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 F
1
layer at about 180 kilometers virtual height, and an F
2
layer 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 F
1
layer 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 F
1
layer showed magneto-ionic splitting during the day. There was some correlation between F
1
layer ionization and magnetic storms. The F
2
critical 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 F
2
critical frequency may be determined by some other factor than penetration, such as absorption.