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TitleThe magnetic and electric fields produced in the sea during geomagnetic disturbances
AuthorBoteler, D H; Pirjola, R J
SourcePure and Applied Geophysics vol. 160, 2003 p. 1695-1716,
Alt SeriesEarth Sciences Sector, Contribution Series 20100344
Mediapaper; on-line; digital
File formatpdf
Subjectsgeophysics; extraterrestrial geology; geomagnetism; geomagnetic fields; geomagnetic variations; pipelines; electromagnetic induction
ProgramTargeted Hazard Assessments in Northern Canada, Public Safety Geoscience
AbstractTo understand geomagnetic effects on systems with long conductors it is necessary to know the electric field those systems experience. For surface conductors such as power systems and pipelines this can easily be calculated from the magnetic field variations at the surface using the surface impedance of the earth. However, for calculating the electric fields in pipelines and submarine cables at the seafloor it is necessary to take account of the attenuating effect of the conducting seawater. Assuming that the fields are vertically propagating plane waves, we derive the transfer functions between the electric and magnetic fields at the seafloor and the magnetic field variations at the sea surface. These transfer functions are then used, with surface magnetic field data, to determine the power spectra of the seafloor magnetic and electric fields in a shallow sea (depth 100 m) and in the deep ocean (depth 5 km) for different values of the Kp magnetic activity index. For the period range considered (2 min to 3 hrs) the spectral characteristics of the seafloor magnetic and electric fields for a 100 m deep sea are very similar to those of the surface fields. For the deep ocean the seafloor spectra show a faster decrease in spectral density with increasing frequency compared to the surface fields. The results obtained are shown to be consistent with seafloor observations. Assessment of the seafloor electric fields produced by different levels of geomagnetic activity can be useful in the design of the power feed equipment for submarine cables and cathodic protection for undersea pipelines.