The Earth's Electrical Environment (1986) / Chapter Skim
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Pages 234-240
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From page 234... ...
to evaluate, on a global scale, possible currents between ground and air suffered large uncertainties from the approximations used. As noted briefly in the Introduction, the cause of telluric currents is either electromagnetic induction by the time-varying geomagnetic field produced by the ionosphere and/or magnetosphere or by water movement across the permanent
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From page 235... ...
The North German anomaly, with a depth-integrated conductivity ~ 3000 mhos, is equivalent to-750 m of seawater. Another physical factor affecting conductivity, and thus telluric currents, is temperature.
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From page 236... ...
Analogously, a different function relates the continental heat flow to age.) Three additional aspects of the conductivity structure of the Earth affect the flow of telluric currents spatial gradients, temporal variations, and channeling.
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From page 237... ...
The central solid line represents the skin depth estimate for the actual Earth, assuming a planar half-space of uniform conductivity equal to the conductivity of the lowest evaluated depth of penetration; the upper and lower solid lines are explained below. The central line represents a lower limit on the depth.
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From page 238... ...
238 10 r ~too ~ / _ / o ~ i ~ ( OoW°~ , ~/~/: ,, o , ,, ,, Ace, _-Jo , ~ \ ((// of into/ ~°° - \J ~ _.
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From page 239... ...
239 ,3 it\ ~ ~ - ~ Vat 1 / ._ ~ ~1 1 ,~ jp~.
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From page 240... ...
The issue revolves around the interpretation of the measured telluric currents. Should the measurements at some given site be interpreted in terms of electromagnetic induction on a local (or in any case on a small-scale)
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