Multifrequency Ionosphere Recording and Its Significance

Results obtained in hourly measurements of critical frequencies of the layers of the ionosphere are presented for the period of a year between May, 1933, and April, 1934. The critical frequencies were obtained by an automatic recorder which covers the frequency band 2500-4400 kilocycles at a uniform rate of 200 kilocycles per minute. Critical frequencies in this band are for the E and F1layers in the daytime and for the F layer at night. Graphs are presented which represent hourly averages of critical frequencies for each layer for each month. The points from which the averages are obtained are also plotted to show the scatter. The critical frequencies for the E and F1layers follow in phase with the sun both diurnally and seasonally. During the day "fine structure" is often in evidence indicating other strata between the usual E and F1layers. The results obtained for the F layer during the winter night are of particular interest. After dropping to a minimum near midnight the critical frequency increases to a maximum at about 4:00 a.m., then drops to a second minimum before sunrise. This increase during the night represents more than a 100 per cent increase of maximum electron density. The results for the period September 11-30, 1933, are compared with those for the same period of 1934 showing a considerably greater ionization density for the latter period. The minimum point of the average curve for 1934 is about 180 kilocycles higher than that for 1933.