The diurnal variation of the ionospheric absorption of wireless waves

Experimental determinations of the reflection coefficient of wireless waves reflected from the F region of the ionosphere are described. The afternoon variation of the reflection coefficient was investigated on several days between June and December 1936. Days with a quiet ionospheric behaviour were chosen, and the tests made in choosing such days are described. The results can be explained on the assumption that the absorption occurs in the lower portion of a simple E region of the type considered by Chapman. It is shown that the recombination coefficient must be independent of the pressure at heights above 110 km. at least, and that it must have a value not less than 10 -8 . It is pointed out that this value does not fit in with the usually accepted theory. The absorption measurements are shown to be in agreement with Martyn's 11 suggestion that the collisional frequency for electrons in the neighbourhood of the E region is given by assuming that the value at a height of 90 ± 5 km. is 10 6 per second and that the scale-height of the atmosphere is 9 km.