hectopascals (hPa) or as the length of a column of mercury (mmHg) at
To measure atmospheric pressure, aneroid barometers use the deformation of a
flat circular metal box exhausted of air with faces corrugated for strength
(aneroid capsule). Variations of the external atmospheric pressure cause changes
in the displacement of the walls of the box as long as a new equilibrium position
is reached so that there is equilibrium between the elastic walls and the atmospheric
pressure.
absolute air pressure and air pressure corrected to see level
With increasing altitude the column of air reaching from the earth surface up
to the top of the atmosphere gets shorter and therefore the absolute atmospheric
pressure drops. Near the earth surface a difference in altitude of about
The conversion from the absolute atmospheric pressure to the atmospheric
pressure at see level is done by adding a value of pressure in accordance to
the altitude difference.
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p
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abs
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= absolute atmospheric pressure [hPa] |
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p
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red
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= atmospheric pressure with altitude reduced to see level [hPa] |
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p
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= pressure difference [hPa] |
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h
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= altitude [m above see level] | |
| h [m NN] |
p [hPa] |
h [m NN] |
p [hPa] |
|
| 100 200 300 400 500 600 700 800 900 1000 |
12,0 23,8 35,5 47,2 58,7 70,1 81,3 92,5 103,6 114,5 |
1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 |
125,4 136,1 146,8 157,3 167,7 178,1 188,3 198,4 208,4 218,4 |
