Studies of the Ionosphere and Their Application to Radio Transmission

An historical summary is presented which outlines the principal published reports of studies of the ionosphere applied to radio wave propagation. Observations of the virtual height of the ionosphere and its variations carried out at the Bureau of Standards during the period of September, 1930, to April, 1933, are reported and discussed. The pulse method of Breit and Tuve was used with a visual recording technique developed by the Bureau of Standards. In general, a number of layers were discernible, the major daytime layers being the lower or E layer at about 100 to 120 kilometers virtual height, an F1layer at about 180 kilometers virtual height, and an F2layer at about 240 kilometers virtual height. The relative electron densities of these layers were determined by measuring the critical penetration frequencies where possible. The E and F1layer critical frequencies were highest at summer noon and fell off both diurnally and seasonally as the angle of the sun's rays with the vertical increased. Abnormally strong E layer ionization occurred occasionally at irregular intervals. The F1layer showed magneto-ionic splitting during the day. There was some correlation between F1layer ionization and magnetic storms. The F2critical frequency was greatest on a summer evening, and greater on a winter noon than on a summer noon. From this evidence it is believed that the F2critical frequency may be determined by some other factor than penetration, such as absorption.