Abstract
A study has been made of the lunar variations in heights and critical frequencies of the E, F 1 and F 2 regions above Canberra, Australia. Semi-diurnal lunar variations have been found in all these quantities, and the harmonic coefficients determined. From the study of these it is concluded: ( a ) that ionospheric lunar variations are caused by ionic drift under the action of the ‘dynamo’ electric forces, and not by simple tidal rise and fall of isobaric surfaces; ( b ) that the lunar magnetic variations are not produced in the E, F 1 or F 2 regions.

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