Comparison of Geoelectric Fields Computed by the Complex Image, Magnetotelluric, and Finite-Difference Time-Domain Methods

It is important to be able to accurately predict geoelectric field behavior so that potential space weather hazards to large grounded infrastructure, such as electric power grids, smart grids, oil and gas pipelines, and railway systems, can be better understood. This study presents a comparison of geoelectric fields predicted via the complex image method (CIM), the magnetotelluric (MT) impedance method, and Maxwell's equations finite-difference time-domain (FDTD) method. The CIM and MT methods have already been widely applied to the prediction of geoelectric fields, however, there are only a small number of FDTD-related papers in this area. The FDTD method is of interest because it can accommodate more complex and realistic ground and source geometries than the other methods. For simplicity, the comparison of the three methods in this paper involves one-dimensional ground conductivity profiles along with either a sheet or an infinitely long line source current in the ionosphere. The FDTD method is found to accurately reproduce the results obtained by the MT method for a planar (sheet current) source. Additionally, for a non-planar (line) source geometry, the FDTD-calculated geoelectric fields agree with those predicted by the CIM, but not the MT method. In other words, the FDTD method accurately predicts geoelectric fields for both types of scenarios, whereas the MT method can only accommodate planar ionospheric source fields. The paper concludes with a discussion of the overall strengths and limitations of each method.