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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 atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is ...
The bar is a metric unit of pressure defined as 100,000 Pa (100 kPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea level (approximately 1.013 bar).
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.
QNE is an aeronautical code Q code.The term refers to the indicated altitude at the landing runway threshold when or is set in the altimeter's Kollsman window. It is the pressure altitude at the landing runway threshold.
p (Pa) Base atmospheric density ρ (kg/m 3) 0 Troposphere: 0 0 -6.5 +15.0 (288.15) 101,325 1.225 1 Tropopause: 11,000 11,019 0.0 −56.5 (216.65) 22632 0.3639 2 Stratosphere: 20,000 20,063 +1.0 −56.5 (216.65) 5474.9 0.0880 3 Stratosphere: 32,000 32,162 +2.8 −44.5 (228.65) 868.02 0.0132 4 Stratopause: 47,000 47,350 0.0 −2.5 (270.65) 110.91 ...
Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 10 5 Pa (100 kPa, 1 bar). NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). [3] This standard is also called normal temperature and pressure (abbreviated as NTP).
Aircraft altimeters measure the relative pressure difference between the lower ambient pressure at altitude and a calibrated reading on the ground. In the United States, Canada [2] and Japan, these altimeter readings are provided in inches of mercury, but most other nations use hectopascals.
Altimeter setting is the value of the atmospheric pressure used to adjust the scale of a pressure altimeter so that it indicates the height of an aircraft above a known reference surface. [1]