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Local Field in Geomagnetic Diurnal Variation
Geomagnetic diurnal variation Sq in the vicinity of the focus latitude of the equivalent overhead current system is studied, Z component being taken into consideration. Vector diagrams of diurnal variation in the vertical plane (H-Z plane) are drawn for seasonal mean Sq of 4 observatories, Memambetsu, Kakioka, Kanoya and Chichijima (Fig. 1, T able 1). North-South distribution of general inclination of the vector diagram in H-Z plane gives a good base for determining the focus latitude, as the vertical one must be at the focus. For a single day diurnal variation, northward or southward shift of the focus often occurs, and it is clearly seen in the distribution pattern of the vector diagram (Fig. 2).
A better expression of Sq field in the vicinity of the focus is given by the local time distribution of simultaneous equivalent horizontal current arrows and Z values of the 4 observatories (Fig. 3). Negative center of Z value coincides with the vortex center of the current arrows. Sometimes considerable local fields are founds superposed upon the normal pattern of these distributions (Figs. 4 and 5).
They are not considered to be a kind of known disturbance fields, but seem to be caused by local change of ionospheric wind or conductivity which is the main factor of the dynamo action.
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