436 Table 146 (concluded) 



TRANSMISSION OF SOLAR RADIATION BY THE ATMOSPHERE, 5.5-22 M 



Part D. — Average percent transmission in the region 16-19//, and 16-22/t. 3 



Wave-length Precipitable 



interval water Transmission 



li mm. % 



16-19 10 3.3 



16-19 1 14.3 



16-22 1 12.6 



Notes : 



Absorption due principally to H 2 and COa. 



Estimates of transmission in this region are provisional. 



8 Adel, A., Journ. Opt. Soc. Amer., vol. 37, p. 769, 1947. 



Table 147 



TRANSMISSION OF SOLAR RADIATION THROUGH MOIST AIR 



The chart indicates the atmospheric transmission of solar radiation at normal incidence 

 to the sun and was constructed by Kimball * as follows : 



1. The extra-terrestrial relative spectral intensity /ox of sunlight was obtained from 



Abbot. 3 



2. From Rayleigh's scattering law, Kimball computed transmission factors for dry 



air a a \ for the same wave lengths for which h\ were given by Fowle. 



3. To account for scattering of solar radiation by water vapor, Kimball used Fowle's 



water-vapor scattering transmission factors a w \ (see Table 145). 



4. The transmission a' m for optical air mass m and precipitable water vapor w is 



given by 



„/ 2/ox(OaXO«X W )™ f1\ 



2/ox 



where the summation is performed over the range of wave lengths in the solar 

 spectrum. This considers only scattering and not absorption. Curves (l)-(8) 

 (dashed lines) give values of a' m as a function of the optical air mass m. The 

 amount of precipitable water vapor involved in the scattering is indicated on 

 the individual curves. 

 5. With the aid of Fowle's curves showing fractional absorption of solar radiation 

 by water vapor (see Table 140), Kimball computed the effect of absorption and 

 subtracted that from a' m to get the transmission a" m , which thus takes into 

 account absorption by water vapor and dry air as well as molecular scattering. 

 Curves (9)-(15) (solid lines) for a" m are similarly labeled with the amount 

 of precipitable water vapor involved. 



The fraction of energy absorbed by water vapor is given in curve (16) as a function of 

 the product of precipitable water vapor w and optical air mass m. 



1 Kimball, H. H., Month. Weath. Rev., vol. SS, p. 167, 1927; vol. 56, p. 394, 1928; vol. 58, p. 43, 1930. 

 •Abbot, C. G., Smithsonian Misc. Coll., vol. 74, No. 7, 1923. 



(continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



