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.