Atmospheric pressure is the pressure at any given point in the Earth's atmosphere. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Fluid pressure is the Pressure at some point within a Fluid, such as water or air In the Physical sciences weight is a Measurement of the gravitational Force acting on an object Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation. A column of air 1 square inch in cross section, measured from sea level to the top of the atmosphere, would weigh approximately 14. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface 7 lbf. This article deals with the unit of force For the unit of mass see Pound (mass. A 1 m² (11 sq ft) column of air would weigh about 100 kilonewtons (equivalent to a mass of 10. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical 2 tonnes at the surface). This article is about the tonne or metric ton For other tons see Ton.

Standard atmospheric pressure

The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being precisely equal to 101. The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface 325 kPa. The following non-standard units are equivalent: 760 mmHg (torr), 29. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. 92 inHg or 14. Inches of mercury, inHg or "Hg is a measuring unit for Pressure. 696 PSI. The pound per square inch or more accurately pound-force per square inch (symbol psi or lbf/in² or lbf/in²) is a unit of One standard atmosphere is standard pressure used for pneumatic fluid power (ISO R554), and in the aerospace (ISO 2533) and petroleum (ISO 5024) industries.

In 1999, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, “the standard pressure” should be defined as precisely 100 kPa (≈750. The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization 01 torr) or 29. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. 53 inHg rather than the 101. Inches of mercury, inHg or "Hg is a measuring unit for Pressure. 325 kPa value of “one standard atmosphere”. ^[1] This value is used as the standard pressure for the compressor and the pneumatic tool industries (ISO 2787). ^[2] (See also Standard temperature and pressure. In Physical sciences standard conditions for temperature and pressure are Standard sets of conditions for experimental measurements to allow comparisons to be made ) In the United States, compressed air flow is often measured in "standard cubic feet" per unit of time, where the "standard" means the equivalent quantity of moisture at standard temperature and pressure. The United States of America —commonly referred to as the However, this standard atmosphere is defined slightly differently: temperature = 20 °C (68 °F), air density = 1. 225 kg/m³ (0. 0765 lb/cu ft), altitude = sea level, and relative humidity = 20%. In the air conditioning industry, the standard is often temperature = 0 °C (32 °F) instead. For natural gas, the petroleum industry uses a standard temperature of 15. 6 °C (60. 08 °F), pressure 101. 56 kPa (14. 73 psi).

Mean sea level pressure

15 year average MSLP for JJA (top) and DJF (bottom)
JJA: June July August
DJF: December January February

Mean sea level pressure (MSLP or QFF) is the pressure at sea level or (when measured at a given elevation on land) the station pressure reduced to sea level assuming an isothermal layer at the station temperature.

This is the pressure normally given in weather reports on radio, television, and newspapers or on the Internet. When barometers in the home are set to match the local weather reports, they measure pressure reduced to sea level, not the actual local atmospheric pressure. See Altimeter (barometer vs. absolute). An altimeter is an instrument used to measure the Altitude of an object above a fixed level

The reduction to sea level means that the normal range of fluctuations in pressure is the same for everyone. The pressures which are considered high pressure or low pressure do not depend on geographical location. This makes isobars on a weather map meaningful and useful tools.

The altimeter setting in aviation, set either QNH or QFE, is another atmospheric pressure reduced to sea level, but the method of making this reduction differs slightly. QNH is a Q code. It is a pressure setting used by pilots, Air traffic control (ATC and Low frequency Weather beacons to refer to See altimeter. An altimeter is an instrument used to measure the Altitude of an object above a fixed level

• QNH: The barometric altimeter setting which will cause the altimeter to read airfield elevation when on the airfield. In ISA temperature conditions the altimeter will read altitude above mean sea level in the vicinity of the airfield
• QFE: The barometric altimeter setting which will cause an altimeter to read zero when at the reference datum of a particular airfield (generally a runway threshold). In ISA temperature conditions the altimeter will read height above the datum in the vicinity of the airfield.

QFE and QNH are arbitrary Q codes rather than abbreviations, but the mnemonics "Nautical Height" (for QNH) and "Field Elevation" (for QFE) are often used by pilots to distinguish them. A mnemonic device (nəˈmɒnɪk is a Memory aid Commonly met mnemonics are often verbal something such as a very short poem or a special word used to help a person remember

Average sea-level pressure is 101. 325 kPa (1013. 25 mbar) or 29. 921 inches of mercury (inHg) or 760 millimeters (mmHg). In aviation weather reports (METAR), QNH is transmitted around the world in millibars or hectopascals (1 millibar = 1 hectopascal), except in the United States and in Canada where it is reported in inches (or hundredths of inches) of mercury. METAR (METeorological Aviation Report is a format for reporting Weather information (The United States and Canada also report sea level pressure SLP, which is reduced to sea level by a different method, in the remarks section, not an internationally transmitted part of the code, in hectopascals or millibars ^[3]. However, in Canada's public weather reports, sea level pressure is instead reported in kilopascals [1], while Environment Canada's standard unit of pressure is the same [2] [3]. Environment Canada (EC, legally incorporated as the Department of the Environment under the Department of the Environment Act ( R ) In the weather code, three digits are all that is needed; decimal points and the one or two most significant digits are omitted: 1013. 2 mbar or 101. 32 kPa is transmitted as 132; 1000. 0 mbar or 100. 00 kPa is transmitted as 000; 998. 7 mbar or 99. 87 kPa is transmitted as 987; etc. The highest sea-level pressure on Earth occurs in Siberia, where the Siberian High often attains a sea-level pressure above 1032. Siberia (Сиби́рь Sibir) is the name given to the vast region constituting almost all of Northern Asia and for the most part currently serving The Siberian High is a massive collection of cold or very cold dry air that accumulates on the Eurasian terrain for much of the year 0 mbar. The lowest measurable sea-level pressure is found at the centers of hurricanes (typhoons, baguios)

Altitude atmospheric pressure variation

This plastic bottle was closed at approximately 2,000 m altitude, then brought back to sea level. It was crushed by air pressure.

Pressure varies smoothly from the earth's surface to the top of the mesosphere. This article is about the atmospheric mesosphere for the Earth's mantle see Mesosphere (mantle. Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. The following is a list of air pressures (as a fraction of one atmosphere) with the corresponding average altitudes. The table gives a rough idea of air pressure at various altitudes.

Calculating variation with altitude

See also: Barometric formula

There are two different equations for computing the average pressure at various height regimes below 86 km (or 278,400 ft). The barometric formula, sometimes called the exponential atmosphere or Isothermal Atmosphere, is a Formula used Equation 1 is used when the value of standard temperature lapse rate is not equal to zero and equation 2 is used when standard temperature lapse rate equals zero.

Equation 1:

Equation 2:

where

P = Static pressure (pascals)

T = Standard temperature (kelvins)

L = Standard temperature lapse rate (kelvins per m)

h = Height above sea level (meters)

R ^* = Universal gas constant: 8. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working 31432×10³ N·m / (kmol·K)

g₀ = Gravitational constant (9. 80665 m/s²)

M = Molar mass of Earth's air (28. 9644 g/mol)

Or converted to English units:^[4]

where

P = Static pressure (inches of mercury)

T = Standard temperature (kelvins)

L = Standard temperature lapse rate (kelvins per ft)

h = Height above sea level (feet)

R ^* = Universal gas constant (using feet and kelvins and gram moles: 8. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this 9494596×10⁴ kg·sq ft·s^-2·K^-1·kmol^-1)

g₀ = Gravitational constant (32. 17405 ft/s²)

M = Molar mass of Earth's air (28. 9644 g/mol)

The value of subscript b ranges from 0 to 6 in accordance with each of seven successive layers of the atmosphere shown in the table below. In these equations, g₀, M and R^* are each single-valued constants, while P, L, T, and h are multivalued constants in accordance with the table below. (Note that according to the convention in this equation, L₀, the tropospheric lapse rate, is negative. ) It should be noted that the values used for M, g₀, and R ^* are in accordance with the U.S. Standard Atmosphere, 1976, and that the value for R ^* in particular does not agree with standard values for this constant. The US Standard Atmosphere is a series of models that define values for atmospheric Temperature, Density, pressure and other properties over ^[5] The reference value for P_b for b = 0 is the defined sea level value, P₀ = 101325 pascals or 29. 92126 inHg. Inches of mercury, inHg or "Hg is a measuring unit for Pressure. Values of P_b of b = 1 through b = 6 are obtained from the application of the appropriate member of the pair equations 1 and 2 for the case when h = h_{b + 1}. :^[5]

Local atmospheric pressure variation

Hurricane Wilma on 19 October 2005 – 88. Hurricane Wilma was the most intense hurricane ever recorded in the Atlantic basin. Events 202 BCE - The Battle of Zama results in the defeat of Carthage and Hannibal. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. 2 kPa in eye

Atmospheric pressure varies widely on Earth, and these changes are important in studying weather and climate. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of See pressure system for the effects of air pressure variations on weather. A pressure system is a region of the Earth's atmosphere where air pressure is unusually high or low

Atmospheric pressure shows a diurnal (twice-daily) cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with amplitude of a few millibars, and almost zero in polar areas. These variations have two superimposed cycles, a circadian (24 h) cycle and semi-circadian (12 h) cycle.

Atmospheric pressure based on height of water

Atmospheric pressure is often measured with a mercury barometer, and a height of approximately 760 mm (30 inches) of mercury is often used to teach, make visible, and illustrate (and measure) atmospheric pressure. History The first barometer is thought to have been built unintentionally by Gasparo Berti, sometime between 1640 and 1643 Inches redirects here To see the Les Savy Fav album see Inches. However, since mercury is not a substance that humans commonly come in contact with, water often provides a more intuitive way to conceptualize the amount of pressure in one atmosphere. Water is a common Chemical substance that is essential for the survival of all known forms of Life.

One atmosphere (101. 325 kPa or 14. 7 lbf/sq in) is the amount of pressure that can lift water approximately 10. 3 m (33. 9 ft). Thus, a diver at a depth 10. 3 meters under water in a fresh-water lake experiences a pressure of about 2 atmospheres (1 atm for the air and 1 atm for the water). This is also the maximum height to which a column of water can be drawn up by suction. Suction is the flow of a fluid into a partial Vacuum, or region of low pressure

Low pressures such as natural gas lines are sometimes specified in inches of water, typically written as w. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, c. (water column). A water column is a conceptual column of water from surface to bottom sediments A typical gas using residential appliance is rated for a maximum of 14 w. c. which is approximately 0. 5 PSI.

Non-professional barometers are generally aneroid barometer (Figure 3) or strain gauge based. History The first barometer is thought to have been built unintentionally by Gasparo Berti, sometime between 1640 and 1643 A strain gauge (alternatively strain gage) is a device used to measure the strain of an object See Pressure measurement for a description of barometers. Many techniques have been developed for the measurement of Pressure and Vacuum.

Atmospheric pressure's relation to water's boiling point

Although water is generally considered to boil at 100° C (212° F), water actually boils when the vapor pressure is equal to the atmospheric pressure around the water. ^[6] Because of this, the boiling point of water is decreased in lower pressure and raised at higher pressure. This is why baking cookies at altitudes beyond 3,500 feet above sea level requires special baking directions. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface ^[7]

See also

• Plenum
• NRLMSISE-00
• Barometric formula
• International Standard Atmosphere - a tabulation of typical variation of principal thermodynamic variables of the atmosphere (pressure, density, temperature etc. NRLMSISE-00 is an Empirical, global model of the Earth's atmosphere from ground to space The barometric formula, sometimes called the exponential atmosphere or Isothermal Atmosphere, is a Formula used The International Standard Atmosphere (ISA is an atmospheric model of how the Pressure, Temperature, Density, and Viscosity ) with altitude, at mid latitudes.

References

1. ^ IUPAC. org, Publications, Standard Pressure (20 kB PDF)
2. ^ Compressor. co. za, May 2003 Newsletter
3. ^ Sample METAR of CYVR Nav Canada
4. ^ Mechtly, E. A. , 1973: The International System of Units, Physical Constants and Conversion Factors. NASA SP-7012, Second Revision, National Aeronautics and Space Administration, Washington, D. C.
5. ^ ^{a b} U.S. Standard Atmosphere, 1976, U. S. Government Printing Office, Washington, D. C. , 1976. (Linked file is very large. )
6. ^ Vapor Pressure
7. ^ Crisco® - Articles & Tips - Cooking Tips - High Altitude Cooking

• US Department of Defense Military Standard 810E
• Burt, Christopher C. , (2004). Extreme Weather, A Guide & Record Book. W. W. Norton & Company ISBN 0-393-32658-6
• U. S. Standard Atmosphere, 1962, U. S. Government Printing Office, Washington, D. C. , 1962.

External links

• NASA page on the 1976 Standard Atmosphere
• Source code and equations for the 1976 Standard Atmosphere
• A mathematical model of the 1976 U.S. Standard Atmosphere
• Calculator using multiple units and properties for the 1976 Standard Atmosphere

Experiments

• An exercise in air pressure
• Movies on atmospheric pressure experiments from Georgia State University's HyperPhysics website - requires QuickTime