438 Table 148 



SPECTRAL DISTRIBUTION OF SOLAR RADIATION AT SEA LEVEL 



Using Fowle's * data for scattering of solar radiation by water vapor and by air, Moon 3 

 calculated the spectral transmission factors at sea level with 20 mm. of precipitable water 

 vapor in the atmosphere. By comparing these with the mean values of observed trans- 

 mission, he calculated a spectral transmission for dust. 3 He also evaluated the extra- 

 terrestrial solar radiation (see Table 130). 



By combining the extraterrestrial solar radiation with the scattering by water vapor, 

 air, and dust, and with the absorptions by water vapor and ozone, Moon calculated the 

 solar radiation which reaches sea level for various optical air masses (see Table 137 for 

 corresponding solar altitudes). The data were computed for a pressure of 1 atmosphere 

 on the basis of arbitrary average values of water vapor, dust, and ozone content. These 

 values are : 



water vapor, 20 mm. precipitable water, 

 dust, 300 particles cm. -3 near the ground, 



n7nnp 9 R mm riotVi IpncrtTi ^t \T T P 



ozone, 2.8 mm. path length at N. T. P. 

 The results given here have been adjusted to a solar constant of 1.94 cal. cm." 2 min." 



Optical air mass 



Optical air mass 



Wave 

 length 



H 



cal. cm.- 2 min. -1 



0.29-0.40 0.0S9 0.029 0.015 0.008 0.004 



0.40-0.70 .616 .481 .379 .302 .240 



0.70-1.1 .454 .393 .343 .301 .266 



1.1 -1.5 .140 .103 .084 .071 .060 



1.5 -1.9 .075 .066 .060 .056 .052 



1.9 -00 .019 .014 .011 .010 .009 



Total 1.363 1.086 0.892 0.748 0.631 



1 Fov/le, F. E., Smithsonian Misc. Coll., vol. 69, No. 3, 1918. 



2 Moon, P., Journ. Franklin Inst., vol. 5, p. 583, 1940. 



3 This assumes that 20 mm. of precipitable water vapor was representative of these observed trans- 

 missions, which may not have been the case. Any error so introduced would be small, however. 



Table 149 



TOTAL SOLAR AND SKY RADIATION ON A HORIZONTAL SURFACE DURING 



CLOUDLESS CONDITIONS 



Klein 1 gives equations which permit the evaluation of the total solar and sky radiation 

 Q on a horizontal surface for a cloudless, dust-free atmosphere as a function of the 

 atmospheric transmission obtained from Kimball's chart (Table 147) and the solar zenith 

 distance. Fritz 2 combined Klein's equations and constructed the chart given below. The 

 isopleths give values of Q in cal. cm." 2 min." 1 as a function of optical air mass m v (abscissa) 

 and precipitable water vapor w centimeters (ordinate), when the sun is at its mean 

 distance from the earth. To correct for the sun's actual distance from the earth, divide 

 the values by the square of the appropriate radius vector (Table 169). For elevated sta- 

 tions, multiply the values given in the chart by />/1013, where p is the barometric pressure 

 in millibars at the place of observation. Dashed lines indicate extrapolated values. 



indicate extrapolated values. 



"Klein, W. H., Journ. Mcteorol., vol. 5, p. 119, 1948. 



2 Fritz, S., Heating and Ventilating, vol. 46, p. 69, 1949. 



(continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



