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1. A Comparison of FDTD-Predicted Surface Magnetic Fields with SuperMAG, INTERMAGNET, and BATS-R-US and RIM Virtual Magnetometers during a Geomagnetic Storm

   Zhang, Yisong; Simpson, Jamesina J.; Ridley, Aaron; Welling, Dan; Liemohn, Michael (January 2020, Proc. American Geophysical Union Fall Meeting)

   null (Ed.)

   The historical record indicates the possibility of intense coronal mass ejections (CMEs). Energized particles and magnetic fields ejected by coronal mass ejections (CMEs) towards the Earth may disrupt the Earth’s magnetosphere and generate a geomagnetic storm. During a geomagnetic storm, the induced geoelectric field can drive geomagnetically-induced currents (GICs) that flow through ground-based conductors. These GICs have the potential to damage high voltage power transmission systems and cause blackouts. As part of the NSF-funded Comprehensive Hazard Analysis for Resilience to Geomagnetic Extreme Disturbances (CHARGED) project, a solar-wind-to-lithosphere numerical model of the geoelectric field is being developed. The purpose of this new tool is to drive a new generation of GIC forecasting. As a part of that work, Maxwell’s equations, finite-difference time-domain (FDTD) models of the last stage of the Sun-to-Earth propagation path is being coupled to output generated by the Block Adaptive Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) magnetohydrodynamics model and the Ridley Ionosphere Model (RIM) of ionospheric dynamics. Specifically, three-dimensional (3-D) BATS-R-US and RIM-predicted ionospheric currents occurring in the lower ionosphere during and around the time of the March 17, 2015 storm are modeled in 3-D FDTD models of North America. These models start at a depth of 150 km, and they account for ionospheric currents occurring up to an altitude of 115 km. The resolution of the FDTD models is 22 km (East-West) x 11 km (North-South) x 5 km (radially), and they account for 3-D lithosphere conductivities provided by the U.S. Geological Survey. The FDTD-calculated results are compared with surface magnetic fields measured in the region by SuperMAG and INTERMAGNET magnetometers. The FDTD results are also compared with virtual magnetometer data, which calculates the perturbation of the surface magnetic field using output from the BATS-R-US magnetohydrodynamics model. Comparison plots and an analysis of the results will be provided. 

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2. On the Regional Variability of d B /d t and Its Significance to GIC

   https://doi.org/10.1029/2020SW002497  

   Dimmock, A. P.; Rosenqvist, L.; Welling, D. T.; Viljanen, A.; Honkonen, I.; Boynton, R. J.; Yordanova, E. (July 2020, Space Weather)

   Abstract Faraday's law of induction is responsible for setting up a geoelectric field due to the variations in the geomagnetic field caused by ionospheric currents. This drives geomagnetically induced currents (GICs) which flow in large ground‐based technological infrastructure such as high‐voltage power lines. The geoelectric field is often a localized phenomenon exhibiting significant variations over spatial scales of only hundreds of kilometers. This is due to the complex spatiotemporal behavior of electrical currents flowing in the ionosphere and/or large gradients in the ground conductivity due to highly structured local geological properties. Over some regions, and during large storms, both of these effects become significant. In this study, we quantify the regional variability ofdB/dtusing closely placed IMAGE stations in northern Fennoscandia. The dependency between regional variability, solar wind conditions, and geomagnetic indices are also investigated. Finally, we assess the significance of spatial geomagnetic variations to modeling GICs across a transmission line. Key results from this study are as follows: (1) Regional geomagnetic disturbances are important in modeling GIC during strong storms; (2)dB/dtcan vary by several times up to a factor of three compared to the spatial average; (3)dB/dtand its regional variation is coupled to the energy deposited into the magnetosphere; and (4) regional variability can be more accurately captured and predicted from a local index as opposed to a global one. These results demonstrate the need for denser magnetometer networks at high latitudes where transmission lines extending hundreds of kilometers are present. 

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3. 3D Modeling of Geomagnetically Induced Currents in Sweden—Validation and Extreme Event Analysis

   https://doi.org/10.1029/2021SW002988  

   Rosenqvist, L.; Fristedt, T.; Dimmock, A. P.; Davidsson, P.; Fridström, R.; Hall, J. O.; Hesslow, L.; Kjäll, J.; Smirnov, M. Yu; Welling, D.; et al (March 2022, Space Weather)

   Abstract Rosenqvist and Hall (2019),https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018SW002084developed a proof‐of‐concept modeling capability that incorporates a detailed 3D structure of Earth's electrical conductivity in a geomagnetically induced current estimation procedure (GIC‐SMAP). The model was verified based on GIC measurements in northern Sweden. The study showed that southern Sweden is exposed to stronger electric fields due to a combined effect of low crustal conductivity and the influence of the surrounding coast. This study aims at further verifying the model in this region. GIC measurements on a power line at the west coast of southern Sweden are utilized. The location of the transmission line was selected to include coast effects at the ocean‐land interface to investigate the importance of using 3D induction modeling methods. The model is used to quantify the hazard of severe GICs in this particular transmission line by using historic recordings of strong geomagnetic disturbances. To quantify a worst‐case scenario GICs are calculated from modeled magnetic disturbances by the Space Weather Modeling Framework based on estimates for an idealized extreme interplanetary coronal mass ejection. The observed and estimated GIC based on the 3D GIC‐SMAP procedure in the transmission line in southern Sweden are in good agreement. In contrast, 1D methods underestimate GICs by about 50%. The estimated GICs in the studied transmission line exceed 100 A for one of 14 historical geomagnetic storm intervals. The peak GIC during the sudden impulse phase of a “perfect” storm exceeds 300 A but depends on the locality of the station as the interplanetary magnetic cloud hits Earth. 

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4. On the Relationship Between Geomagnetically Induced Currents and Geomagnetic Field Variations—Illustrated With Case Studies of Pipeline and Power Systems in Regions With Different Conductivity Structures

   https://doi.org/10.1029/2025SW004852  

   Chakraborty, S; Boteler, D H (July 2026, Space Weather)

   Abstract During space weather events, geomagnetic field variations produce geoelectric fields (GEFs) that drive geomagnetically induced currents (GIC), which may affect operation of power systems, pipelines, railway signaling, and submarine cables. It is often assumed that GEFs and GICs are proportional to the rate of change of the magnetic field,∂B/∂t. However, the GEFs drive electric currents in the Earth that themselves create magnetic fields and this complicates the relationship between the GEFs (and associated GICs) and geomagnetic field variations. Previous theoretical studies have shown this can lead to GEFs that are correlated with eitherB(t)or∂B/∂tdepending on the Earth conductivity structure. In this paper we extend this work to determine the electric field/magnetic field relationships for two limiting cases of the conductivity structure; and use these to calculate the GIC produced in a pipeline and a power system. The results show that GICs follow the variations inB(t)when the system is in a region with a conductive surface layer on top of a resistive substratum; but follow∂B/∂twhen the system is in a region with a resistive surface layer on top of conductive substratum. This illustrates the range of responses that can be obtained with different Earth conductivity structures and shows the importance of including Earth conductivity models in the calculations of GIC. It also shows that neitherB(t)nor∂B/∂trepresents a reliable proxy for GIC and that a better proxy is consistent with empirical proxy proposed by Marshall et al. (2010),https://doi.org/10.1029/2009sw000553. 

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5. Modeling the Geomagnetic Response to the September 2017 Space Weather Event Over Fennoscandia Using the Space Weather Modeling Framework: Studying the Impacts of Spatial Resolution

   https://doi.org/10.1029/2020SW002683  

   Dimmock, A. P.; Welling, D. T.; Rosenqvist, L.; Forsyth, C.; Freeman, M. P.; Rae, I. J.; Viljanen, A.; Vandegriff, E.; Boynton, R. J.; Balikhin, M. A.; et al (May 2021, Space Weather)

   Abstract We must be able to predict and mitigate against geomagnetically induced current (GIC) effects to minimize socio‐economic impacts. This study employs the space weather modeling framework (SWMF) to model the geomagnetic response over Fennoscandia to the September 7–8, 2017 event. Of key importance to this study is the effects of spatial resolution in terms of regional forecasts and improved GIC modeling results. Therefore, we ran the model at comparatively low, medium, and high spatial resolutions. The virtual magnetometers from each model run are compared with observations from the IMAGE magnetometer network across various latitudes and over regional‐scales. The virtual magnetometer data from the SWMF are coupled with a local ground conductivity model which is used to calculate the geoelectric field and estimate GICs in a Finnish natural gas pipeline. This investigation has lead to several important results in which higher resolution yielded: (1) more realistic amplitudes and timings of GICs, (2) higher amplitude geomagnetic disturbances across latitudes, and (3) increased regional variations in terms of differences between stations. Despite this, substorms remain a significant challenge to surface magnetic field prediction from global magnetohydrodynamic modeling. For example, in the presence of multiple large substorms, the associated large‐amplitude depressions were not captured, which caused the largest model‐data deviations. The results from this work are of key importance to both modelers and space weather operators. Particularly when the goal is to obtain improved regional forecasts of geomagnetic disturbances and/or more realistic estimates of the geoelectric field. 

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