A semiannual geomagnetic variation that is not dependent on the heliographic latitude effect

Hourly means of the geomagnetic elements recorded at Lerwick have been analysed to determine the effect of monthly sunspot number on the solar and lunar daily variations. The diurnal term of the solar variation in declination is found to have a distinct semiannual component that is independent of sunspot number. Thus this semiannual variation is not generated by the heliographic latitude or axial process proposed by Cortie (1912).