Heights of Reflection of Radio Waves in the Ionosphere

A general method has been developed whereby, from the virtual height frequency curves, it is possible to calculate an upper limit to the height of reflection of a radio wave of a particular frequency in the ionosphere. The various portions of the ionosphere are considered as belonging to one of three groups; first, those in which the electron concentration increases continuously with altitude, the manner of increase being unknown at the start but appearing as a result of the calculations, second, those portions in which the concentration remains essentially constant over an appreciable thickness and, third, those portions for which the concentration is less than the maximum of the region immediately below. It was found that a discontinuity in a virtual height frequency curve is a necessary but not a sufficient condition for the existence of two distinct layers. When the method was applied to a particular time and place, it was found that, whereas some of the $F_2$ virtual heights were rising during the morning hours, the true heights were falling.