Abrupt Change in Secular Variation Rate of Geomagnetic North Component Observed in Japan

Abstract

Variation in the annual mean value of the north component of the earth's magnetic field from 1964 to 1976 at the Kakioka Magnetic Observatory is examined in relation to variation in sunspot number. From 1966 to 1973, the annual mean value has shown a decrease at a nearly uniform rate of about 8 nT/year with slight fluctuation from which the influence of solar activity on the field may be estimated. At 1965.5 and in 1974, remarkably large accelerations have taken place which differ considerably from the values expected from the above estimated solar cycle effect. From 1974.5 the annual mean value began to increase at a rate of more than 10 nT/ year which is also perturbed by the solar cycle effect. Such abrupt changes in secular variation rate with a time scale of one year or so seem to be worth noting and might be one of the fundamental characteristics of secular variation if it is confirmed by more detailed analysis that it originates in the earth's interior. © 1980, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.