Theory of lunar effects and midday decrease in F2 ion‐density at Huancayo, Peru

It is shown that the diurnal variation of the earth's magnetic field gives rise to forced diffusion of ions in the F2 region. Calculations indicate that at Huancayo, Peru, this diffusion may account for the midday decrease in F2 critical frequency observed there. To test this theory, the F2 data from Huancayo were examined to determine if, when the solar and lunar magnetic diurnal variations are in phase, the midday values of F2 critical frequency are lower than when the variations are out of phase, as called for by the theory. The predicted effect was verified by the observations.