SOLAR RADIATION AND ATMOSPHERE— STETSON 161 



This region lies far above the stratosphere and generally above the 

 region that is usually regarded as that where ozone is manufactured. 

 This E layer is particularly favorable for reflecting or turning back 

 radio waves of the frequencies which are most generally used for 

 commercial broadcasting in connection with our entertainment pro- 

 grams. Radio waves of much shorter wave lengths or of higher fre- 

 quencies penetrate and actually traverse through this region until they 

 reach what appears to be another ionized region called the F layer, 

 originally postulated by Professor Appleton in England. This F 

 layer lies some 200 kilometers high or in the territory where auroral 

 streamers stage their gorgeous displays. If the ionization of these 

 upper regions is more intense as we near the period of maximum sun- 

 spot activity, one might well expect that some change might be 

 observed in connection with radio transmission. 



Anticipating a new field of research, a Boston radio engineer, G. W. 

 Pickard, and myself became interested in the making of quantitative 

 measurements of radio reception during the sunspot maximum of 1928 

 in an endeavor to discover if such anticipated effects on radio com- 

 munication could be measured. After a few years' observations, it 

 appeared to be evident that when solar activity increased the field 

 strength of a Chicago broadcasting station observed in Boston notably 

 weakened, whereas as sunspots became less numerous there was a 

 marked increase in the intensity of the radio waves from Chicago. 

 A similar investigation carried on during the decline of sunspots from 

 1930 to 1932 between Chicago and the Perkins Observatory of Dela- 

 ware, Ohio, yielded data to indicate that with a decrease of sunspots 

 from a monthly average of 60 at the beginning of 1930 to a monthly 

 average of about 10 in 1932, radio reception increased sixfold in its 

 intensity. 



Continued observations of the Chicago-Boston field strengths in 

 recent years have continued to substantiate the general effect earlier 

 observed. While there may be a 600 percent change in the field 

 strengths between a sunspot maximum and a sunspot minimum, this 

 does not mean that the degree of ionization in the Kennelly-Heaviside 

 layer has been altered by this amount. The field strength of a radio 

 wave at a given distance for a given frequency depends upon the angle 

 of reflection or refraction which in turn is dependent upon the degree 

 of ionization. Field strength also depends upon the absorption of the 

 waves, which is a function of the conductivity. Appleton has esti- 

 mated from his observations that the ionization and the electrical con- 

 ductivity of the E and F regions in passing from sunspot maximum 

 to sunspot minimum have shown variations of 50 to 60 percent imply- 

 ing that the solar ionizing agent (ultraviolet light) responsible foi- the 

 formation of these regions in the ionosphere varies from 120 to 150 

 percent during the sunspot cycle. 



