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TELLURIC CURRENTS: THE NATURAL ENVIRONMENT AND INTERACTIONS WITH MAN-MADE SYSTEMS 245 luric currents in terms of a compressed magnetosphere with magnetopause and magnetosphere currents electromagnetically inducing over a three-layer conducting Earth. Summarizing, shutdowns in both land and sea cables, as well as fires, have been caused by telluric currents induced by geomagnetic storms, and suitable precautions have to be taken (Root, 1979) in order to attempt to avoid them. A singular example of man-made telluric current "pollution" occurred when a high-altitude nuclear bomb test produced perturbations in the Earth's radiation belts and geomagnetic field. As recounted in Axe (1968): The disturbance was just detectable on the power-feeding voltage and current recorder charts on the Australia-New Zealand, United Kingdom-Sweden and Bournemouth-Jersey systems. On a circuit originally set up on the Donaghadee-Port Kail No. 3 cable for the measurement of voltage due to water flow, the disturbance was clearly recorded. The data at the time of the event are shown in Figure 16.10 (Axe, 1968). All the effects considered above refer to electromagnetic induction from ionospheric and magnetospheric variations. However, there are also effects on submarine communication cables related to water flows (tidal and otherwise). The problem has been extensively reviewed by Meloni et al. (1983); see later section. Less dramatic, although relevant, man-induced telluric current perturbations on land cables should be expected in heavily industrialized or populated areas (e.g., Kovalevskiy et al., 1961). Powerlines The historical record of powerlines being greatly distributed or completely disrupted by geomagnetic storms appears somewhat less detailed than that for communications cables. One interruption of service occurred on March 24, 1940, in New England, New York, eastern Pennsylvania, Minnesota, Quebec, and Ontario (Davidson, 1940; Brooks, 1959). As well, during the great geomagnetic storm of February 11, 1958, the Toronto area suffered from a blackout produced by a geomagnetic storm. Currents up to about 100 A were induced in some northern latitude transformers during the great storm of August 4, 1972 (McKinnon, 1972). Induced currents on power systems in the auroral zone have been discussed by Aspnes et al. (1981) and Akasofu and Aspnes (1982; see Figure 16.11). Some of the most detailed investigations aimed at establishing engineering relations for power systems have been carried out by Figure 16.10 Effect of the Starfish explosion measured on the center-conductor voltage of the Donaghadee-Kail (Irish Sea) number 3 cable. From Axe (1968). Figure 16.11 Simultaneous recordings of geomagnetic induction effects observed as current surges in a positive relay system and an auto transformer in a power substation near Fairbanks, Alaska, on December 19, 1980 (from Akasofu and Aspnes, 1982).