346 TABLE 342.— STANDARD ATMOSPHERE (concluded) 



Up to the lower limit of the isothermal atmosphere ( — 67° F corresponding to 35,332 ft) 

 the temperature is assumed to decrease linearly according to the equation 



T = To - ~ h 

 ah 



Further, the atmosphere is assumed to be a dry perfect gas that obeys the laws of Charles 

 and Boyle, so that the mass density corresponding to the pressure and temperature is 



P T, 



i = po — 



The pressure and altitude are related by 



p = po 



po 1 



pa T m p 



h = =- log. — 



p»y i o P 



The harmonic mean temperature T m is given by 



ZAft . A/h + Ah 2 + • • • 



T m = Sry Ah_" Ahi + Ah 2 + •■■ 



Zj T. r T.« Tov, 



where Tun, T aV 2, . . . are the average temperatures for the altitude increments Ahi, A^, • • • 

 The NACA Special Subcommittee on the Upper Atmosphere, at a meeting on June 24, 

 1946, resolved that a tentative extension of the standard atmosphere from 65,000 to 100,000 

 feet be based upon a constant composition of the atmosphere and an isothermal tempera- 

 ture which are the same as standard conditions at 65,000 feet. This tentative extended 

 isothermal region (Table 344) ends at 32 kilometers (approximately 105,000 ft). It is 

 possible that as results of higher altitude temperature soundings become available and the 

 standard atmosphere is extended to very high altitudes the present recommendations may 

 be modified. 



The Subcommittee also recommended that the values of temperature given in the follow- 

 ing table be considered as maximum and minimum values occurring for the given altitudes 

 with the variations between the specified points to be linear : 



Temperature (°C abs) 

 Altitude 



(km) Minimum Maximum 



20 180 250 



25 — 250 



45 200 380 



A tentative extension of the standard atmosphere computed from the equations using 

 the recommended isothermal temperature and constant gravity altitudes from 65,000 to 

 100,000 feet are included in the table. Calculations have been made 1SS by assuming that 

 the acceleration of gravity varies inversely as the square of the distance from the center 

 of the earth. Up to 100,000 feet this assumption does not greatly affect the tabulated values. 



SMITHSONIAN PHYSICAL TABLES 



