Analytic Geomagnetic and Geoelectric Fields

Geomagnetic field variations produce geoelectric fields that can affect the operation of technological networks at the Earth’s surface, including power systems, pipelines, phone cables and railway circuits. To assess the geomagnetic hazard to this technology, it is necessary to model the geomagnetically induced currents (GIC) produced in these systems during geomagnetic disturbances. This requires use of geomagnetic data with appropriate Earth conductivity models to calculate the geoelectric fields that drive GIC. To provide a way of testing geoelectric field calculation software, we provide a benchmark test case by defining a synthetic geomagnetic field variation and deriving exact analytic expressions for the Earth response based on both uniform and layered Earth conductivity models. These are then used to provide exact analytic expressions for the geoelectric fields that would be produced by the synthetic geomagnetic field variation.  The synthetic geomagnetic data can be used as input to numerical geoelectric field calculation software, the output of which can be tested by comparison with the analytically-generated geoelectric fields.