The Alaskan oil pipeline is a 1.28 x 103-km long, grounded conductor extending from Prudhoe Bay on the Arctic Ocean to Valdez on the Gulf of Alaska. The pipe has a mean diameter of 1.22 m, an average wall thickness of 1.30 cm, and a steel conductivity of about 4.2 x 106 mhos/m. The end-to-end resistance of the pipeline is about 6.2 ohms and the resistance per unit length of pipe is about 4.82 x 10-6 ohms/m. The route of this pipeline extends from about 61° to 69° geomagnetic latitude (Figure 1) beneath the active region of an ionospheric electrojet current in the northern auroral zone. It is well known that the time-varying currents of this electrojet flow in established patterns that favor the geomagnetic westward direction at the latitudes of northern Alaska during the midnight hours. Such currents occur in close association with optical auroras as a part of the enhanced solar-terrestrial disturbance phenomena. The magnetic fields of these strong ionospheric currents cause large decreases in the geomagnetic northward component of the magnetic field, H, observed at the Earth's surface. The field vectors of rapid geomagnetic field fluctuations, at times of the occurrence of the electrojet, usually display highly eccentric ellipses with their major axes perpendicular to the jet current direction (ref.6). Figure 2 illustrates how the north-south geomagnetic field fluctuation amplitudes vary as a function of geomagnetic latitude and activity level. The ends and central location of the pipeline, indicated by arrowheads in that figure, are seen to be in regions of large-amplitude field changes.
