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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 low-pressure area is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence that occur in the upper levels of the troposphere. [1] The formation process of a low-pressure area is known as cyclogenesis. [2]
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible rain or storms), [1] while high-pressure areas are associated with lighter winds and clear skies. [2]
Atmospheric pressure in low Earth orbit, around 500 km altitude [13] [14] 10 −7 Pa. 100 nPa ... Extremely high-pressure chemical reactors (10 kbar) [citation needed]
Isobars, lines of equal pressure, when drawn on such a map, give a contour map showing areas of high and low pressure. [33] Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Atmospheric lift caused by low-level wind convergence into the surface brings clouds and sometimes precipitation ...
A trough is an elongated region of relatively low atmospheric pressure without a closed isobaric contour that would define it as a low pressure area. Since low pressure implies a low height on a pressure surface, troughs and ridges refer to features in an identical sense as those on a topographic map. Troughs may be at the surface, or aloft, at ...
Other units of pressure include: The bar (symbol: bar), defined as 100 kPa exactly. The atmosphere (symbol: atm), defined as 101.325 kPa exactly. These four pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures. [7] The torr is used in high-vacuum physics and engineering. [8] [9]
Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10 −12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm 3. [4] Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space.