PPL » Meteorology » Atmospheric Pressure and Density
8.10 Atmospheric Pressure and Density
8.10.2 Define ‘atmospheric pressure’.
- The atmospheric pressure is a measure of the weight (force) of the air above the surface of the earth in a unit area.
- at sea level has a mean value of 1013.25 hectopascals (roughly 14.7 psi).
8.10.4 State the pressure units used in New Zealand aviation.
Pascal – Pa.
When measuring the pressure at the earth’s surface we use the unit hectopascal (hPa).
101,300 Pa = 1013 hPa. (100 Pa = 1 hPa)
8.10.6 State the significance of air pressure to aviation.
The changes of air pressure day to day can;
- affect aircraft and engine performance.
- Higher pressure = better performance
- Lower pressure = poorer performance
- affect the weather, changes in
- stability of air
- affect aircraft instruments
- altimeter readings
8.10.8 Define ‘pressure lapse rate’.
Change of Pressure with Height
- The Pressure Lapse Rate is the rate at which pressure changes with height in the Atmosphere.
- As height is gained, the amount (weight) of air above decreases and the pressure therefore decreases.
- In a warm column of air,
- particles are far apart,
- column of air will have greater height,
- fall off of pressure will be slower,
- i.e. 1 hPa/40 feet.
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