Letter

Abstract

I agree with Prof. Liang about the desirability of plotting F₂-layer critical frequencies with magnetic latitude rather than with magnetic dip. In an article in Science, p. 17, July 4, 1947, I have given such a plot, which, for noon values of equinox critical frequency, shows two sharp maxima at ±18° magnetic latitude. The high midnight values of F₂-layer critical frequency at stations on the geomagnetic equator are also attributed to the low electron recombination which is associated with the marked bifurcation of the F₂-layer into the F₁ and F₂ strata.