340 Tables 89 and 90 



THE COEFFICIENTS /„ AND /, 



(Further explanation on p. 331.) 



Given values of pressure p, temperature t, and relative humidity U, it is necessary first 

 to calculate the corresponding value of mixing ratio r from (1) before attempting to cal- 

 culate those of volume v, enthalpy h, entropy s, and isobaric specific heat c p — all per 

 unit mass of dry air — from (6), (9), (12), and (13), respectively. This obviously re- 

 quires information regarding the saturation mixing ratio r« (p, T) . 



The function /«(£, T) is defined by 



r« = «/.<?„/(£ -/»*,), (14) 



where e»(T) is the saturation pressure of pure water vapor with respect to liquid. It 

 may be well to mention that as pressure p approaches e w (T) from above at any tempera- 

 ture the coefficient /« approaches unity. 



It is frequently necessary in other connections to have information regarding the mixing 

 ratio of moist air at saturation with respect to ice, that is, regarding the function 

 r*(P,T). Similarly, the auxiliary function ft(p,T) is defined by 



r, = €/«<?♦/(/>-/,<?«), (15) 



where d(T) is the saturation pressure of pure water vapor with respect to ice. The 

 coefficient /♦ approaches unity as pressure p approaches ei(T) from above at any 

 temperature. 



The Goff-Gratch formulation includes explicit expressions for the functions ev,(T) and 

 ei(T) (see Tables 94-97). 



Values of the coefficients /« and /< calculated from the Goff-Gratch formulation are 

 listed in Table 89 and Table 90, respectively. Within the ranges covered by these tables, 

 /• lies between 1.0000 and 1.0065 while / t lies between 1.0000 and 1.0089. These departures 

 from unity may be ascribed to three separate though not unrelated effects: (a) the effect 

 of dissolved gases on the properties of the condensed phase, (b) the effect of pressure on 

 the properties of the condensed phase, (c) the effect of intermolecular force (gas imper- 

 fections) on the properties of the moist air itself. While it is true that these departures 

 are small enough to be disregarded in rough calculations, it should be kept in mind that 

 the error thus committed may well exceed the probable error of the saturation pressure 

 data themselves. 



Table 89 



THE COEFFICIENT /„ 



SMITHSONIAN METEOROLOGICAL TABLES 



