DC railways and the magnetic fields they produce—the geomagnetic context
DC electric railways produce magnetic fields, not only from the intended traction currents, but also from unintended earth-leakage currents; these fields, particularly those from the leakage currents, are becoming an increasing problem for geomagneticians. This paper introduces the relevant properties of DC-railway traction-power circuits, and the various ways in which earth-leakage currents are produced, and discusses models of how these leakage currents vary along the track and with train position. It describes the geometry of the resultant magnetic fields, and gives the formal algebra for calculating the magnetic field when these leakage currents are known, but also suggests some simple approximations that could be used when the current distribution is not known in detail. This paper also summarises previous relevant papers.
MAN-MADE TELLURIC MICROPULSATIONS
Man-made telluric micropulsations in the frequency range 0.001 2 Hz to 0.12 Hz have been investigated near Montreal, Canada. Distinct telluric signals caused by electric-train activity have been identified and compared with the associated magnetic effects. The results indicate that some electromagnetic disturbances of this kind may be more easily detected and identified by telluric means than by magnetic means.
Feasibility of ground‐based generation of artificial micropulsations
The magnetic field generated by a ground-based horizontal frame antenna operating in the Pc 1 frequency range is calculated for different ionospheric conditions. The generated signal can propagate laterally in the ionospheric waveguide and, as a result of mode conversion in the lower ionosphere, upward into the magnetosphere along the field lines above the source. For (nighttime) waveguide propagation, generation of fields of the order of 10 mγ at distances of thousands of kilometers requires the magnetic moment of an antenna of the order of 100 km in radius carrying a current of the order of 1 ka. A magnetic moment of the same order will produce upward-going fields of the order of tens of milligammas at the top of the ionosphere, for either daytime or nighttime conditions. Generation of micropulsations by a ground-based rotating superconducting magnet is briefly considered and is found to be well outside the range of current feasibility.