Pulse trains with periods of the order of a minute occur in the natural VLF signals emitted in the exosphere. Composed of otherwise ordinary VLF emissions, the long‐period pulses always rise in frequency. At magnetically conjugate points the long‐period pulse signals are received simultaneously. The period of the pulsation events exhibits a latitude dependence, becoming longer at higher latitudes. On the basis of available data, a hypothesis associating hydromagnetic waves with emitting particles is offered to account for the observed properties of the pulsations.

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Data from several Alaskan stations observing the natural VLF electromagnetic radiation known as chorus permit a number of statistical investigations, especially of latitudinal variations of the phenomenon. Maximum occurrence lies at 60° to 70° geomagnetic latitude. Seasonal variations at individual stations depend intricately on latitude. Below, but not above, the auroral zone the diurnal maximum depends on an ‘eccentric geomagnetic latitude.’ Chorus correlates with other phenomena, such as geomagnetic activity, the correlation varying seasonally and diurnally. Correlations between stations show a diurnal behavior consistent with the possibility of the existence of isochronic lines for chorus. Temporal variations in the highest frequency (kilocycles per second) of chorus for each sample show a diurnal minimum near noon and seasonal peaks near equinoxes; temporal variations in the rate of change of frequency of chorus show similar patterns.

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The nose whistler dispersion equation was numerically integrated using the following assumed functions for the electron density distribution: (1)N=K (2) N = KR−3. (3) N = KR−3 exp(3.03/R). N is the electron number density, R is the distance from the earth's center, and K a constant of proportionality. Several whistlers that were received at College on March 19, 1959, were analyzed to obtain electron densities. Each of these whistlers consists of a number of branches having successively lower nose frequencies. Measurements of the nose frequencies and the time of propagation of the nose frequency yield values of the constant K from which the electron density can be determined at any point. It was found that the results for the first two functions disagree systematically with the curve of the assumed function. The third function, suggested by F. S. Johnson on the basis of theoretical considerations, fits the data well within the experimental errors. The resulting distributions cover the range between 4 and 6 earth's radii, giving densities varying from 20 to 5 electrons per cubic centimeter.