Fig. 5

Absolute value of the (total) magnetic field a point of observation located at 5 km east of a south-north railway as a function of time produced by two identical trains travelling from south to north at 90-s separation. The thicker lower (black) and the thinner upper (blue) curves correspond to a constant and a linearly changing leakage current density, respectively. 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 first train. Additional details of the calculations are given in the text.