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Time Change of the Geomagnetic Daily Variation at Kakioka, Memambetsu, and Kanoya
The day-to-day change of the geomagnetic daily variation at Kakioka, Memambetsu, and Kanoya is decomposed into several patterns by using the method of the principal component analysis. As a result, the first component represents the fluctuation of the intensity of the Sq-current vortex in the ionosphere, whose amplitude varies in both the annual and 11-year cycle. The cause of this variation is attributed to the fluctuation of dynamo current due to the diurnal tidal wind. The eigenvector of the second component consists of a pair of current vortices on both sides of the noon. which is interpreted as the dynamo current fluctuation associated with the semi-diurnal tide. The third component. whose current pattern and time variation are quite different from those of the leading two components. is probably caused by the ionospheric currents originated in the polar region. The method introduced here can be used for more precise description of the pattern fluctuations of equivalent currents than the analysis on the basis of movements of the Sq foci.
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