The Ionospheric Eclipse of October 1, 1940

This discussion presents the variations in the critical frequencies of the various ionospheric layers over Queenstown, South Africa, during the total solar eclipse of October 1, 1940, and compares them with the normal-day data. It is shown that recombination and diffusion cannot completely explain the phenomena in the F2layer and that the cooling of the atmosphere by the eclipse may be of major importance. A theory of the formation of the E layer is proposed to account for the observed variations during the eclipse and at night. Minimum values of the apparent recombination coefficients for the E, F1, and F2layers were 1.2·10^-8, 6·10^-9, and 6·10^-11cm.³/electrons per second, respectively. Some of the present data are compared with those, previously unpublished, which resulted from a similar expedition to Kazakstan, U.S.S.R., in 1936.