Electron density profiles in the ionosphere during the I.G.Y.

In many parts of the world during the last 20 years, regular measurements have been made of the maximum electron density (Nm) and the approximate true height (hm) of the various layers in the ionosphere. Both these parameters can be obtained fairly easily from the h′(ƒ) curves (ionograms) which are produced by automatic pulse-sounding equipment and tabulated values of Nm and hm are generally available. On the other hand, only an extremely small amount of accurate information is available on N(h) profiles, the distribution of electron density with height in the ionosphere, and how these profiles vary with time, season, and geographical location. It follows that very little is known about the variation of N with time at a constant true height [the N(t) curve].