Abstract
Electric fields induced in the conducting Earth by geomagnetic disturbances drive currents in power transmission grids, telecommunication lines or buried pipelines, which can cause service disruptions. A key step in the prediction of the hazard to technological systems during magnetic storms is the calculation of the geoelectric field. To address this issue for mid-latitude regions, we revisit a method that involves 3-D modelling of induction processes in a heterogeneous Earth and the construction of a magnetospheric source model described by low-degree spherical harmonics from observatory magnetic data. The actual electric field, however, is known to be perturbed by galvanic effects, arising from very local near-surface heterogeneities or topography, which cannot be included in the model. Galvanic effects are commonly accounted for with a real-valued time-independent distortion matrix, which linearly relates measured and modelled electric fields. Using data of six magnetic storms that occurred between 2000 and 2003, we estimate distortion matrices for observatory sites onshore and on the ocean bottom. Reliable estimates are obtained, and the modellings are found to explain up to 90% of the measurements. We further find that 3-D modelling is crucial for a correct separation of galvanic and inductive effects and a precise prediction of the shape of electric field time series during magnetic storms. Since the method relies on precomputed responses of a 3-D Earth to geomagnetic disturbances, which can be recycled for each storm, the required computational resources are negligible. Our approach is thus suitable for real-time prediction of geomagnetically induced currents by combining it with reliable forecasts of the source field.
Highlights
Electric fields induced in the conducting Earth by geomagnetic disturbances drive currents in power transmission grids, telecommunication lines or buried pipelines
Geomagnetic and geoelectric fields are in magnetic quiet times dominated by the daily solar quiet (Sq) variations, which cannot fully be described by our chosen set of coefficients (e.g. Schmucker 2013)
In this study, we revisited the method of Püthe and Kuvshinov (2013) to calculate the electric field generated in mid-latitude regions during magnetic storms
Summary
Electric fields induced in the conducting Earth by geomagnetic disturbances drive currents in power transmission grids, telecommunication lines or buried pipelines. These currents, known as geomagnetically induced currents (GIC), are known to cause service disruptions (e.g. Daglis 2004, and references therein). Pulkkinen et al 2012; Viljanen and Pirjola 1994) Both observations and models show that massive GIC caused by intensifications of the. The authors used precomputed electromagnetic (EM) responses of the 3-D model and magnetic data from the global network of geomagnetic observatories to construct the magnetospheric source, described by spherical harmonic expansion (SHE) coefficients. A convolution of the source with the precomputed model responses yielded time series of electric and magnetic fields anywhere on the surface of the Earth
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