uo 



RADIATION TUOI.or.Y 



bly due largely to haze variations within the (luulitative specification of 

 a "clear" day and, to a lesser extent, to ozone variations. No ultra- 

 violet variation with sunspots appeared, and if any existed, it was 

 obscured l)y the haze variations. The sunspol numbers for the years 

 H)8() 1941 were 80, 114, 110, 89, ()8, and 48, respectively. There was an 

 ill-defined seasonal variation in K„, which is not brought out in Fig. 3-9, 

 partially attributable to the spring-to-fall decrease in ozone (see Fig. 3-6), 

 in that the ultraviolet intensity was often greater in the autumn than in 

 the spring from equal solar zenith angles. Ho\vever, high En values fre- 

 (jucntly occurred in late winter and early spring which may have been 



150 - 



5 



J- 100 



o 

 o 



V 



^ 



50 60 



AIR MASS M 



Z, degrees 

 Fu;. 3-9. Ultraviolet intensity E,, during clear days in \\ asliiiigtoii. 1937. 

 and Stair, 1943.) 



{Coblentz 



due to unusually clear skies or to local ozone variations attributable to 

 stratospheric weather. 



After 1941 Coblentz and Stair (1944) changed their plan of observation 

 and measured E/,, the ultraviolet energy from the sun and the entire 

 hemisphere of the sky, falling on a horizontal plane, instead of PJ„, the 

 ultraviolet energy from the sun and 22° of the sky, falling on a plane 

 normal to the sunbeams. Values of Eh obtained for clear days in Wash- 

 ington are plotted in Fig. 3-10 as dots, circles, crosses, and triangles for 

 June 4, Sept. 18, and Dec. 21, 1943, and Oct. 17, 1944, respectively. In 

 Fig. 3-10 the two dotted curves outline the spread of value of E„ for clear 

 days in Washington during 193(5 and 1941. Since the points fell in the 

 region between the dotted cur\'es. it was concluded that Eh and A'„were 

 approximately the same; in general, of course, Eh and En cannot be 

 expected to be equal. "N^nlncs of Ei, for .some clear days in high latitudes, 

 obtained (Coblentz el <d., 1912) on a trip to Greenland in 1941 are shown 

 by the solid lines of Fig. 3-10. The increase in Eh with latitude may have 

 been due to less liaze and Ics.s ozone at the higher latitudes, but these 

 features were not measuriMl. 



A series of measurements of Eh for ultra\iolet \\a\e lengths less than 



