190 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1931 



PERIODICITIES IN SOLAR VARIATION 



Although the monthly mean variations are apparently irregular, 

 they may be expressed with high correlation as the sum of 5 regular 

 periodicities of 68, 45, 25, 11, and 8 months' interval, respectively. 

 This is the more interesting because 68 and 45 months are respec- 

 tively the half and third of the sun-spot period of lll^ years. 



O" NOV. DEC. JAN. FEB. MAR. APR. MAY JUN. JUL. AUG. SEP. OCT. NOV. DEC. JAN. 

 " Y COMPLETE 12-MONTH CYCLE ■ i^ 



Figure 13. — Spurious 12-montli and real 11-month period in solar-constant observa- 



tion.s since 1920 



Periodicity of approximately 25 months' interval in former centuries 

 has been found by Dr. A. E. Douglass in the growth of trees, and by 

 Dr. Ernst Antevs in the retreat of glaciers. Professor Marvin has 

 claimed that our solar-constant results were affected by a 12-month 

 periodicity, probably terrestrial. Figure 13 shows that he is in error 

 and has mistaken the 11-month periodicity for 12 months owing to 

 having founded his conclusion on insufficient data. 



PERIODICITIES IN WEATHER ASSOCIATED WITH THOSE IN SOLAR 



VARIATION 



• I find that the five periodicities just mentioned and several others 

 of less importance occur in the temperature of stations in the United 



