196 



ANNUAL REPORT SMITHSONIAN INSTITUTION,, 1942 



the ionosphere permits interpretations of variations in the earth's mag- 

 netism and of radio communications. 



The programs of ionospheric research, which are incorporated 

 with the other scientific investigations at the observatories of the 

 Department of Terrestrial Magnetism of the Carnegie Institution of 

 Washington near Huancayo (Peru), Watheroo (Western Australia), 

 and College (Alaska), and of the National Bureau of Standards near 

 Washington, supplement our understanding of normal as well as 

 abnormal relationships between the sun and the earth. Among the 

 more normal relationships is the effect of sunspots upon the iono- 

 sphere. This is illustrated by the average relationship that large 



"3S7" 



1927 



A-' 





N 



SUNSPOT-NUMBei> ~ 



.ELCCTRON' DCNSI T r 



HfiO0fiO0\ 



\ 



\ 



FIG. —COMPARISON OF ANNUAL AVERAGE SUNSPOT-NUMBER 

 WITH ANNUAL AVERAGE ELECTRON-DENSITY OF F^-RECION 

 MEASURED AT NOON AT HUANCAYO MAGNETIC OBSERVATORY, 

 PERU 



Figure 10. — Comparison of annual average sunspot numbers with annual average 

 electron density of Fa-region as measured at local noon, Huancayo Magnetic 

 Observatory, Peru. 



numbers of sunspots are in general associated with large numbers of 

 electrical charges in the earth's outer atmosphere. The average an- 

 nual maximum density of electrons at noon as measured in the region 

 of the highest layer at the equatorial station of Huancayo follows 

 the annual averages of sunspot numbers — from minimum to maxi- 

 mum of sunspots the change of average annual ion density is about 

 one to three. The two lower regions show changes, similar in form, 

 but of smaller magnitude, with an increase in density only by some 

 50 percent. The geomagnetic diurnal variation changes in value by 

 some 50 percent from minimum to maximum of sunspot activity. 

 This corresponds under like conditions to observed changes in ion 

 density of the two lower regions, but is greatly different from the 

 change of some 300 percent in ion density of the third region. Evi- 



