Fig. 3

Absolute values of the full-loop (lowermost, blue), leakage (middle, red) and total (uppermost, black) magnetic fields at a point of observation located at 5 km east of a south-north railway as functions of time produced by a train travelling from south to north. The leakage current density is assumed to be constant. The maximum allowable noise level at a geomagnetic observatory (10 pT) is shown by the horizontal (light blue) line. The small (black) circles and the small (red) crosses are related to the schedule of the train. Additional details of the calculation are given in the text.