A hypothetical vertical distribution of temperature, humidity, and pressure taken to be representative. Used for aircraft altimetry, engineering design, etc. The particular standard atmosphere used is the U. S. S. A., equivalent to the ICAO standard atmosphere (Reference 15).
A standard atmosphere has been defined by the International Civil Aeronautical Organization (ICAO). It assumes a mean sea level temperature of 15°C a standard sea level pressure of 1,013.25 millibars or 29.92 inches of mercury, and a temperature lapse rate of 0.65°C per 100 meters up to 11 kilometers in the atmosphere.