On some new features of semiannual variation of the geomagnetic field

Computations from magnetic data restricted to daylight hours were analyzed to estimate the semiannual component of the field with an improved signal to noise ratio. It is shown that this component is entirely equinoctial and that no axial mechanism is observed. Singularities are confined to periods of peak solar activity. The nature of the semiannual component also suggests an association with the preponderance of activity in the northern solar hemisphere over the southern hemisphere.