TheERegion of the Ionosphere

Abstract

Comparison of $E$ region observations from 1930 to 1938 of ionosphere stations scattered over the earth with the theory of ionization caused by solar radiation absorbed exponentially in a relatively quiet terrestrial atmosphere yielded the conclusions: (1) the diurnal variation of $y_m$, the maximum-with-height value of the equivalent electron density, during daylight is in close accord with the theory with the recombination coefficient $\alpha$ proportional to ${y_m}^2$ and equal to 2×${10}^{-8\mathrm{}}$, or perhaps greater; (2) $y_m$ at night was not in accord with the theory, but the data do not preclude a night value of $\alpha =2\mathrm{}\times {10}^{-8\mathrm{}}$ or greater provided suitable hypotheses are added to the theory; (3) the morning increase in $y_m$ was observed at Washington near midsummer to begin about 35 minutes before ground sunrise, whereas the theory put it about 20 minutes; (4) the seasonal variation of noon $y_m$ agrees with the theory at stations in latitudes from 12° S to 80° N; (5) at any season noon $y_m$ falls off with latitude more rapidly than the theoretical expectation. A relation between noon $y_m$ and sunspots is given.