The Jacobian of the non-linear mapping from model parameters to observations is a key component in all gradient-based inversion methods, including variants on Gauss-Newton and conjugate gradients. Here, we develop general mathematical framework for computations arising electromagnetic (EM) geophysical inverse problems. Our analysis, which based discrete formulation forward problem, divides into components (data functionals, adjoint solvers, parameter mappings), clarifies dependencies among...

We develop a non-linear conjugate gradient inversion for global long period electromagnetic induction studies. The scheme requires computation of derivatives the regularized penalty functional. derive analytical and numerical expressions these derivatives, associated Jacobian, show how can be efficiently implemented by generalizing extending an existing finite difference forward solver. Using layered spherical harmonics to parametrize model space, we invert range synthetic data sets test...

Research Article| May 01, 2012 Crust and upper mantle electrical conductivity beneath the Yellowstone Hotspot Track A. Kelbert; Kelbert 1College of Earth, Ocean Atmospheric Sciences, Oregon State University, 104 CEOAS Admin Building, Corvallis, 97331, USA Search for other works by this author on: GSW Google Scholar G. D. Egbert; Egbert C. deGroot-Hedlin 2Scripps Institution Oceanography, University California−San Diego, La Jolla, California 92037, Author Article Information Publisher:...

Abstract Geoelectric fields at the Earth's surface caused by magnetic storms constitute a hazard to operation of electric power grids and related infrastructure. The ability estimate these geoelectric in close real time provide local predictions would better equip industry mitigate negative impacts on their operations. Here we report progress toward this goal: development robust algorithms that convolve storm series with frequency domain impedance for realistic three‐dimensional (3‐D) Earth,...

Abstract Geomagnetic disturbances cause perturbations in the Earth’s magnetic field which, by principle of electromagnetic induction, turn electric currents to flow Earth. These geomagnetically induced (GICs) also enter man-made technological conductors that are grounded; notably, telegraph systems, submarine cables and pipelines, and, perhaps most significantly, power grids, where transformer groundings at grid substations serve as entry points for GICs. The strength GICs through a depends...

Abstract Maps of extreme value geoelectric field amplitude are constructed for the Mid‐Atlantic United States, a region with high population density and critically important power grid infrastructure. Geoelectric time series years 1983–2014 estimated by convolving Earth surface impedances obtained from 61 magnetotelluric survey sites across historical 1 min (2 Nyquist) measurements geomagnetic variation nearby observatory. Statistical models fitted to maximum amplitudes occurring during...

Abstract Commonly, one‐dimensional (1‐D) Earth impedances have been used to calculate the voltages induced across electric power transmission lines during geomagnetic storms under assumption that much of three‐dimensional structure gets smoothed when integrating along lines. We voltage in mid‐Atlantic region with both regional 1‐D and 64 empirical 3‐D obtained from a magnetotelluric survey. The use produces substantially more spatial variance calculated voltages, being than an order...

Abstract Intense geoelectric fields during geomagnetic storms generate geomagnetically induced currents in power grids and other infrastructure, necessitating an understanding of their causes, for example, through coordinated space ground observations. This study investigates localized intense ( E ) B field perturbations following Interplanetary Magnetic Field (IMF) turning a storm on 25 October 2011. Observations from EarthScope magnetotelluric sites the upper Midwest United States revealed...

In its 18-year lifetime, the United States Magnetotelluric Array (USMTArray) has acquired more than 1,700 long-period magnetotelluric (MT) stations covering entirety of contiguous States. Funding from multiple federal agencies sustained this effort to completion in 2024. Important components project included active guidance and participation scientific community, open timely availability all data, application consistent instrumentation robust data processing. Together with parallel...

The Science Explorer (SciX) digital library is a cutting-edge solution designed to address the growing complexity of accessing, evaluating, and synthesizing expanding body literature in Earth environmental sciences. While System itself remains as intricate ever, challenge today lies navigating an increasingly vast diverse array research data. SciX responds this need by providing centralized, open-access platform that enhances discovery integration scientific literature, all while adhering...

Abstract Long‐period global‐scale electromagnetic induction studies of deep Earth conductivity are based almost exclusively on magnetovariational methods and require accurate models external source spatial structure. We describe approaches to inverting for both the sources three‐dimensional (3‐D) variations apply these long‐period ( T ≥1.2 days) geomagnetic observatory data. Our scheme involves three steps: (1) Observatory data from 60 years (only partly overlapping with many large gaps)...

Abstract In support of a multiagency project for assessing induction hazards, we present maps extreme‐value geoelectric amplitudes over about half the continental United States. These are constructed using parameterization induction: estimates Earth surface impedance, obtained at discrete geographic sites from magnetotelluric survey data, convolved with latitude‐dependent statistical geomagnetic activity, decades magnetic observatory data. Geoelectric estimated waveforms having 240 s...

Abstract A once‐per‐century geoelectric hazard map is created for the U.S. high‐voltage power grid. statistical extrapolation from 31 years of magnetic field measurements made by identifying 84 geomagnetic storms with Kp and Dst indices. Data 24 observatories, 1,079 magnetotelluric survey sites, 17,258 transmission lines are utilized to perform a analysis most comprehensive data publicly available. With these data, we estimate fields at sites calculate theoretical voltages within in...

Abstract A study is made of the relations between geomagnetic and geoelectric field variation, Earth‐surface impedance, operational interference (“anomalies”) experienced on electric‐power systems across contiguous United States during 13–14 March, 1989, magnetic storm. For this, a 1‐min‐resolution sequence maps constructed from magnetometer time series acquired at ground‐based observatories. Induced are calculated by convolving with magnetotelluric impedance tensors. During storm, anomalies...

A R Y Global electromagnetic (EM) induction studies have been the focus of increasing attention during past few years.A primary stimulus for this interest has increased quality, coverage and variety newly available data sets especially from recent low-Earth-orbiting satellite missions.The combination traditional ground-based with satellite-borne measurements presents intriguing opportunity to attack most challenging problem deep EM studies: recovery 3-D variations electrical conductivity in...

Abstract Maps are presented of extreme‐value geoelectric field amplitude and horizontal polarization for the Northeast United States. These maps derived from time series calculated sites across by frequency‐domain multiplication (time‐domain convolution) 172 magnetotelluric impedance tensors, acquired during a survey, with decades‐long, 1‐min resolution geomagnetic variation, at three magnetic observatories. The show that, intense storms, high hazards realized electrically resistive, igneous...

Abstract Geomagnetically induced currents (GICs) are quasi‐direct current (DC) electric that flow in technological conductors during geomagnetic storms. Extreme GICs hazardous to man‐made infrastructure. enter and exit the systems, such as power grid, at grounding points, their magnitudes depend on underground. They are, therefore, a function of Earth's electrical conductivity, represented ground level Earth impedances, well resistance parameters network. Traditional GIC estimation practices...

Abstract Intense geoelectric fields during geomagnetic storms drive geomagnetically induced currents in power grids and other infrastructure, yet there are limited direct measurements of these storm‐time fields. Moreover, most previous studies examining focused on single events or small geographic regions, making it difficult to determine the typical source(s) intense We perform first comparative analysis (a) sources over multiple storms, (b) using 1‐s cadence field made at (c)...

Abstract Geomagnetically induced currents (GICs) result from the interaction of time variation ground magnetic field during a geomagnetic disturbance with Earth's deep electrical resistivity structure. In this study, we simulate GICs in hypothetical representation low‐latitude power transmission network located mainly over large Paleozoic Paraná basin (PB) southern Brazil. Two intense storms June and December 2015 are chosen geoelectric fields calculated by convolving three‐dimensional (3‐D)...