Article
Geochemistry & Geophysics
Nils Olsen
Summary: The sensitivity of magnetic measurements taken by satellites in elliptical orbits to the lithospheric magnetic field is studied. The variances of the lithospheric Gauss coefficients for different satellite orbital constellations are compared and analytical expressions for the variances are presented. It is found that low-altitude magnetic data collected by satellites in low-perigee elliptical orbits enable improved global lithospheric field modelling at spatial wavelengths beyond what is currently possible with data from satellites in circular orbits.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
Wolfgang Szwillus, Eldar Baykiev, Yixiati Dilixiati, Joerg Ebbing
Summary: Estimating the depth to magnetic bottom (DTB) is a challenging problem in potential field inversion. Spectral methods, the most popular approach, have been questioned for their reliability. This study proposes a Bayesian approach to estimate susceptibility and DTB from magnetic data using a two-step inversion procedure. The uncertainties due to unknown hyperparameters are rigorously propagated, and pointwise constraints based on heat flow measurements can be easily included. Synthetic tests and application to real data demonstrate the accuracy and applicability of the new algorithm.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
M. Istas, N. Gillet, C. C. Finlay, M. D. Hammer, L. Huder
Summary: In this study, the pygeodyn data assimilation tool is used to analyze ground and satellite-based geomagnetic data sets. The dynamics of the Earth's outer core on interannual to decadal timescales is investigated, and new findings on the operation of quasi-geostrophic Magneto-Coriolis waves are reported. An improved ensemble Kalman filter algorithm is introduced, which takes into account cross-correlations between variables, resulting in better stability and reduced computational cost. The updated scheme also allows for the use of observations in different forms, enabling global constraints on core dynamics even at short periods.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
Yi Jiang, Richard Holme, Sheng-Qing Xiong, Yong Jiang, Yan Feng, Hai Yang
Summary: The study introduces new regional models of the Chinese lithospheric field, CLAS, combining satellite-derived models and aeromagnetic survey data. The results show that CLAS models exhibit high correlation with satellite models at low-degree terms and more power at high-degree terms, reflecting more features of the lithospheric field in continental China. Despite some accuracy loss in aeromagnetic data, the models have good agreement with Chinese aeromagnetic data at wavelength down to about 100 km, filling the gap between satellite models and aeromagnetic data.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
G. Ropp, V Lesur
Summary: A series of models of the Earth magnetic field and core surface flow have been estimated from 1999 to 2022 using magnetic satellite and ground observatory data. The models show characteristics similar to previous models, but with higher time resolution. Principal component analysis reveals that the largest flow variations occur at high latitudes and under the western part of the Pacific Ocean. Filtering out longer flow variation periods leads to a filtered azimuthal flow with approximately 7-year periodicities propagating westward. These patterns are mainly present at mid- and equatorial latitudes and are compatible with perturbations in the main flow caused by small columnar flows intersecting the core-mantle boundary.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
L. B. Vital, V. C. Jr Jr Oliveira, V. C. F. Barbosa
Summary: The method proposed in this study utilizes total-field anomaly data to estimate the geometry of a uniformly magnetized 3-D geological source in the subsurface, assuming known total-magnetization direction. By approximating the source with vertically juxtaposed right prisms and implementing radial inversion and Tikhonov regularization, the method allows for stable estimates of the source shape, even in the presence of a strong regional field. Tests with synthetic data and real-world examples show the effectiveness of the method in accurately estimating the geometry of magnetic sources.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
Mark David Wigh, Thomas Mejer Hansen, Arne Dossing
Summary: The study investigates the theoretical possibility of discriminating between unexploded ordnance (UXO) and non-UXO sources by modeling the magnetic dipole moment of ferrous objects. By approximating the volumetric demagnetization factors of rectangular prisms and modeling different UXO as prolate spheroids, comparisons can be made. The inversion process is done within a probabilistic framework with individual prior models assigned to the different objects in terms of shape, size, orientation, and remanent magnetization.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Mark David Wigh, Thomas Mejer Hansen, Arne Dossing
Summary: The study investigates the theoretical possibility of discriminating between unexploded ordnance (UXO) and non-UXO sources by modeling the magnetic dipole moment for ferrous objects of different shapes and sizes. By approximating volumetric demagnetization factors of rectangular prisms and modeling UXO as prolate spheroids, the study aims to compare the demagnetization factors with the magnetic response of a prism. Introducing a UXO prior significantly improves discrimination capabilities by providing expected UXO properties for comparison.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
Mohammad Hossein Ghalehnoee, Abdolhamid Ansari
Summary: Magnetization vector inversion (MVI) is an effective method for identifying magnetic causative bodies, especially when magnetic data are affected by different remanent magnetization. A compact magnetization vector inversion method is proposed in this study, and its reliability is validated through case studies.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Yixiati Dilixiati, Eldar Baykiev, Joerg Ebbing
Summary: A novel approach combining aeromagnetic and satellite data is proposed, involving inversion for magnetic parameters and conversion into spherical harmonics. Testing on Magnetic Anomaly Maps of Australia shows good agreement with satellite data when replacing long-wavelength aeromagnetic data with satellite data.
Article
Geosciences, Multidisciplinary
Alexandre Fournier, Julien Aubert, Vincent Lesur, Guillaume Ropp
Summary: This paper presents a candidate secular variation model for the 13th generation of the International Geomagnetic Reference Field, based on an ensemble of 100 numerical models integrated between 2019.0 and 2025.0. By adjusting 100 different initial conditions extracted from a dynamo simulation to account for the geomagnetic field estimate for 2019.0, the model provides insights into the geomagnetic secular variation up to epoch 2025.0.
EARTH PLANETS AND SPACE
(2021)
Article
Geochemistry & Geophysics
Clemens Kloss, Christopher C. Finlay, Karl M. Laundal, Nils Olsen
Summary: This study presents a new approach to simultaneously estimate a climatological model of the ionospheric field and a model of the internal field in the Earth's core. The new method is able to better account for magnetic signals produced by polar ionospheric currents. The study finds that using satellite data, a new geomagnetic field model can be derived which successfully explains previously unmodelled ionospheric signals.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
Santiago R. Soler, Leonardo Uieda
Summary: The equivalent source technique is effective but computationally expensive for processing gravity and magnetic data. The authors propose two techniques to reduce the computational cost: block-averaging source locations and the gradient-boosted equivalent source algorithm. Through experiments, it is shown that these techniques can produce accurate interpolations efficiently.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
Magnus D. Hammer, Christopher C. Finlay, Nils Olsen
Summary: In this study, local time-series of the magnetic field gradient tensor elements at satellite altitude were derived using a Geomagnetic Virtual Observatory (GVO) approach. The derived gradient element time-series allow for global investigations of spatio-temporal variations in the gradient tensor elements. Evidence for a regional increase event in 2017 was found based on the first time derivative of the gradient tensor elements.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
V Lesur, N. Gillet, M. D. Hammer, M. Mandea
Summary: This paragraph discusses the evidence of fast variations in the Earth's core field observed in magnetic observatory and satellite records. It explains how these variations are identified at the Earth's surface and characterized by satellite data. The paragraph also mentions the extraction of their properties at the core mantle boundary through localized and global modeling processes, with emphasis on their time scales. Finally, it lists the possible types of waves in the liquid outer core that may cause these observed fast variations.
SURVEYS IN GEOPHYSICS
(2022)
Article
Geochemistry & Geophysics
Magnus D. Hammer, Christopher C. Finlay, Nils Olsen
Summary: In this study, local time-series of the magnetic field gradient tensor elements at satellite altitude were derived using a Geomagnetic Virtual Observatory (GVO) approach. The derived gradient element time-series allow for global investigations of spatio-temporal variations in the gradient tensor elements. Evidence for a regional increase event in 2017 was found based on the first time derivative of the gradient tensor elements.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Nils Olsen
Summary: The sensitivity of magnetic measurements taken by satellites in elliptical orbits to the lithospheric magnetic field is studied. The variances of the lithospheric Gauss coefficients for different satellite orbital constellations are compared and analytical expressions for the variances are presented. It is found that low-altitude magnetic data collected by satellites in low-perigee elliptical orbits enable improved global lithospheric field modelling at spatial wavelengths beyond what is currently possible with data from satellites in circular orbits.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geosciences, Multidisciplinary
I Michaelis, K. Styp-Rekowski, J. Rauberg, C. Stolle, M. Korte
Summary: The GOCE satellite, part of ESA's Earth Explorer Program, carries magnetometers for navigation and scientific research on Earth's magnetic field. Pre-processing, calibration, and characterisation steps are performed on the magnetic data to remove artificial perturbations and show the natural evolution and variability of the magnetic field. The data demonstrate good agreement with ground observations and are expected to be useful for lithospheric modelling.
EARTH PLANETS AND SPACE
(2022)
Article
Geosciences, Multidisciplinary
Kevin Styp-Rekowski, Ingo Michaelis, Claudia Stolle, Julien Baerenzung, Monika Korte, Odej Kao
Summary: A machine learning-based approach is proposed in this study to calibrate platform magnetometers using neural networks, improving the quality of magnetic field observations. The calibrated data can be used for reconstructing lithospheric field, observing geomagnetic storms, and improving geomagnetic field models.
EARTH PLANETS AND SPACE
(2022)
Article
Geochemistry & Geophysics
M. Istas, N. Gillet, C. C. Finlay, M. D. Hammer, L. Huder
Summary: In this study, the pygeodyn data assimilation tool is used to analyze ground and satellite-based geomagnetic data sets. The dynamics of the Earth's outer core on interannual to decadal timescales is investigated, and new findings on the operation of quasi-geostrophic Magneto-Coriolis waves are reported. An improved ensemble Kalman filter algorithm is introduced, which takes into account cross-correlations between variables, resulting in better stability and reduced computational cost. The updated scheme also allows for the use of observations in different forms, enabling global constraints on core dynamics even at short periods.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Astronomy & Astrophysics
Theodore E. Sarris, Stelios Tourgaidis, Panagiotis Pirnaris, Dimitris Baloukidis, Konstantinos Papadakis, Christos Psychalas, Stephan Christoph Buchert, Eelco Doornbos, Mark A. Clilverd, Pekka T. Verronen, David Malaspina, Narghes Ahmadi, Iannis Dandouras, Anna Kotova, Wojciech J. Miloch, David Knudsen, Nils Olsen, Octav Marghitu, Tomoko Matsuo, Gang Lu, Aurelie Marchaudon, Alex Hoffmann, Dulce Lajas, Anja Stromme, Matthew Taylor, Anita Aikio, Minna Palmroth, Roderick Heelis, Nickolay Ivchenko, Claudia Stolle, Guram Kervalishvili, Therese Moretto-Jorgensen, Robert Pfaff, Christian Siemes, Pieter Visser, Jose van den Ijssel, Han-Li Liu, Ingmar Sandberg, Constantinos Papadimitriou, Joachim Vogt, Adrian Blagau, Nele Stachlys
Summary: Daedalus MASE is an open-source package of scientific analysis tools for research in the Lower Thermosphere-Ionosphere (LTI), with the ability to assess mission performance and demonstrate closure of objectives. It provides various capabilities related to LTI science and modeling.
FRONTIERS IN ASTRONOMY AND SPACE SCIENCES
(2023)
Review
Astronomy & Astrophysics
Theodoros Sarris, Minna Palmroth, Anita Aikio, Stephan Christoph Buchert, James Clemmons, Mark Clilverd, Iannis Dandouras, Eelco Doornbos, Lindsay Victoria Goodwin, Maxime Grandin, Roderick Heelis, Nickolay Ivchenko, Therese Moretto-Jorgensen, Guram Kervalishvili, David Knudsen, Han-Li Liu, Gang Lu, David M. Malaspina, Octav Marghitu, Astrid Maute, Wojciech J. Miloch, Nils Olsen, Robert Pfaff, Claudia Stolle, Elsayed Talaat, Jeffrey Thayer, Stelios Tourgaidis, Pekka T. Verronen, Masatoshi Yamauchi
Summary: The lower thermosphere-ionosphere (LTI) is a critical transition region between Earth's atmosphere and space. However, its complex interactions between neutral and charged constituents remain poorly characterized due to the lack of in situ measurements. The quantification of key processes in the 100-200 km altitude range is essential for improving atmospheric models and space weather prediction capabilities.
FRONTIERS IN ASTRONOMY AND SPACE SCIENCES
(2023)
Article
Geosciences, Multidisciplinary
Yi Jiang, Nils Olsen, JiaMing Ou, Qing Yan
Summary: A proposal for a future constellation of at least four geomagnetic satellites has been made to continue high-quality geomagnetic observations. This paper presents a simulation of two satellites' orbits for two years and investigates the sensitivity of lithospheric magnetic field modelling to data collected from various satellite orbits. The results show that the planned lower perigee of the new satellites' orbits allows for data collection at unprecedentedly lower altitudes, improving the spatial resolution of satellite-derived lithospheric field models.
EARTH AND PLANETARY PHYSICS
(2023)
Article
Geochemistry & Geophysics
Nils Olsen, Dhananjay Ravat, Michael E. Purucker
Summary: We propose a new technique for reducing uncertainties in lithospheric magnetic field observations over the Earth. This technique improves the estimation of the depth-integrated magnetic susceptibility of the crust compared to previous methods. Instead of using observations at specific locations, we directly model Gauss coefficients of the lithospheric magnetic field and utilize an a-priori initial lithospheric thickness model to handle magnetic annihilators. Our method is applied to the LCS-1 magnetic field model derived from satellite data and is suitable for regions dominated by induced magnetization.
EARTH AND PLANETARY SCIENCE LETTERS
(2023)
Article
Geosciences, Multidisciplinary
Yuri Y. Y. Shprits, Ingo Michaelis, Dedong Wang, Hayley Allison, Ruggero Vasile, Andrei Runov, Alexander Drozdov, Christopher T. Russell, Vladimir Kalegaev, Artem Smirnov
Summary: This study used measurements from the ELFIN-L suit of instruments on the Lomonosov spacecraft to distinguish between stably trapped and drift loss cone electrons. The results show that the loss at MeV energies mainly occurs on the dawn-side, consistent with loss induced by chorus waves.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Review
Environmental Sciences
Christopher C. C. Finlay, Nicolas Gillet, Julien Aubert, Philip W. W. Livermore, Dominique Jault
Summary: The turbulent motions of liquid metal in Earth's outer core generate the geomagnetic field. Observations and simulations have shown that the present-day core motions are dominated by a planetary-scale gyre, a jet in the northern polar region, and waves involving the magnetic field. In this review, we explore the dynamics of these core features and discuss their impact on the Earth's magnetism and rotation.
NATURE REVIEWS EARTH & ENVIRONMENT
(2023)
Article
Engineering, Aerospace
Benoit Tezenas du Montcel, Arnaud Trouche, Ingo Michaelis, Benjamin Jeanty-Ruard, Michael Wutzig, Julien Forest, Yuri Y. Shprits
Summary: The Prediction of Adverse effects of Geomagnetic storms and Energetic Radiation project aims to provide a framework for space weather forecasts and related effect forecasts. It utilizes innovative concepts to evaluate the charging risk for spacecraft on GEO and MEO orbits by combining different charging models and simulation of the radiation belt. The project also develops internal charging modeling chains for risk evaluation and reproduction of charging events.
ADVANCES IN SPACE RESEARCH
(2023)
Article
Geochemistry & Geophysics
Clemens Kloss, Christopher C. Finlay, Karl M. Laundal, Nils Olsen
Summary: This study presents a new approach to simultaneously estimate a climatological model of the ionospheric field and a model of the internal field in the Earth's core. The new method is able to better account for magnetic signals produced by polar ionospheric currents. The study finds that using satellite data, a new geomagnetic field model can be derived which successfully explains previously unmodelled ionospheric signals.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
