A discussion of the non-cyclic variation field pattern. The field is mainly zonal about the geomagnetic axis, though there are significant departures from axial symmetry. The zonal part corresponds closely to a uniform field plus a dipole field along the geomagnetic axis. The relative values of these two parts accord well with the assumption that the internal part arises from currents induced in the earth by Dst variations. The relationship between the non-cyclic variations and hourly values of equatorial Dst is discussed.
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