抄録
In order to improve the accuracy of magnetic survey and to clarify the locality of conductivity anomalies of the earth, the variations H, Z and D of geomagnetic daily mean values are examined using the data of 47 magnetic observatories in the world during the period of IGY, 1958. It is clarified as follows. 1) The variations of daily mean values may be caused by the disturbing field due to the ring current around the earth . 2) The coefficients of the geomagnetic potential in the development of spherical functions are shown in (11). The first terms (global effects) of H, Z are proportional to cos θ and sin θ(θ: geomagnetic latitude), and that of D shows rather complicated patterns. The terms up to m = n = 2 except the first term (regional effects) are estimated as 2 % in maximum, comparing with the first term. 3) Excluding the global and regional effects, the local anomalies of H, Z and D are found in Eurasia, South Africa, Melanesia, Oceania and Central America, as shown in Figs. 810. 4) The ratio of the potential coefficients due to the internal and external origins is estimated as 0.27±0.01, because Z'/X' = (0.36±0 .01) tan θ holds. The result coincides with that obtained from the analysis of geomagnetic variations with the period of 27-day. It seems unlikely that the conductivity near the depth of 1, 200 km below Japan is abnormal.
