Eclipse Effects in the Ionosphere * 



By J. p. SCHAFER and W. M. GOODALL 



It is concluded from measurements of virtual heights and critical ioniza- 

 tion frequencies of the various regions of the ionosphere which were made 

 during two solar eclipses at Deal, New Jersey, that ultra-violet light is an 

 important ionizing agency in the E, M, Fi, and F2 regions. 



AS a result of pulse measurements made at Deal, New Jersey, dur- 

 ing the partial eclipse of the sun February 3, 1935,^ and during 

 the total eclipse of the sun of August 31, 1932,^ we now have data 

 which show that the passage of the moon's shadow across the earth is 

 accompanied by a decrease in ionization in four of the ionized regions 

 of the ionosphere (E, M, Fi and F2).' 



During the 1932 eclipse the ionic density in the E and Fi regions 

 was found to decrease, with the maximum effect occurring shortly 

 after the eclipse maximum. Since the ionization in these two regions 

 ordinarily changes uniformly with time, and since the variations ob- 

 served during the eclipse were much larger than normal variations, we 

 believe that the decrease in ionic density was actually caused by the 

 eclipse. As regards the changes observed in the F2 region, our 1932 

 results were not conclusive because the maximum effect in this region 

 did not coincide with the eclipse but occurred somewhat later. The 

 ionic density in this region is known to fluctuate on at least some non- 

 eclipse days and did in fact undergo comparable variations on several 

 occasions during the two days preceding and the two days following 

 the eclipse. Other observers have reached the same conclusions as 

 regards the F2 region during the 1932 eclipse from their own data.* 



The data from which our conclusions were drawn are shown in 

 Fig. 1. 



* Presented before joint meeting of I. R. E and U. R. S. I., Washington, D. C, 

 April 26, 1935. Published in same brief form in November, 1935 /. R. E. Proceed- 

 ings as in this Journal. 



» Letter to Nature, vol. 135, p, 393; March 9, 1935. 



* Mention has already been made of the results of our 1932 eclipse experiments 

 in the following publications: 



Science. November 11, 1932; Proc. Fifth Pacific Science Congress, vol. 3, pp. 

 2171-2179, 1934; Nature, September 30, 1933; Bell Lab. Record, March, 1935. 



The data have never been published and we are therefore including some of it 

 in this paper as it may be of interest to other investigators in this field. 



* M refers to the intermediate region between E and Fi. 



" Kirby, Berkner, Gilliland, and Norton. Proc. I. R.E., vol. 22, pp. 2-16-265, 

 February, 1934; Henderson, Canadian Jour. Res., January, 1933. 



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