Table 68 (continued) 283 



NACA STANDARD ATMOSPHERE, TENTATIVE PROPERTIES OF THE 

 UPPER ATMOSPHERE 



For combination D (constant temperature gradient and constant volume gradient of 

 dissociation) : 



log-f=C D \og^-§- (12) 



pD 1 D M.D 



where 



C = — gopoToMp ,.~, 



D p (LMo + M D T D K) 



Values of Pa, pn, pc, pD, Tb, and Td can be found in the table corresponding to the 

 appropriate height. T and M may be computed from equations (3) and (4) respectively. 

 The value of M in the region where oxygen is all-atomic is equal to the value of M 

 at the top of the underlying region where dissociation is occurring. 



Speed of sound. — The speed of sound a at any altitude relative to that at sea level ao 

 is computed by the equation 



JL=(W' /2 (14 ) 



where 



ao=(-^) 1/2 (15) 



and the ratio of the specific heats y (=c P /cv, see Table 70) is given by 



7^i 128 K (h-h m ) (l6) 



7o 21 Mo 



Coefficient of viscosity. — Sutherland's equation for the variation of the coefficient of 

 viscosity (j. with temperature is used, 



Hf.)T^#) 



and the value adopted for 5" is 120. The Sutherland formula is strictly applicable only 

 to a gas of constant composition and to pressures which are not too small, and consequently 

 the tabulated values for the kinematic viscosity are obviously not entirely reliable at the 

 higher altitudes. 



Molecular mean free path. — The ratio of the molecular mean free path X at any altitude 

 to the corresponding value at sea level Xo is computed by 



2l-MJ. (18) 



Xo pTogo 



Conversion to true height. — To convert a height h computed on the assumption of 

 a constant value of the acceleration of gravity go = 9.80665 m. sec." 2 to a "true height" 

 H based on the assumption that gravity varies inversely as the square of the distance 

 from the center of the earth the following formula may be used : 



H _ 9.80665 R h (m 



g'o R - 9.80665 h K } 



where g'o is the acceleration of gravity (m. sec." 2 ) at sea level at the latitude in question 

 and R is the radius of the earth in meters. Conversely 



h = 9 '° R H (20) 



9.80665 (R + H) 



Certain second-order terms which are customarily neglected in determining the varia- 

 tion of gravity with height have been neglected in the derivation of equations (19) and 

 (20) ; at very great heights these terms will give rise to small corrections. 



(continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



