Open Access

Electromagnetic response of the mantle to long-period geomagnetic variations over the globe

Earth, Planets and Space201450:BF03352160

https://doi.org/10.1186/BF03352160

Received: 9 December 1997

Accepted: 19 May 1998

Published: 6 June 2014

Abstract

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 P1 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 P1 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.