On two methods of ionospheric investigation

Two wireless methods of measuring upper-atmospheric ionization, both of which involve measurements of the equivalent height of reflection for a number of electric wave frequencies, are described. Different relations are expected and found to exist between the equivalent height and the frequency for the ordinary and extraordinary magneto-ionic components. From the examples chosen to illustrate the methods the following deductions and measurements concerning ionospheric characteristics are made. (a) Magneto-ionic double refraction is caused by region E; this shows, as was previously demonstrated in the case of region F, that free electrons are the effective electrical agents. (b) For daytime conditions, and more frequently in summer than in winter, evidence of the existence of a protuberance or "ledge" on region F is found, which most probably indicates that under direct solar influence this region is sometimes composite. Evidence of the existence of ionization between regions E and F ("intermediate region") has also occasionally been obtained at noon so that the whole ionospheric configuration may be regarded as a composite structure of four components. From the point of view of practical radio communication, however, it is sufficient to regard the ionosphere as divisible into two main regions, E and F, but where it is necessary to consider further the ionospheric fine structure it is proposed to name the four components, at successive increasing equivalent heights, regions E^I, E^II, F^I and F^II. Usually only regions E^I and F^II are of importance. (c) The rate of decay of region-F ionization during the night has been measured and found not to be explicable in terms of the simple law of recombination between ions and electrons. (d) Measurements have been made of the rate of production of electrons in region F during the period following sunrise.