Effect of Terrestrial Electromagnetic Storms on Wireline Communications

Effects of natural electromagnetic phenomena on wireline circuits are discussed. An important factor causing degradation of system operation or damage to equipment is the occurrence of earth currents, or geoelectric variations, associated with electromagnetic storms. Three to six earth-current storms occur yearly, during and after the maximum of the sunspot cycle. Peak disturbances last 10 to 30 minutes and return to normal within 6 to 48 hours. Typical disturbances are 3 to 20 v/km in the auroral zones, 0.5 to 5.0 v/km in middle latitudes, and less than 100 mv/km near the equator. Current flow is generally N-S, except near the geomagnetic equator where it is E-W. Undisturbed diurnal variations exhibit the same general characteristics, but attain values in the range of 5 to 300 mv/km. Cases are cited of adverse effects on commercial circuits; open wire, buried cable, and submarine cable systems are compared. Geophysical processes underlying geoelectric variations are discussed briefly.