TABLE 63 265 



NACA STANDARD ATMOSPHERE, LOWER ATMOSPHERE 1* 



In 1922 the Weather Bureau at the request of the National Advisory Committee for 

 Aeronautics prepared a "standard atmosphere" 3 for scientific and engineering use based 

 primarily on the average conditions over the United States at latitude 40°. Later Diehl 

 extended the computations to 20,000 meters using constants adopted by the NACA effective 

 January 1, 1925. This atmosphere was based on the assumption of a linear decrease of 

 temperature with height up to the tropopause and an isothermal layer above. In 1935 

 Brombacher 3 prepared additional tables giving alttude as a function of pressure. A tenta- 

 tive extension of the standard atmosphere to 120,000 meters was prepared in 1947 (see 

 Table 68). 



Standard values. — The standard atmosphere is based on approximate absolute tempera- 

 tures, T = 273 + t °C, or for the equivalent absolute Fahrenheit scale T = 459.4 + f °F. 

 since 459.4 + 32 °F. corresponds to 273 "A. Engineering (gravitational) systems of units 

 have been used, the kilogrameter-second, and the pound-foot-second system. The follow- 

 ing standard values have been adopted for use in the definition of the standard atmosphere : 



Metric English 



Standard pressure at sea level p» = 760 mm. Hg. = 29.921 in. Hg. 



Standard temperature at sea level Jo =15 C C. = 59 °F. 



Standard absolute temperature at sea level To =288 °A. =518.4 "Rankine 



Standard isothermal layer temperature 7\ = — 55 °C. = — 67 °F. 



Standard specific weight 4 at sea level gp» = 1.2255 kg. m." 8 = 0.07651 lb. ft." 8 



Standard gravity g = 9.80665 m. sec." 8 = 32.1740 ft. sec." 2 



Standard temperature lapse rate a = 0.0065 °C. m." 1 = 0.003566 °F. ft." 1 



aR = 0.190284 



Standard gas constant for dry air • '. R = 29.2745 = 53.3551 



The standard conversion factors used are: 



1 meter = 3.280833 feet 



1 kilogram = 2.204622 pounds 



Other symbols employed are : 



Z = altitude (see assumption (c) below), 

 T = absolute temperature, 

 Tm = mean temperature (absolute) of the air column, 



p = pressure, 

 M = modulus for the common logarithms = logioe = 0.4342945, 

 Zi = altitude of the base of the isothermal layer, 

 T m i = mean temperature of the air column up to base of isothermal level = 251.378 

 °A = 452.680 ° Rankine, 

 p = specific mass. 



Basic assumptions. — The primary basic assumption is a linear decrease in tempera- 

 ture with altitude 



T = T -aZ (1) 



In addition certain other basic assumptions are necessary to define the standard atmosphere. 

 These assumptions are as follows : 



That (a) the air is dry, 



(b) air is a perfect gas, obeying the laws of Charles and Boyle, i.e., 



p = RgpT (2) 



or 



(*)=(£)(*) 



1 Condensed from Diehl, Walter S., Standard atmosphere— Tables and data, NACA Rep. No. 218, 

 1925. (Often referred to as the U. S. Standard Atmosphere.) 

 3 Gregg, W. R., Standard atmosphere, NACA Techn. Rep. No. 147, 1922. 



3 Brombacher, W. G., Altitude-pressure tables based on the United States standard atmosphere, 

 NACA Rep. No. 538, 1935. 



4 "Density" in absolute system of units. 



5 In Diehl's report the values of aR and R are given as 0.19026 and 29.2708 respectively, but these 

 are not in agreement with the numerical values of the other physical constants given, where R = 

 Po/9PoTo; po here is in kg. m.- 3 . 



* The NACA standard atmosphere has been superseded by the ICAO standard atmosphere. NACA 

 Rep. No. 1235, 1955. (continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



