Abstract
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.
Highlights
Geomagnetic field variations induce geoelectric fields in the Earth and in man-made conductors at the Earth’s surface such as power systems, pipelines, phone cables and railway circuits, e.g. [1]
An Fast Fourier Transform (FFT) of the geomagnetic field variation gives the magnetic field spectrum, and each spectral component is multiplied by the corresponding complex value of the Earth transfer function to give the geoelectric field spectrum
An inverse FFT of the geoelectric field spectrum gives the geoelectric field in the time domain [28]
Summary
Geomagnetic field variations induce geoelectric fields in the Earth and in man-made conductors at the Earth’s surface such as power systems, pipelines, phone cables and railway circuits, e.g. [1]. First we explain the process of geomagnetic induction in the Earth and derive the equations relating the geoelectric and geomagnetic fields at the Earth’s surface These are used to calculate the Earth transfer functions for two models: a) an Earth with uniform conductivity, and b) an Earth represented by multiple layers with different conductivities to represent the change in Earth conductivity with depth. We create a dataset of a synthetic geomagnetic field variation and use this with the two Earth model transfer functions to produce an exact analytic solution for the geoelectric field in each case. Utilizing the definition (6) of the transfer function K (f ), equations (11) and (12) give
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