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Technical Digests---Eclipse Effects in the Ionsphere

01 January 1936

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S a result of pulse measurements made at Deal, New Jersey, during the partial eclipse of the sun February 3, 1935,1 and during the total eclipse of the sun of August 31, 1932,2 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).3 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 observed 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 noneclipse 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.4 The data from which our conclusions were drawn are shown in Fig. 1.