摘要：Long-period electromagnetic response must be estimated to derive information on the electrical conductivity distribution within the deep mantle of the Earth. For this, we estimated the electromagnetic response function for long-period geomagnetic variations, on the basis of the P 1 approximation. The data used for analyses are geomagnetic daily mean values for 10 years (1965–1974) from 59 stations distributed over the globe and for about 20 years (1960–1980) from 9 stations. It turned out that the P 1 approximation generally holds except for the periods corresponding to annual and semi-annual variations. We also found that accurate estimation is difficult for periods longer than a few years, probably because of contamination due to secular variations of core origin.
