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Abstract Geomagnetically induced currents (GICs) result from the interaction of the time variation of ground magnetic field during a geomagnetic disturbance with the Earth's deep electrical resistivity structure. In this study, we simulate induced GICs in a hypothetical representation of a low‐latitude power transmission network located mainly over the large Paleozoic Paraná basin (PB) in southern Brazil. Two intense geomagnetic storms in June and December 2015 are chosen and geoelectric fields are calculated by convolving a three‐dimensional (3‐D) Earth resistivity model with recorded geomagnetic variations. ThedB/dtproxy often used to characterize GIC activity fails during the June storm mainly due to the relationship of the instantaneous geoelectric field to previous magnetic field values. Precise resistances of network components are unknown, so assumptions are made for calculating GIC flows from the derived geoelectric field. The largest GICs are modeled in regions of low conductance in the 3‐D resistivity model, concentrated in an isolated substation at the northern edge of the network and in a cluster of substations in its central part where the east‐west (E‐W) oriented transmission lines coincide with the orientation of the instantaneous geoelectric field. The maximum magnitude of the modeled GIC was obtained during the main phase of the June storm, modeled at a northern substation, while the lowest magnitudes were found over prominent crustal anomalies along the PB axis and bordering the continental margin. The simulation results will be used to prospect the optimal substations for installation of GIC monitoring equipment. 

For the past 18-years Oregon State University and its contractors - under the support of NSF (2006-2018), NASA (2019-2020) and USGS (2020-2024)- installed temporary (weeks-to-months; at 7 Backbone stations - years) long-period MT stations that measure ground-level vector electric and magnetic fields on a 70-km grid of points spanning the conterminous US. A total of 1711 transportable stations whose data meet data quality control standards will have been installed, operated and extracted by mid-2024, completing the MTArray in CONUS. We generate MT Impedance tensors (“EMTF”s, induction vectors and related quantities from the MT time series, suitable for determining the 3-D electrical structure of the crust and upper mantle. The impedances, induction vectors, and/or derived 3-D electrical models can be used to estimate ground-level electric fields from measurements or models of ground-level magnetic fields. These can be integrated along the paths of power grid transmission lines and flowed through power grid equivalent electrical circuits to determine GIC intensity, transformer heat and vibration, and reactive power loss. A look to the future: With a sufficiently dense, real-time telemetering network of MT stations, we have demonstrated how a convolutional neural network trained on measured time series from an array of MT stations may be used to forecast ground-level fields more than 30-minutes in the future, and the potential this has for alerting power utilities of incoming risks to specific HV transformers on the transmission network (reported at this workshop in 2022). 

Ground-based magnetometers used to measure magnetic fields on the Earth’s surface (B) have played a central role in the development of Heliophysics research for more than a century. These versatile instruments have been adapted to study everything from polar cap dynamics to the equatorial electrojet, from solar wind-magnetosphere-ionosphere coupling to real-time monitoring of space weather impacts on power grids. Due to their low costs and relatively straightforward operational procedures, these instruments have been deployed in large numbers in support of Heliophysics education and citizen science activities. They are also widely used in Heliophysics research internationally and more broadly in the geosciences, lending themselves to international and interdisciplinary collaborations; for example, ground-based electrometers collocated with magnetometers provide important information on the inductive coupling of external magnetic fields to the Earth’s interior through the induced electric field (E). The purpose of this white paper is to (1) summarize present ground-based magnetometer infrastructure, with a focus on US-based activities, (2) summarize research that is needed to improve our understanding of the causes and consequences of B variations, (3) describe the infrastructure and policies needed to support this research and improve space weather models and nowcasts/forecasts. We emphasize a strategic shift to proactively identify operational efficiencies and engage all stakeholders who need B and E to work together to intelligently design new coverage and instrumentation requirements. 

For the past sixteen years under the support of NSF, NASA and most recently the US Geological Survey, we have been systematically measuring electric and magnetic field time series from moving arrays of magnetotelluric (MT) instrumentation spanning the conterminous US and the interior of Alaska. While originally motivated by questions of the structure and evolution of the North American continent, the resulting 3-D electrical conductivity structure of the Earth's crust and upper mantle and the electromagnetic impedance data derived from this work have in recent years proved of considerable importance to mitigating risk to critical infrastructure (most notably, the power grid) from geomagnetically induced currents caused by space weather and electromagnetic pulse events. Under current NSF support we are exploring how to combine real-time magnetic observatory data streams with this information and with power flow simulations of the power grid to provide real-time alerting information of GIC impacts on high-voltage transformers to electric utilities. In the present work we go beyond real-time and present preliminary results of our efforts to train neural networks to assimilate data from dense arrays of ground-based MT stations in Alaska to provide forecasts of ground electric and magnetic field time series that could in future, with installation of permanent MT arrays, provide actionable intelligence to utilities ahead of GICs impacting their networks. 

Severe geomagnetic storms can generate significant geo-electric fields that drive damaging quasi-direct currents within electric power grids. In "Space Weather Phase 1 Benchmarks," a report published in June 2018 by the Space Weather Operations, Research, and Mitigation (SWORM) Subcommittee on behalf of the National Science and Technology Council (NSTC), the "Induced Geo-electric Fields" working group (WG) summarized their objectives to: (1) assess the feasibility of establishing functional benchmarks for induced geo-electric fields using currently available storm data sets, existing models, and published literature; and (2) use the existing body of work to produce benchmarks for induced geo-electric fields for specific regions of the United States. To address this, they focused on developing a statistical product that captured maps of geo-electric hazard. Recently, our "next steps" WG reviewed these benchmarks to assess whether they are reasonable, aligned with the stated objectives, and up-to-date, based on new analyses as well as input from the community. We also considered whether the methodology used to derive them should be revised. In this presentation, we summarize the main findings of this WG, including recommendations for future data collection and/or studies that would improve their accuracy and usability, whilst at the same time, reducing the uncertainties associated with them. 

By fusing data obtained from finely spaced continental-scale, magnetotelluric (MT) measurements used for geophysical imaging of the electrical conductivity variations of the Earth's crust and mantle, real-time data of the geomagnetic field variations at a sparse network of fixed geomagnetic observatory and variometer stations, power transmission system sensor data such as neutral ground return current, synchrophasor and other sensor data, information on power grid topology and state, and by applying algorithms we have developed to project the real-time stream of magnetic observatory and variometer data through the frequency-dependent tensor impedances derived from the MT data at each temporary station, we calculate the anomalous voltages on power transmission substations induced by geomagnetically induced currents. Our solution accounts for the first-order impacts on the induced voltages that are due to the effects of 3-D variations in ground (Earth's crust and upper mantle) electrical conductivity structure. These effects when convolved with the path integral of the induced vector ground electric field along the transmission lines are the dominant term in determining the intensity of the geomagnetically induced currents in the system; considerably more so than geomagnetic latitude scaling effects. We discuss integration of real-time geophysical estimates of geomagnetic disturbance induced substation voltages with DC and AC power flow simulations on increasingly realistic models of the topology and state of regional power grids. We are integrating our workflow with the open source PowerModelsGMD.jl power flow simulator developed at Los Alamos National Laboratory, and describe simulations of real-time assessments of stress on critical assets of the power grid including reactive power loss, phase deviations, transformer heating and other metrics of transmission system stress. Such efforts to provide a real-time assessment of risk to critical assets can also inform statistical assessments of system vulnerabilities to "100-yr" or "Carrington" level geomagnetic disturbances. We will discuss how such efforts are informing the development of updated standards that may impact the future regulatory environment that governs efforts to maintain a resilient power transmission system.