Memoirs of the Kakioka Magnetic Observatory Vol.21 No.02， p.65, March, 1986
Variations in the Nighttime Geomagnetic Total Intensity
Fujita, S., Okamoto, A. & Yoshimori, Y.
Geomagnetic secular variation in Japan relative to Kakioka is intensively investigated using night time geomagnetic total intensity in 1977-1985. One of the important characteristics of the secular variation is that an outstanding oscillatory variation with the period of 4 - 5 years is superposed on the long-term secular variation at the observation points far from Kakioka. This variation occurs by variation of the equatorial ring current intensity with two peaks in one solar cycle. A second one is that effect of ocean currents is important for stations in islands (Hachijo). Finally, it is found that a clear annual variation appears in difference between the night time horizontal intensity of Memambetsu and that of Kakioka.