164 ANNUAL REPORT SMITHSONIAN INSTITUTION,, 1942 



During tlie last few years of siinspot activity, there have been 

 occasions when remarkable fade-outs have occurred in radio com- 

 munication. In several of these instances extraordinary explosions 

 have occurred on the sun simultaneously with the interruption of all 

 radio communication in general. It would appear that the intense 

 ionizing radiation from the region of the sun where these eruptions 

 occur reaches the earth with the velocity of light and of sufficient 

 intensity to disturb immediately the ionized layer, confusing the 

 reflection of radio waves, and thereby resulting in these fade-outs 

 which sometimes last for an hour or more. Records at magnetic 

 observatories show that during such instances characteristics of the 

 earth's magnetic field are likewise suddenly altered. 



Could we visualize the ethereal substance of the ionosphere as we 

 visualize the surface of the ocean, we should find times when terrific 

 storms were raging in this ionosphere. Here ions and electrons are 

 being hurled hither and yon as through some great electrical wind 

 played upon its surface, creating waves literally miles high. Fre- 

 quently the turbulence attains such proportions that no reflecting 

 surface for radio communication seems possible at all. Wlien dis- 

 turbances on the sun subside, the undulations in the ionosphere may 

 quiet down and there is a return to more normal conditions for com- 

 munication traffic through this ocean of the upper air. 



"\'VTiile knowledge of the sun has helped us to understand the 

 vagaries of radio, we are coming to see that radio is one of the most 

 important tools for learning about what happens on the sun and how 

 disturbances there aff'ect the ions in this upper air. Perhaps some 

 day, even though the slcy is cloudy, we shall have a sufficient number 

 of reports of radio conditions over the globe so that we can form a 

 very good idea as to what is happening on the surface of the sun 

 by the way in which world-wide radio communication behaves. 

 Unlike the telescope, radio apparatus does not go out of commission 

 when the sky is overcast, for electric waves, of course, pass through 

 the clouds as easily as ordinary daylight comes through window glass. 



Concerning the exact method or methods by means of which the 

 sun produces all these electric disturbances of the upper air with 

 the concomitant magnetic variations in the earth, we still lack a 

 great deal of knowledge. The fact that the ultraviolet radiation 

 from the sun is the major factor in producing this ionization appears 

 a reasonable assumption. Whether or not, in addition to the effect 

 of the ultraviolet light, streams of charged particles also emanate 

 from the sun in the regions of sunspots is perhaps still debatable, 

 yet there is accumulating evidence that in addition to the wave radia- 

 tion from the sun there is also a particle radiation that is primarily 

 responsible for the violent magnetic disturbances such as accompanied 

 the marked solar activity of Easter week in 1940. The elaborate 



