422 



Table 136 



TOTAL ANNUAL AND SEASONAL DIRECT RADIATION REACHING THE GROUND 

 WITH VARIOUS ATMOSPHERIC TRANSMISSION COEFFICIENTS 



(Explanation on p. 420.) 



The solar constant Jo is assumed to be 1.94 cal. cm." 2 min." 1 Values apply to a horizontal surface. 



Latitude o° 10° 20° 30° 40° 50° 60° 70° 80° 90° 



Transmission coefficient a = 0.6 



cal. cm.- 2 



41320 29800 25200 



1020 

 42340 29800 25200 



Summer half-year 75710 81630 83570 81830 76120 66830 55000 

 Winter half-year 75710 66430 54280 40510 26330 13680 5000 



Total 151420 148060 137850 122340 102450 80510 60000 



Transmission coefficient a = 0.7 



Summer half-year 93050 99790 102340 100610 94790 84990 72030 

 Winter half-year 93050 82640 68870 53160 36120 20410 8170 



Total 186100 182430 171210 153770 130910 105400 80200 



Transmission coefficient a = 0.8 



Summer half-year 112040 119380 122440 121320 115400 105400 92140 

 Winter half-year 112040 100500 85300 67440 48260 29080 12960 



Total 224080 219880 207740 188760 163660 134480 105100 



Transmission coefficient a = 0.9 



Summer half-year 132650 140710 144580 143870 138360 128660 115810 101220 92440 89890 

 Winter half-year 132650 120190 103660 84490 62950 40820 20210 6940 1020 



Total 265300 260900 248240 228360 201310 169480 136020 108160 93460 89890 



57240 44790 39990 

 2140 110 

 59380 44900 39990 



76630 65100 60610 

 3880 310 

 80510 65410 60610 



Table 137 



OPTICAL AIR MASS CORRESPONDING TO DIFFERENT ZENITH DISTANCES 



OF THE SUN 



The optical air mass m (also called the "air mass") is the length of the atmospheric 

 path traversed by the sun's rays in reaching the earth, measured in terms of the length 

 of this path when the sun is in the zenith. For a zenith distance z of the sun less than 

 80° the optical air mass is approximately equal to sec. z. At greater zenith distances the 

 secant gives values which are increasingly too high, because of errors due to atmospheric 

 refraction, curvature of the earth, etc. Table 137 is based on the widely used computa- 

 tions of Bemporad, 1 who gives the formula 



atmospheric refraction in seconds 



1 Bemporad, A., Rend. Ace. Lincei., Roma, ser. 5, vol. 16, pp. 66-71, 1907. See also Linke, F. 

 Handbuch der Geophysik, Band VIII, pp. 240-245, Gebriider Borntraeger, Berlin-Zehlenday, 1943. 



SMITHSONIAN METEOROLOGICAL TABLES 



