Characteristics of the Ionosphere and Their Application to Radio Transmission

Results of ionosphere measurements near Washington, D.C., made at normal incidence over the period May, 1934, to December, 1936, inclusive, are presented in graphical form as monthly averages for each hour of the day. The general forms of the diurnal and seasonal variations of the critical frequencies and virtual heights have recurred from year to year. In addition to the seasonal variation there has been a continuous long-time increase of critical frequencies which is associated with the eleven-year sunspot cycle. Data are given only for those layers which are fairly regular in behavior-the normal E, F, F1, and F2layers. The interpretation of properties of the ionosphere in terms of radio transmission over medium and long distances is discussed. The properties considered are absorption, virtual height, and critical frequency. It is pointed out that the long-time increase of critical frequencies indicates a corresponding rise in useful transmission frequencies. The paper also describes briefly two types of irregular disturbances of the ionosphere which affect radio transmission.