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.
On the man-made contamination on ULF measurements: evidence for disturbances related to an electrified DC railway
Abstract. An analysis of measurements performed at L'Aquila (Italy) during a deep minimum of solar and magnetospheric activity (2008–2010) allowed for the evaluation of possible contamination of the ultralow-frequency (ULF) spectrum (f a 1–500 mHz) from artificial disturbances, practically in absence of natural signals. In addition, the city evacuation and the interruption of all industrial and social activities after the strong earthquake of 6 April 2009 allowed also for the examination of possible changes of the contamination level under remarkably changed environmental conditions. Our analysis reveals a persistent, season-independent, artificial signal, with the same characteristics in the H and Z components, that affects during daytime hours the entire spectrum; such contamination persists after the city evacuation. We speculate that the DC electrified railway (located a 33 km from the Geomagnetic Observatory of L'Aquila, it maintained the same train traffic after the earthquake) is responsible for the observed disturbances.
Global Hydromagnetic Wave Ducts in the Exosphere
IN 1957, one of us (H.A.B.) considered the initiation of an earth-magnetic field experiment to detect hydromagnetic waves in the upper ionosphere and exosphere. He suggested the use of very large wire loops (of about 100 km.2 area) as pick-up systems for earth-magnetic field perturbations. A large loop has the advantage of a very high signal-to-noise ratio, since it effectively averages out local magnetic interference.