336 Tables 86 and 87 



ENTROPY RESIDUAL OF MOIST AIR 



(Further explanation on p. 331.) 

 The entropy residual As of moist air is denned by 

 *=|i?[log. (77/> 2 / 7 ) - 5.61010] 



+ 4/?(r/«) [log. (T/p 1 /*) + 1.15901] 

 + /?[(r/e) log. (r/e) - (1 +r/«) log, (1+r/e)] 



+ A*, (12) 



where s is the entropy of moist air per unit mass of dry air according to the Goff-Gratch 

 formulation. The constant 5.61010 is the numerical value of log.T ; the constant 1.15901 

 is that of the quantity, eL v (0)/4RT — log e To + \ log. <?« (0), where e v (0) is the satura- 

 tion pressure of water vapor with respect to liquid at °C. In using (12) it is to be 

 understood that absolute temperature is to be expressed in Kelvin degrees and pressure in 

 millibars. 



In Table 86 are listed values of entropy residual As as a function of pressure p, tempera- 

 ture t, and relative humidity U. The entropy of moist air, like its enthalpy, is a relative 

 quantity subject to augmentation by amount A + rB, where A and B are constants that 

 can be disposed of quite arbitrarily. For the present purpose, the residual As has arbi- 

 trarily been assigned the value zero at r = 0, t = °C, p=0; the quantity As/r has 

 arbitrarily been assigned the value zero at r = 00, f = °C, £ = 6.1078 millibars in 

 conformity with the usual steam tables practice. 



Linear interpolation is valid throughout Table 86. Below "C. the dependence of 

 entropy residual on relative humidity is entirely negligible. To aid interpolation, zero- 

 pressure values for dry air (r = 0) are listed in the column U = even though relative 

 humidity is not denned at this pressure (see footnote 5, p. 331). In the region covered by 

 Table 86, the entropy residual lies between —0.00054 and +0.00023 ITcal. "K." 1 (gram 

 dry air)" 1 , which means that it can be safely disregarded in rough calculations. 



The third line of (12) is the so-called mixing entropy s m of moist air per unit mass 

 of dry air. It is a function of mixing ratio only and is represented as such in Table 87 

 since space limitations preclude the tabulation of it as a function of pressure, temperature, 

 and relative humidity at close enough intervals for linear interpolation. 



SMITHSONIAN METEOROLOGICAL TABLES 



