Large-amplitude ULF electromagnetic fields from BART

Starting in 1972, persistent large-amplitude magnetic signals were observed in recordings of ultra-low-frequency (ULF, frequencies less than 5 Hz) geomagnetic field fluctuations made on the Stanford campus. The energy of these ULF signals is concentrated predominantly at frequencies below about 0.3 Hz and their amplitude, which has increased greatly since 1972, is at least ten times greater than the normal natural background level of geomagnetic activity, i.e., it is comparable to the level observed during great geomagnetic storms. ULF magnetic field measurements at additional locations away from the Stanford campus have enabled us to identify the San Francisco Bay Area Rapid Transit (BART) system as the source of these large-amplitude magnetic fields, which appear to be produced throughout the entire Bay area and vicinity (area ≈100 km2). Primary power for the BART trains is provided by a 1000 V dc third rail (total length ≈270 km) and a single loaded 10-car train can draw as much as 7 Mw during acceleration. Large fluctuating currents (5 to 10 kA) therefore flow in the third rail and associated conductors, with the result that the entire BART system constitutes a large ULF “antenna.” Similar systems planned or already in operation in other parts of the US (e.g., the Washington, DC, Metro) will probably also produce similar large-amplitude ULF electromagnetic fields.

[1]  N. G. Hingorani,et al.  Power: HVDC for the long run: High-voltage de transmission may be a viable alternative to ac transmission for long-distance routes , 1976, IEEE Spectrum.

[2]  Gordon D. Friedlander.  The BART chronicle , 1972, IEEE Spectrum.

[3]  K. Harker.  Generation of ULF waves by electric or magnetic dipoles. [propagation from earth surface to ionosphere] , 1975 .

[4]  A. Fraser-Smith,et al.  The effect of the conducting earth on the micropulsation‐generating capability of a ground‐based current loop , 1974 .

[5]  T. Bell.  ULF wave generation through particle precipitation induced by VLF transmitters , 1976 .

[6]  Gordon D. Friedlander.  More BART hardware , 1972, IEEE Spectrum.

[7]  Gordon D. Friedlander.  BART's hardware - from bolts to computers , 1972, IEEE Spectrum.

[8]  J. R. Storey,et al.  Controlled artificial generation of geomagnetic pulsations , 1975, Nature.

[9]  R. W. Ellison,et al.  RF Noise Radiated by a Rapid Transit System - Addendum , 1974 .

[10]  C.W. Condit,et al.  Railroad electrification in the United States , 1976, Proceedings of the IEEE.

[11]  A. Fraser-Smith,et al.  Generation of Alfven waves in the magnetosphere by parametric interaction between whistlers , 1974 .

[12]  C. Greifinger,et al.  Generation of ULF by a horizontal electric dipole , 1974 .

[13]  A. Fraser-Smith,et al.  Initial observations of the artificial stimulation of ULF pulsations by pulsed VLF transmissions , 1975 .

[14]  J. Davis,et al.  A Quest for a Controllable ULF Wave Source , 1974, IEEE Trans. Commun..

[15]  C. Greifinger.  Feasibility of ground‐based generation of artificial micropulsations , 1972 .