Table 695 

 THE EARTH'S ATMOSPHERE 



Standard Atmosphere 



559 



A standard atmosphere is denned by an altitude-temperature-pressure relation. It is an 

 aeronautic necessity in evaluating the performance of airplanes and for the calibration of 

 instruments. The following standard has been officially adopted by the Army Air Corps, 

 Bureau of Standards, National Advisory Committee for Aeronautics, and the Weather 

 Bureau. However, in the evaluation of flights made to break international records, the 

 Federation Aeronautique Internationale Standard Atmosphere is used. The altitude-tem- 

 perature assumption is a slight modification of that proposed by Toussaint and closely 

 approximates the average observed values of air temperature at all altitudes at latitude 40 

 in the United States. Adapted from M 78 (Brombacher) published by the Bur. Standards. 

 The formulae defining this standard atmosphere follow: 



Z = standard altitude. Z 66 = altitude lower limit isothermal layer. 



T = absolute temperature of air at altitude Z. 



To = standard sea-level temperature, 288° absolute, 15 C. 



T m = mean absolute temperature of air column below altitude Z. 



T m& s = ditto for Z 55 , 251.378° absolute. 



p = air pressure at altitude Z. p , standard sea-level pressure, 760 mm. 



p = density air at altitude Z. p , ditto sea-level, 1.2255 kg/m 3 . 



Z = (KT m /T ) \og 10 (po/p). K is 19,413.3 for Z in meters, or 63,691.8 in feet. 

 p = poip/po) (To/T). 



(1) Up to the isothermal layer (below 10,769 m): 

 T = 288 - aZ. T m = aZ/\og e [T /(T - aZ)]. 



a = 0.0065000 for Z in meters; 0.0019812 in feet. 



(2) At the lower limit of the isothermal layer (10,769 m): 



T = 218° absolute or — 55°C. Z 65 = 35,322 feet or 10,769 meters. 



(3) In the isothermal layer (above 10,769 meters): 

 T m = Z/[Zs,/T mSS +(Z - Z 66 )/2i8]. 



(See Nat. Adv. Comm. Aeronautics Techn. Rep., Nos. 147, 218, and 246 of the committee 

 for further data and complete tables.) 



Smithsonian Tables 



