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Atmospheric air pressure where standard atmospheric pressure is defined as 1013.25 mbar, 101.325 kPa, 1.01325 bar, which is about 14.7 pounds per square inch. Despite the millibar not being an SI unit, meteorologists and weather reporters worldwide have long measured air pressure in millibar as the values are convenient.
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa ), which is equivalent to 1,013.25 millibars , [ 1 ] 760 mm Hg , 29.9212 inches Hg , or 14.696 psi . [ 2 ]
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
Pressure as a function of the height above the sea level. There are two equations for computing pressure as a function of height. The first equation is applicable to the atmospheric layers in which the temperature is assumed to vary with altitude at a non null lapse rate of : = [,, ()] ′, The second equation is applicable to the atmospheric layers in which the temperature is assumed not to ...
For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). [2] The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m). [10]
Comparison of a graph of International Standard Atmosphere temperature and pressure and approximate altitudes of various objects and successful stratospheric jumps The International Standard Atmosphere ( ISA ) is a static atmospheric model of how the pressure , temperature , density , and viscosity of the Earth's atmosphere change over a wide ...
Standard pressure, the baseline used universally, is 1013.25 hectopascals (hPa), which is equivalent to 1013.25 mb or 29.92 inches of mercury (inHg). This setting is equivalent to the atmospheric pressure at mean sea level (MSL) in the ISA.
SPS/STD - 'Standard Pressure Setting' or just 'Standard' refers to the altimeter being set to the standard pressure of 1013.25 hPa. It is the setting that causes an altimeter to read the aircraft's flight level (FL). Flight levels are given in hundreds of feet (for example: FL100 = 10 000 ft). Atmospheric pressure changes over time and position.