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.
Calculation of Magnetic Field Disturbance Produced by Electric Railway
Magnetic field disturbance by leakage current of electric railways is a serious problem for magnetic observations. We can get an exact solution in various situations of the route of railway, distributions of power substations and electric railcars by the method developed herein. The developed method yields a smaller estimating magnetic field disturbance compared with the old method.
Analysis of geomagnetic micropulsations due to high-altitude nuclear explosions
Spectrums of the magnetic disturbances from the high-altitude nuclear explosion of July 9, 1962, computed from flux-rate variograph recordings obtained at Huancayo, Peru; Uppsala, Sweden; Reykjavik, Iceland; and Resolute Bay, Canada; are compared with those computed for several natural sudden commencements. The sudden commencement data show a lack of distinct spectral peaks compared with the spectrums of the nuclear explosion. The Alfven velocity-altitude profile indicates that MHD waves can be trapped in a waveguide in the altitude range from 300 to 3000 km, thus producing resonant oscillations in the waveguide. The line nature of the explosion spectrums suggests that a resonance mechanism is appropriate. A review of the theory for a simple MHD resonance model is presented, and computed eigenfrequencies are compared with the observed data. The observed data are in fair agreement with theoretical predictions. An interesting feature of the present study is the evaluation of the dimensionless dissipation parameter Q, which is of the order of 1 to 10 for MHD waves, suggesting that simplifying assumptions neglecting energy dissipation mechanisms must be dropped.