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FORECASTS OF SOLAR VARIATION 



By C. G. abbot, 

 Secrrlary, Siiiitlisfliiian Institution 



In my ])aper entitled " Weather Dominated by Solar Changes," ' I 

 showed that the variation of monthly mean values of the radiation of 

 the sun, apparently irregular, is really comprised of a small number 

 of regular periodicities. From the analysis of a preliminary series of 

 solar-constant values, extending from July 1918 to December 1930, I 

 discovered and evaluated five periodicities of 8. ii« 25, 45, and 68 

 months, respectively. The curve constructed as their summation fitted 

 the curve of observation so closely that in November 1930 I ventured 

 to predict the march of the variation of the sun to the end of December 

 1932. This prediction is given as curve T, Figure 3, of the publication 

 cited. 



Monthly mean values of the solar constant of radiation of a pre- 

 liminary character are now available to test this long-range forecast up 

 to December 1932. They have been computed from the daily tele- 

 graphic reports received by the Smithsonian Institution from distant 

 solar observing stations. From January 1931 to the end of May 1932, 

 they represented Montezuma, Chile, alone. Owing to the volcanic 

 eruption in southern Chile, Montezuma values since that time are not 

 as yet available, though they will be later on. The remaining months 

 up to and including February 1933, used in this paper, are taken from 

 observations reported from Table Mountain, Calif. 



In Figure i, I give in the full curve the prediction made in Novem- 

 ber 1930 and in the dotted curve the march of the values of observa- 

 tion. At the time the forecast was made the solar-constant values for 

 several years had been nearly all the time below the normal value, 1.940 

 calories per square centimeter per minute. The prediction indicated 

 an expectation of values continuously above normal, and rising, indeed, 

 to the highest levels observed since iq2i. The event closely verified the 

 forecast in both of these respects. The average deviation between 

 expectation and observation is 0.0058 calorie, or 0.3 of i per cent. The 

 forecast averaged a little too high. 



Smithsonian Misc. Coll., vol. 85, no. i, 193 1. 



Smithsonian Miscellaneous Collections, Vol. 89 No. 5 



