Memoirs of the Kakioka Magnetic Observatory Vol.15 No.02， p.165, December, 1973

Local Field in Geomagnetic Diurnal Variation

Yanagihara, K.

Abstract

 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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