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A study of geomagnetic storm on the basis of magnetic observations in the Japanese chain observatories
Tsunomura, S., Toya, T., Ishii, Y. & Teshima, S.
Characteristics of geomagnetic storms observed in Japanese chain observatories, Memambetsu, Kakioka and Kanoya are examined on the basis of routine reports, statistics of one-minute magnetic data and a numerical simulation. Stacked records of the one-minute magnetic data for geomagnetic storms starting with SSCs at Kakioka and Memambetsu, show a signature of direct contribution of the ring current in the Z-component for the period of one day or more, although somewhat reduced due to the shielding effect of the Earth's electromagnetic induction. A rough estimation of the ratio of the internal field to the external one using the Hand Z-components for that period range agrees well with that given by Rikitake and Sato (1957). It is imagined that the Z-component at Memambetsu，where the local conductivity anomaly effect is smaller than Kakioka, can be used as one of the realtime monitoring tools to estimate the ring current strength. It was shown that, however, the property of complicated secular variation of the Z-component around Japan should be sufficiently clarified before examining long term variations. Diurnal variation patterns in storm periods were shown in the stacked records dividing to local time blocks of Kakioka. They are possibly attributable to the effect of field-aligned currents and the resulting ionospheric current systems. The variation pattern of the geomagnetic storm of February, 11, 1958, which recorded an extremely large range for the D-component among the geomagnetic storms from the IGY to the present, is briefly examined as a case study. It is shown that the D-component variation associated with a negative bay in the H component just after the SSC contributed to gain the range of the D-component. It is suggested that case studies of geomagnetic storms will remain to be important in future, including the studies for negative bays observed in middle and low latitudes in the noontime.
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