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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 ]
(A reading of 922.5 mbar (corrected to MSL) was reported from Omagh in Co. Tyrone (Harding 1887) the graduation and calibration of the barometer were not considered satisfactory enough “to quote the reading as trustworthy”, the storm minimum over the Northern Ireland was thought to be close to 924 mbar.)
It is used for barometric pressure in weather reports, refrigeration and aviation in the United States. It is the pressure exerted by a column of mercury 1 inch (25.4 mm) in height at the standard acceleration of gravity. Conversion to metric units depends on the density of mercury, and hence its temperature; typical conversion factors are: [1]
For example, if a barometer located at sea level and under fair weather conditions is moved to an altitude of 1,000 feet (305 m), about 1 inch of mercury (~35 hPa) must be added on to the reading. The barometer readings at the two locations should be the same if there are negligible changes in time, horizontal distance, and temperature.
However, with a barometric pressure of 895 mbar (hPa; 26.43 inHg), Rita is the strongest tropical cyclone ever recorded in the Gulf of Mexico. [64] In between Rita and Katrina is Hurricane Allen. Allen's pressure was measured at 899 mbar. Hurricane Camille is the sixth strongest hurricane on record.
When the barometric pressure falls at least 0.71 of an inch of mercury (24 millibars) in 24 hours, a storm has undergone bombogenesis. For example, a weak storm that began with a barometric ...
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 ...
This storm system had, in part, a large effect on the weather in the entire eastern half of the country. A number of different weather records (at the time) were set during the four days of this storm, especially in daily high temperatures, wind gusts, low barometric pressure readings, and number of tornadoes. [1]