SOLAR RADIATION AND ATMOSPHERE — STETSON 



167 



in the E layer. The curve of magnetic disturbance in the earth's field 

 parallels very closely that of transmission disturbances in the F layer. 

 In utilizing field-strength measurements for comparison with cosmic 

 phenomena it has been necessary to apply corrections for the well- 

 known diurnal and seasonal variations which depend upon the extent 

 to which the ionosphere has been illuminated by sunlight during the 

 preceding day. If sucli coi-rection is not op]i]iod, we lii've of co'uvc ;; 



A.VCLE OF SUSS DEPRESSION BELOW THE HORUON 

 >-= , -30^ , -"O" , -S0° , 



FiGtTRE 7. — Curve showing gain of uightly field strengths with the increasing 

 depression of the sun below the horizon based on upward of 8,000 hours of 

 observation. The smoothed curve is used as a correction curve for eliminating 

 seasonal trend before comparing radio field strengths with other cosmic 

 phenomena. 



marked seasonal trend with a minimum of reception conditions in sum- 

 mer and a maximum in winter. The appropriate correction curve has 

 been derived from over 8,000 half-hourly periods of observations, 

 covering a range of — >5° to —70° in the angular depression of the sun 

 below the horizon during the observational periods utilized. 



The possibility that an annual or seasonal change exists that is not 

 allowed for by the changing declination of the sun led to the reexami- 

 nation of all our data of the last few years with the result that a resi- 

 dual annual change apparently exists with a maximum in April and 



