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Figure 2 Pressure altitude versus pressure [2]. The pressure variations for the International Standard Atmosphere can be calculated by using the hydrostatic equation, perfect gas law and the temperature lapse rate equation.
The global mean pressure at the surface of the Earth is PS = 984 hPa, slightly less than the mean sea-level pressure because of the elevation of land. We deduce the total mass of the atmosphere ma: (2.2) where R = 6400 km is the radius of the Earth. The total number of moles of air in the atmosphere is Na = ma/Ma = 1.8x10 20 moles. Exercise 2-1.
observation stations (QFE) above sea level are adjusted for the difference in height to bring them all to a common datum, normally Mean Sea Level (MSL) to enable a chart of pressure distribution to be drawn known as a synoptic chart. The adjusted MSL pressures are known as the QFF, see fig. ME 2.5. Pressure Patterns Revealed by the Isobars are:
The data in Table B.1 define the state variables at sea level (SL) and the gravitational acceleration at 45 northern latitude on which the potential altitude is based. The (absolute) temperature varies linearly in the troposphere between SL and 11 km with a gradient of−6.5 C/km.
This is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea level for locations above or below sea level. The average pressure at mean sea level in the International Standard Atmosphere is 1,013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury.
The atmospheric pressure is the force exerted by the weight of the Earth's atmosphere, expressed per unit area in a given horizontal cross-section. Thus, the atmospheric pressure is equal to the weight of a vertical column of air above the Earth's surface, extending to the outer limits of the atmosphere. 5.1.2 Units
Sea Level Pressure – the pressure that would exist if the observation point were at sea level. Surface Pressure – the pressure observed at. particular location. Equation of State. Ideal gas law p = ρ RT. P = pressure (Pa) ρ = density (kg/m3) T = temperature (K) R = gas constant (287 J/kg k) Pressure Measurement.
