A basic study on the main Geoelectric field

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This two-year project aimed to develop a new research direction in study of the dynamics in the Earth's core. Here we pay special attention to the Geoelectric field that is the Earth's electric field associated with the main magnetic field generated by the geodynamo. The study consisted of two parts and their results will be given in the followings.Part 1. Theoretical study for quantitative evaluation of the Geoelectric field expected by geodynamosIn the previous work, we elucidated the possible relation between the intensity of the toroidal magnetic field at the core-mantle boundary (CMB) and that of relating electric field observed at the Earth's surface. This study also showed that such electric field variations will be of observable strength if a long submarine cable is used for measurement. However the evaluation was made simply without considering the nature of the toroidal field itseld. Within the Earth's core, the toroidal field can only exist as a result of the geodynamo proce … More ss. Therefore in this study, we examined the relation between the toroidal magnetic field and the surface electric field that is expected from a particular dynamo process by a kinematic dynamo simulation. After several case studies, we found that the geoelectric field of observable intensity can be expected for a stable solution of geodynamo.Part 2. Instrumental design and laboratory experimentsIn this study, we designed an instrumentation for attempting to measure the electric field expected by Part 1 of this project in an arbitrary ocean area where a retired submarine cable is not available. Considering the signal expected by theoretical study to noise ratio, it was indicated that the cable length necessary for signal detection was estimated as at least 100 km. According to this estimation, we designed a method to lay a 100 km long cable without using special cable installation vessel. However in this method, we must use electrodes of high quality as the cable length is much shorter than usual submarine cable voltage measurements. For the purpose, an Ag-AgCl electrode was tested which is made of a silver wire corted by silver-chrolide, and compared with other electrodes. It was concluded that the newly designed electrode is stable enough to detect the expected signal and, at the same time, has great advantage of easy handling. Less