440 



Table 151 



RELATION BETWEEN AVERAGE SUNSHINE AND SOLAR RADIATION ON A 



HORIZONTAL SURFACE 



Angstrom * has suggested that an equation of the form Q/Qo = a + bS would express 

 the relation between sunshine JT (expressed as a fraction of the possible number of hours) 

 and the ratio of average radiation, Q, on a horizontal surface to the corresponding average 

 radiation, Qo, during cloudless days, where a and b are constants. Fritz 3 determined 

 average monthly values of Qo, by combining computation with an examination of the 

 highest value of radiation recorded at several stations in the United States. These average 

 values of Qo were combined by Fritz and MacDonald 3 with observed averages of the 

 monthly values of Q for 11 stations in the United States for each of which at least 10 

 years of data were available. The plot of the resulting Q/Qo against the corresponding S 

 is given in the scatter diagram below, together with the least square linear regression 

 equation. 4 The correlation coefficient between 5" and Q/Qo is 0.88. 



1 Angstrom, A., Medd. Stat. Met. Hydr. Anst., vol. 4, No. 3, 1928. 



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



8 Fritz, S., and MacDonald, T. H., Heating and Ventilating, vol. 46, p. 61, 1949. 



* The coefficients a and b have also been determined by several other investigators: 



Kimball, H. H., Month. Weath. Rev., vol. 55, p. 157, 1927 22 



Angstrom, A., (reference 1) 235 



Haurwitz, H., Harvard Meteorol. Studies, No. 1, 1934 22-.30 



Mossby, H., Norwegian North Polar Expedition with the Maud, 1918-25, 

 Scientific Results, vol. 1, No. 7, 1932 54 



b 

 .78 

 .765 



.46 



RELATION BETWEEN AVERAGE SUNSHINE AND SOLAR RADIATION ON A 



HORIZONTAL SURFACE 



1.00 



.80 



.60 



0. 



.40 



.20 



- »» .^' * 





•«<••••. • 



§=0.61 



Wo 



.20 



.40 



S 



.60 



.80 



1.00 



SMITHSONIAN METEOROLOGICAL TABLES 



