A “Fourier Analysis of Residuals” technique was used to determine the monthly average values of the semidiurnal lunar tidal component of the geomagnetic field in the quiet solar-activity year of 1965 for the three orthogonal field components, H, D, and Z. Sixteen stations that were representative of the equatorial, middle, auroral, and polar cap regions of the American sector provided the data for the determination of a latitude distribution of the lunar amplitudes and phases. The annual mean, annual variation, and semiannual variation of the geomagnetic lunar effect were separated. A series of special plots presents the results as a function of latitude in a format that gives the amount of change and month of maximum increase from the annual mean level for both the field amplitude and phase. For H-component amplitudes, the annal variations (about 3.5 gammas) exceed the semiannual variations near the equator and the semiannual variations are largest (about 3.0 gammas) at the auroral latitudes. The annual amplitude variations generally reach a maximum in the months just after the summer solstice. The maxima of semiannual variations occur close to the equinoxes.
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Wallace H. Campbell (1980) studied this question.