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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 ]
at each geopotential altitude, where g is the standard acceleration of gravity, and R specific is the specific gas constant for dry air (287.0528J⋅kg −1 ⋅K −1). The solution is given by the barometric formula. Air density must be calculated in order to solve for the pressure, and is used in calculating dynamic pressure for moving vehicles.
Highest air pressure: 20 January 2020, Abbeville, Somme 1049.7 hPa [185] [186] Previously: 3 March 1990, Pointe de Chémoulin, Saint-Nazaire Loire-Atlantique 1048.9 hPa. [187] Lowest air pressure: 25 February 1989, Cap de La Hague, Cherbourg 951.8 hPa. [187] though other listed figures predate Météo-France's records. [citation needed]
Comparison of the 1962 US Standard Atmosphere graph of geometric altitude against air density, pressure, the speed of sound and temperature with approximate altitudes of various objects. [ 1 ] The U.S. Standard Atmosphere is a static atmospheric model of how the pressure , temperature , density , and viscosity of the Earth's atmosphere change ...
The general synopsis follows, giving the position, pressure (in millibars) and track of pressure areas (e.g., "Low, Rockall, 987, deepening rapidly, expected Fair Isle 964 by 0700 tomorrow"). With the information provided in the Shipping Forecast it is possible to compile a pressure chart for the coasts of northwestern Europe.
Commonly, the drum makes one revolution per day, per week, or per month and the rotation rate can often be selected by the user. Various other types of barograph have also been invented. Karl Kreil described a machine in 1843 based on a syphon barometer, where a pencil marked a chart at uniform intervals. [3]
On the top right corner of the model for a surface weather map is the pressure, showing the last two integer digits of the pressure in millibars, or hectopascals, along with the first decimal. For instance, if the pressure at a certain location is 999.7 hPa, the pressure portion of the station model will read 997.
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.