Averages of critical frequencies and virtual heights of the ionosphere, observed by the National Bureau of Standards at Washington, D.C., April to June, 1940

Abstract

The following ionosphere data are in continuation of those published in this Journal and in each issue subsequently.The data given here are in part somewhat different from those presented graphically each month in Proceedings of the Institute of Radio Engineers, because those are for undisturbed days while these are for all days of the month.