PRECIPITATION AFFECTED BY SOLAR VARIATION 



By C. G. abbot 

 Research Associate, Smithsonian Institution 



I published recently a paper entitled "The Sun's Short Regular 

 Variation and Its Large Effect on Terrestrial Temperatures," ^ It 

 showed a perfectly regular variation of the sun's output of radiation, 

 with a period of 6.6456 days. Associated with this, but subject to 

 occasional displacements of phase of i, 2, or rarely 3 days, were tem- 

 perature changes at Washington, St. Louis, and Helena, ranging from 

 2° to 20° Fahrenheit. I was unable to discover the causes of the dis- 

 placements of phase and variations of amplitude in the terrestrial 

 responses to the regular solar period, but averaged over many years 

 the terrestrial effects showed the identical period found in the solar 

 variation. 



It occurred to me to test whether precipitation also responds to the 

 6.6456-day solar period. I did not expect much correlation, because 

 precipitation in most regions is very irregular in amounts and inter- 

 vals. However, a preliminary trial for Peoria, 111., a station which 

 previous studies showed to be largely dominated by solar variations, 

 indicated that the 6.6456-day period is effective on precipitation there, 

 but that phase changes similar to those noted above occur, I then 

 undertook a statistical study of Washington precipitation, from 1924 

 to 1945, with reference to the 6.6456-day period. 



As in the temperature studies, I made separate computations for 

 each month of the year. It proved advisable to recognise the same 

 phase shif tings that I had determined for temperatures. In order to 

 see if the effect occurs at all times, I divided the data into three 

 groups, 1924 to 1930, 1931 to 1937, and 1938 to 1945, All groups 

 showed a considerable effect. To show the procedure, I now refer to 

 figure I , which is a facsimile of my computations for the middle group, 

 193 1 to 1937, for March, I select a March group for illustration be- 

 cause table 3 of my paper (above cited) gives the phase shif tings for 

 March in the temperature work, and I use in all months phase shift- 



1 Smithsonian Misc. Coll., vol. 107, No. 4, Apr. 4, 1947. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 107, NO. 9 



