IRoebliuG fxxn^ 



SUN SPOTS AND WEATHER 

 By C. G. abbot 



Secretary, Smithsonian Institution 



I wish to present evidence pointing to four major conclusions 

 regarding weather, as follows : 



1. The principal departures from normal climates which comprise 

 " weather " are due primarily to a group of periodic variations of the 

 sun's radiation rather than to terrestrial complexities, as has been 

 generally supposed. 



2. Sun spots are associated with important modifications of weather 

 not hitherto recognized. 



3. Important periodicities in solar variation have their least com- 

 mon multiple in 23 years. As a consequence, weather repeats itself in 

 all parts of the world with 23-year intervals. This period agrees with 

 Hale's discovery of the double sun-spot period cycle in the magnetic 

 condition of the sun. 



4. At many stations this cycle in weather enables us to forecast 

 general conditions of temperature and precipitation for many years 

 in advance. Accurate seasonal predictions would require a more com- 

 plete knowledge of the causes of shifts of phase in weather perio- 

 dicities than is yet available. 



A. ASSOCIATED SOLAR AND TERRESTRIAL PERIODICITIES 



During the past year Mrs. A. M. Bond and I have been studying 

 the departures from normal monthly temperatures for several stations 

 in the United States. We have derived our data from " World 

 Weather Records," ' and its continuation to 1930, now in galley proof 

 at the Smithsonian Institution. In order to avoid confusion we have 

 eliminated short-interval fluctuations by taking running 5-month 

 means.^ This device, of course, greatly reduces the amplitudes of the 



* Smithsonian Misc. Coll., vol. 79, 1927. 



^ If a, b, c, d, e, f, are values, substitute for c and d — — — — — — — — — , 



b + c-t-d-fe-f-f ^^^ 



5 



Smithsonian Miscellaneous Collections, Vol. 87, No. 18 



