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Disturbance Daily Variation of the Earth-Currents at Kakioka
The daily variation on quiet days, Sq, of the earth-currents at Kakioka for a 11-year period, 1934-1944, were formerly summarized in the Report of the Kakioka Magnetic Observatory(1). In the present paper, some characteristics of the disturbance daily variation, SD, of the earth-currents for the same period are given, as follows :
i) In the mean values SD and SA=S-Sq computed for the whole period，there is remarkable secondary minimum at 10h (Fig.1). The two values are coincident each other in phase, but the amplitude of the latter is about 40% of the former.
ii) The change of the amplitude of SA(or SD) with seasons and years is remarkable in the diurnal component, but not clear in the semi-diurnal component(Figs. 2 and 4). The appearance of a secondary minimum at 10h may be uncertain at equinox and sunspot-maximum year, because of the predominant diurnal component in the same period.
iii) Our result in (i) differs from the well-known conclusion(2),(4) that the SD in earth-currents is materially a single wave (diurnal one) as in earth-magnetism. Then, the mean SA at Tucson for the period 1932-1942 is computed (Fig. 3). As it is seen in the figure, especially in the vector diagram, departures from the diurnal variation in the hours 12h-18h and 3h-7h are remarkable.Again, the result at watheroo(2) (after Rooney) shows some departures from diurnal variation.
Generally speaking, the appearance of the secondary minimum is not a local phenomenon at Kakioka, but seems to be of world-wide character. It may be related to the disturbances of short period or duration.
Corrigenda is attached to this text.
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