| Alken P, Thébault E, Beggan CD, Amit H, Aubert J, Baerenzung J, Bondar TN, Brown WJ, Califf S, Chambodut A, Chulliat A, Cox GA, Finlay CC, Fournier A, Gillet N, Grayver A, Hammer MD, Holschneider M, Huder L, Hulot G, Jager T, Kloss C, Korte M, Kuang W, Kuvshinov A, Langlais B, Léger JM, Lesur V, Livermore PW, Lowes FJ, Macmillan S, Magnes W, Mandea M, Marsal S, Matzka J, Metman MC, Minami T, Morschhauser A, Mound JE, Nair M, Nakano S, Olsen N, Pavón-Carrasco FJ, Petrov VG, Ropp G, Rother M, Sabaka TJ, Sanchez S, Saturnino D, Schnepf NR, Shen X, Stolle C, Tangborn A, Tøffner-Clausen L, Toh H, Torta JM, Varner J, Vervelidou F, Vigneron P, Wardinski I, Wicht J, Woods A, Yang Y, Zeren Z and Zhou B (2021),
"International Geomagnetic Reference Field: the thirteenth generation", Earth, Planets and Space. Vol. 73(1), pp. 49. |
| Abstract: In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period. |
BibTeX:
@article{Alken:2021,
author = {Alken, P. and Thébault, E. and Beggan, C. D. and Amit, H. and Aubert, J. and Baerenzung, J. and Bondar, T. N. and Brown, W. J. and Califf, S. and Chambodut, A. and Chulliat, A. and Cox, G. A. and Finlay, C. C. and Fournier, A. and Gillet, N. and Grayver, A. and Hammer, M. D. and Holschneider, M. and Huder, L. and Hulot, G. and Jager, T. and Kloss, C. and Korte, M. and Kuang, W. and Kuvshinov, A. and Langlais, B. and Léger, J. -M. and Lesur, V. and Livermore, P. W. and Lowes, F. J. and Macmillan, S. and Magnes, W. and Mandea, M. and Marsal, S. and Matzka, J. and Metman, M. C. and Minami, T. and Morschhauser, A. and Mound, J. E. and Nair, M. and Nakano, S. and Olsen, N. and Pavón-Carrasco, F. J. and Petrov, V. G. and Ropp, G. and Rother, M. and Sabaka, T. J. and Sanchez, S. and Saturnino, D. and Schnepf, N. R. and Shen, X. and Stolle, C. and Tangborn, A. and Tøffner-Clausen, L. and Toh, H. and Torta, J. M. and Varner, J. and Vervelidou, F. and Vigneron, P. and Wardinski, I. and Wicht, J. and Woods, A. and Yang, Y. and Zeren, Z. and Zhou, B.},
title = {International Geomagnetic Reference Field: the thirteenth generation},
journal = {Earth, Planets and Space},
year = {2021},
volume = {73},
number = {1},
pages = {49},
doi = {10.1186/s40623-020-01288-x}
}
|
| Alken P, Thébault E, Beggan CD, Aubert J, Baerenzung J, Brown WJ, Califf S, Chulliat A, Cox GA, Finlay CC, Fournier A, Gillet N, Hammer MD, Holschneider M, Hulot G, Korte M, Lesur V, Livermore PW, Lowes FJ, Macmillan S, Nair M, Olsen N, Ropp G, Rother M, Schnepf NR, Stolle C, Toh H, Vervelidou F, Vigneron P and Wardinski I (2021),
"Evaluation of candidate models for the 13th generation International Geomagnetic Reference Field", Earth, Planets and Space. Vol. 73(1), pp. 48. |
| Abstract: In December 2019, the 13th revision of the International Geomagnetic Reference Field (IGRF) was released by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD. This revision comprises two new spherical harmonic main field models for epochs 2015.0 (DGRF-2015) and 2020.0 (IGRF-2020) and a model of the predicted secular variation for the interval 2020.0 to 2025.0 (SV-2020-2025). The models were produced from candidates submitted by fifteen international teams. These teams were led by the British Geological Survey (UK), China Earthquake Administration (China), Universidad Complutense de Madrid (Spain), University of Colorado Boulder (USA), Technical University of Denmark (Denmark), GFZ German Research Centre for Geosciences (Germany), Institut de physique du globe de Paris (France), Institut des Sciences de la Terre (France), Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (Russia), Kyoto University (Japan), University of Leeds (UK), Max Planck Institute for Solar System Research (Germany), NASA Goddard Space Flight Center (USA), University of Potsdam (Germany), and Universitéde Strasbourg (France). The candidate models were evaluated individually and compared to all other candidates as well to the mean, median and a robust Huber-weighted model of all candidates. These analyses were used to identify, for example, the variation between the Gauss coefficients or the geographical regions where the candidate models strongly differed. The majority of candidates were sufficiently close that the differences can be explained primarily by individual modeling methodologies and data selection strategies. None of the candidates were so different as to warrant their exclusion from the final IGRF-13. The IAGA V-MOD task force thus voted for two approaches: the median of the Gauss coefficients of the candidates for the DGRF-2015 and IGRF-2020 models and the robust Huber-weighted model for the predictive SV-2020-2025. In this paper, we document the evaluation of the candidate models and provide details of the approach used to derive the final IGRF-13 products. We also perform a retrospective analysis of the IGRF-12 SV candidates over their performance period (2015–2020). Our findings suggest that forecasting secular variation can benefit from combining physics-based core modeling with satellite observations. |
BibTeX:
@article{Alken:2021b,
author = {Alken, P. and Thébault, E. and Beggan, C. D. and Aubert, J. and Baerenzung, J. and Brown, W. J. and Califf, S. and Chulliat, A. and Cox, G. A. and Finlay, C. C. and Fournier, A. and Gillet, N. and Hammer, M. D. and Holschneider, M. and Hulot, G. and Korte, M. and Lesur, V. and Livermore, P. W. and Lowes, F. J. and Macmillan, S. and Nair, M. and Olsen, N. and Ropp, G. and Rother, M. and Schnepf, N. R. and Stolle, C. and Toh, H. and Vervelidou, F. and Vigneron, P. and Wardinski, I.},
title = {Evaluation of candidate models for the 13th generation International Geomagnetic Reference Field},
journal = {Earth, Planets and Space},
year = {2021},
volume = {73},
number = {1},
pages = {48},
doi = {10.1186/s40623-020-01281-4}
}
|
| Fournier A, Aubert J, Lesur V and Ropp G (2021),
"A secular variation candidate model for IGRF-13 based on Swarm data and ensemble inverse geodynamo modelling", Earth, Planets and Space. Vol. 73(1), pp. 43. |
| Abstract: This paper describes the design of a candidate secular variation model for the 13th generation of the International Geomagnetic Reference Field. This candidate is based upon the integration of an ensemble of 100 numerical models of the geodynamo between epochs 2019.0 and 2025.0. The only difference between each ensemble member lies in the initial condition that is used for the numerical integration, all other control parameters being fixed. An initial condition is defined as follows: an estimate of the magnetic field and its rate-of-change at the core surface for 2019.0 is obtained from a year (2018.5–2019.5) of vector Swarm data. This estimate (common to all ensemble members) is subject to prior constraints: the statistical properties of the numerical dynamo model for the main geomagnetic field and its secular variation, and prescribed covariances for the other sources. One next considers 100 three-dimensional core states (in terms of flow, buoyancy and magnetic fields) extracted at different discrete times from a dynamo simulation that is not constrained by observations, with the time distance between each state exceeding the dynamo decorrelation time. Each state is adjusted (in three dimensions) in order to take the estimate of the geomagnetic field and its rate-of-change for 2019.0 into account. This methodology provides 100 different initial conditions for subsequent numerical integration of the dynamo model up to epoch 2025.0. Focussing on the 2020.0–2025.0 time window, we use the median average rate-of-change of each Gauss coefficient of the ensemble and its statistics to define the geomagnetic secular variation over that time frame and its uncertainties. |
BibTeX:
@article{Fournier:2021,
author = {Fournier, Alexandre and Aubert, Julien and Lesur, Vincent and Ropp, Guillaume},
title = {A secular variation candidate model for IGRF-13 based on Swarm data and ensemble inverse geodynamo modelling},
journal = {Earth, Planets and Space},
year = {2021},
volume = {73},
number = {1},
pages = {43},
doi = {10.1186/s40623-020-01309-9}
}
|
| Lesur V, Gillet N, Hammer MD and Mandea M (2021),
"Rapid variations of Earth's core magnetic field", Surveys in Geophysics. |
BibTeX:
@article{Lesur:2021,
author = {Lesur, Vincent and Gillet, Nicolas and Hammer, Magnus Danel and Mandea, Mioara},
title = {Rapid variations of Earth's core magnetic field},
journal = {Surveys in Geophysics},
year = {2021},
note = {In Press.},
doi = {10.1007/s10712-021-09662-4}
}
|
| Baerenzung J, Holschneider M, Wicht J, Lesur V and Sanchez S (2020),
"The Kalmag model as a candidate for IGRF-13", Earth, Planets and Space. Vol. 72(1), pp. 163. |
| Abstract: We present a new model of the geomagnetic field spanning the last 20 years and called Kalmag. Deriving from the assimilation of CHAMP and Swarm vector field measurements, it separates the different contributions to the observable field through parameterized prior covariance matrices. To make the inverse problem numerically feasible, it has been sequentialized in time through the combination of a Kalman filter and a smoothing algorithm. The model provides reliable estimates of past, present and future mean fields and associated uncertainties. The version presented here is an update of our IGRF candidates; the amount of assimilated data has been doubled and the considered time window has been extended from [2000.5, 2019.74] to [2000.5, 2020.33]. |
BibTeX:
@article{Baerenzung:2020,
author = {Baerenzung, Julien and Holschneider, Matthias and Wicht, Johannes and Lesur, Vincent and Sanchez, Sabrina},
title = {The Kalmag model as a candidate for IGRF-13},
journal = {Earth, Planets and Space},
year = {2020},
volume = {72},
number = {1},
pages = {163},
doi = {10.1186/s40623-020-01295-y}
}
|
| Lesur V and Vervelidou F (2020),
"Retrieving lithospheric magnetisation distribution from magnetic field models", Geophys. J. Int.. Vol. 220, pp. 981-995. |
| Abstract: We investigate to which extent the radially averaged magnetization of the lithosphere can be recovered from the information content of a spherical harmonic model of the generated magnetic field when combined with few simple hypotheses. The results obtained show firstly that a hypothesis of magnetization induced by a field of internal origin, even over a localized area, is not sufficient to recover uniquely the radially averaged magnetization and, secondly, that this magnetization can be recovered when a constant magnetization direction is assumed. An algorithm to recover the magnetization direction and distribution is then described and tested over a synthetic example. It requires to introduce a cost function that vanishes when estimated in a system of coordinates with its Z-axis aligned with the magnetization direction. Failing to find a vanishingly small value for the cost function is an indication that a constant magnetization direction is not a valid hypothesis for the studied magnetic field model. The range of magnetization directions that are compatible with the magnetic field model and a given noise level, can also be estimated. The whole process is illustrated by analysing a local, isolated maximum of the Martian magnetic field. |
BibTeX:
@article{Lesur:2019,
author = {Lesur, V. and Vervelidou, F.},
title = {Retrieving lithospheric magnetisation distribution from magnetic field models},
journal = {Geophys. J. Int.},
year = {2020},
volume = {220},
pages = {981--995},
note = {Published online in October 2019},
doi = {10.1093/gji/ggz471}
}
|
| Mandea M and Chambodut A (2020),
"Geomagnetic Field Processes and Their Implications for Space Weather", Surveys in Geophysics. Vol. 41(6), pp. 1611-1627. |
| Abstract: Understanding the magnetic environment of our planet and the geomagnetic field changes in time and space is a very important issue for assessing the Sun–Earth interactions. All changes in solar activity impact the delicate balance between influences of interplanetary magnetic field and of geomagnetic field. The most dynamic events eventually result in disturbances in the magnitude and direction of the Earth’s magnetic field and therefore impact our planet and its magnetosphere as a whole. The dynamics of the ionosphere and thermosphere during magnetic storms and substorms involves the heating, expansion, and composition changes at high latitudes, but also the surface-level response in terms of geomagnetically induced currents and other geomagnetic and geoelectric disturbances. Here, we provide a short overview of the current knowledge of the Earth’s magnetic field, its present shape and the way it responds to external forces. The main aim of the paper is not to present the complexity of the space weather processes, but rather to bring the attention of the geohazard community to the possible dramatic effects of space weather events. For this, the paper highlights some societal implications of space weather on our increasingly technology-dependent society, including some possible effects of geomagnetically induced currents, the disruption of satellite communications and navigation, and risks of radiation damage both in space and in aviation. |
BibTeX:
@article{Mandea:2020,
author = {Mandea, Mioara and Chambodut, Aude},
title = {Geomagnetic Field Processes and Their Implications for Space Weather},
journal = {Surveys in Geophysics},
year = {2020},
volume = {41},
number = {6},
pages = {1611--1627},
url = {10.1007/s10712-020-09598-1},
doi = {10.1007/s10712-020-09598-1}
}
|
| Minami T, Nakano S, Lesur V, Takahashi F, Matsushima M, Shimizu H, Nakashima R, Taniguchi H and Toh H (2020),
"A candidate secular variation model for IGRF-13 based on MHD dynamo simulation and data assimilation, En4dVar", Earth Planets and Space. |
| Abstract: We have submitted a secular variation (SV) candidate model for the thirteenth generation of International Geomagnetic Reference Field model (IGRF-13) using a data assimilation scheme and a magnetohydrodynamic (MHD) dynamo simulation code. This is the first contribution to the IGRF community from research groups in Japan. A geomagnetic field model derived from magnetic observatory hourly means, and CHAMP and Swarm-A satellite data, has been used as input data to the assimilation scheme. We adopt an ensemble-based assimilation scheme, called four-dimensional ensemble-based variational method (4DEnVar), which linearizes outputs of MHD dynamo simulation with respect to the deviation from a dynamo state vector at an initial condition. The data vector for the assimilation consists of the poloidal scalar potential of the geomagnetic field at the core surface and flow velocity field slightly below the core surface. Dimensionless time of numerical geodynamo is adjusted to the actual time by comparison of secular variation time scales. For SV prediction, we first generate an ensemble of dynamo simulation results from a free dynamo run. We then assimilate the ensemble to the data with a 10-year assimilation window through iterations, and finally forecast future SV by the weighted sum of the future extension parts of the ensemble members. Hindcast of the method for the assimilation window from 2004.50 to 2014.25 confirms that the linear approximation holds for 10-year assimilation window with our iterative ensemble renewal method. We demonstrate that the forecast performance of our data assimilation and forecast scheme is comparable with that of IGRF-12 by comparing data misfits 4.5 years after the release epoch. For estimation of our IGRF-13SV candidate model, we set assimilation window from 2009.50 to 2019.50. We generate our final SV candidate model by linear fitting for the weighted sum of the ensemble MHD dynamo simulation members from 2019.50 to 2025.00. We derive errors of our SV candidate model by one standard deviation of SV histograms based on all the ensemble members. |
BibTeX:
@article{Minami:2020,
author = {Minami, T. and Nakano, S. and Lesur, V. and Takahashi, F. and Matsushima, M. and Shimizu, H. and Nakashima, R. and Taniguchi, H. and Toh, H.},
title = {A candidate secular variation model for IGRF-13 based on MHD dynamo simulation and data assimilation, En4dVar},
journal = {Earth Planets and Space},
year = {2020},
doi = {10.1186/s40623-020-01253-8}
}
|
| Ropp G, Lesur V, Baerenzung J and Holschneider M (2020),
"Sequential modelling of the Earth's core magnetic field", Earth, Planets and Space. |
| Abstract: We describe a new, original approach to the modelling of the Earth’s magnetic field. The overall objective of this study is to reliably render fast variations of the core field and its secular variation. This method combines a sequential modelling approach, a Kalman filter, and a correlation-based modelling step. Sources that most significantly contribute to the field measured at the surface of the Earth are modelled. Their separation is based on strong prior information on their spatial and temporal behaviours. We obtain a time series of model distributions which display behaviours similar to those of recent models based on more classic approaches, particularly at large temporal and spatial scales. Interesting new features and periodicities are visible in our models at smaller time and spatial scales. An important aspect of our method is to yield reliable error bars for all model parameters. These errors, however, are only as reliable as the description of the different sources and the prior information used are realistic. Finally, we used a slightly different version of our method to produce candidate models for the thirteenth edition of the International Geomagnetic Reference Field. |
BibTeX:
@article{Ropp:2020,
author = {Ropp, G. and Lesur, V. and Baerenzung, J. and Holschneider, M.},
title = {Sequential modelling of the Earth's core magnetic field},
journal = {Earth, Planets and Space},
year = {2020},
doi = {10.1186/s40623-020-01230-1}
}
|
| Wardinski I, Amit H, Langlais B and Thébault E (2020),
"The internal structure of Mercury’s core inferred from magnetic observations", Earth and Space Science Open Archive. , pp. 27. |
| Abstract: Previous models of Mercury's core magnetic field based on high altitude data from first MESSENGER flybys revealed an axisymmetric. Here we use low altitude MESSENGER data covering the entire mission period to construct spherical harmonic models based on various spatial norms. Although we find a dominantly axisymmetric field, our models nevertheless include detectable deviations from axisymmetry. These non-axisymmetric features appear at high latitudes, resembling intense geomagnetic flux patches at Earth's core-mantle boundary. Based on this core field morphology, we then attempt to infer Mercury's internal structure. More specifically, assuming that Mercury's high-latitude non-axisymmetric features are concentrated by downwellings at the edge of the planet's inner core tangent cylinder, and accounting for the presence of a stably stratified layer at the top of Mercury's core, we establish a relation between the inner core size and the thickness of the stratified layer. Considering plausible ranges, we propose that Mercury's inner core size is about 500-660 km, which corresponds to a stratified layer thickness of 880-500 km, respectively. |
BibTeX:
@article{Wardinski:2020,
author = {Wardinski, I and Amit, H and Langlais, B and Thébault, E},
title = {The internal structure of Mercury’s core inferred from magnetic observations},
journal = {Earth and Space Science Open Archive},
year = {2020},
pages = {27},
doi = {10.1002/essoar.10503385.1}
}
|
| Wardinski I, Saturnino D, Amit H, Chambodut A, Langlais B, Mandea M and Thebault E (2020),
"Geomagnetic core field models and secular variation forecasts for the 13th International Geomagnetic Reference Field (IGRF-13)", Earth, Planets and Space. Vol. 72(1), pp. 1-22. SpringerOpen. |
| Abstract: Observations of the geomagnetic field taken at Earth’s surface and at satellite altitude are combined to construct continuous models of the geomagnetic field and its secular variation from 1957 to 2020. From these parent models, we derive candidate main field models for the epochs 2015 and 2020 to the 13th generation of the International Geomagnetic Reference Field (IGRF). The secular variation candidate model for the period 2020–2025 is derived from a forecast of the secular variation in 2022.5, which results from a multi-variate singular spectrum analysis of the secular variation from 1957 to 2020. |
BibTeX:
@article{Wardinski2020,
author = {Wardinski, Ingo and Saturnino, Diana and Amit, Hagay and Chambodut, Aude and Langlais, Benoit and Mandea, Mioara and Thebault, Erwan},
title = {Geomagnetic core field models and secular variation forecasts for the 13th International Geomagnetic Reference Field (IGRF-13)},
journal = {Earth, Planets and Space},
publisher = {SpringerOpen},
year = {2020},
volume = {72},
number = {1},
pages = {1--22},
doi = {10.1186/s40623-020-01254-7}
}
|
| Lesur V and Thébault E (2019),
"The Global Lithospheric Magnetic Field: World Magnetic Anomaly Maps and Models", In Geomagnetism, Aeronomy and Space Weather. Cambridge University Press. |
| Abstract: The magnetic field generated in the Earth’s lithosphere carries information on the Earth history and tectonics. It is therefore worthwhile studying, but gathering magnetic data for this purpose is a task requiring time and significant ressources. This has been the main objective of the World Digital Magnetic Anomaly Map (WDMAM) project. We recall here the main steps that led to the first and second versions of the map. We further discuss the models that have been derived from the map, and finally describe recent works to interpret these models in term of magnetisation of the crust. We see these recent developments as major steps forward for an efficient exploitation of the magnetic data collected near the surface of the Earth. |
BibTeX:
@inbook{Lesur:2018,
author = {Lesur, V. and Thébault, E.},
editor = {Korte, M.},
title = {The Global Lithospheric Magnetic Field: World Magnetic Anomaly Maps and Models},
booktitle = {Geomagnetism, Aeronomy and Space Weather},
publisher = {Cambridge University Press},
year = {2019},
doi = {10.1017/9781108290135.011}
}
|
| Wardinski I, Langlais B. and Thébault E (2019),
"Correlated time‐varying magnetic fields and the core size of mercury.", Journal of Geophysical Research: Planets. Vol. 124, pp. 2178– 2197. |
| Abstract: Mercury is characterized by a very peculiar magnetic field, as it was revealed by the MESSENGER mission. Its internal component is highly axisymmetric, dominated by the dipole, and very weak. This in turns leads to a very dynamic magnetosphere. It is known that there exist relationships between the internally generated field and the external field, although their dynamics are complex. In this study we derive steady and time‐varying spherical harmonic models of Mercury's magnetic field using MESSENGER measurements and interpret these models both in terms of correlated features and of the internal structure of Mercury. The influence of the hemispheric data distribution of MESSENGER is evaluated to grant the robustness of our models. We find a quadrupole‐to‐dipole ratio of 0.27 for the steady magnetic field. The time‐varying models reveal periodic and highly correlated temporal variations of internal and external origins. This argues for externally inducing and internally induced sources. The main period is 88 days, the orbital period of Mercury around the Sun. There is no measurable time lag between variations of external and internal magnetic fields, which place an upper limit of 1 S/m for the mantle conductivity. Finally, the compared amplitudes of external and internal time‐varying field lead to an independent (from gravity studies) estimate of the conductive core radius, at 2,060 ± 22 km. These analyses will be further completed with the upcoming BepiColombo mission and its magnetic field experiment, but the presented results already lift the veil on some of the magnetic oddities at Mercury. |
BibTeX:
@article{Wardinski:2019b,
author = {Wardinski, I. and Langlais, B., and Thébault, E.},
title = {Correlated time‐varying magnetic fields and the core size of mercury.},
journal = {Journal of Geophysical Research: Planets},
year = {2019},
volume = {124},
pages = {2178– 2197},
doi = {10.1029/2018JE005835}
}
|
| Wardinski I and Thébault E (2019),
"Modelling Internal and External Geomagnetic Fields Using Satellite Data", In Geomagnetism, Aeronomy and Space Weather: A Journey from the Earth's Core to the Sun. Cambridge , pp. 84–97. Cambridge University Press. |
| Abstract: Earth’s magnetic field as it is measured by satellite missions is mainly generated by the dynamo process in the liquid outer core of the Earth. Other sources that are also regarded as internal are the static lithospheric field due to crustal magnetisation, the induced field in the mantle, lithospheric and Oceanic induced fields. The latter are generated by secondary dynamo processes, where the motion of conductive seawater in an ambient magnetic field induces a magnetic field. External fields originate in Earth’s magnetosphere and ionosphere. All these individual source fields differ in their strength, they spatially overlap and vary on similar time scales. These characteristics are challenging in resolving the processes that are related to these sources. The aim of this article is to provide a brief review of current geomagnetic field modelling techniques, which are based on measurements of Earth’s magnetic field at satellite altitude. Furthermore, we discuss different applications of the field modelling techniques and their limitations. |
BibTeX:
@incollection{Wardinski:2019,
author = {Wardinski, I. and Thébault, E.},
editor = {Mandea, Mioara and Korte, Monika and Yau, Andrew and Petrovsky, Eduard},
title = {Modelling Internal and External Geomagnetic Fields Using Satellite Data},
booktitle = {Geomagnetism, Aeronomy and Space Weather: A Journey from the Earth's Core to the Sun},
publisher = {Cambridge University Press},
year = {2019},
pages = {84–97},
doi = {10.1017/9781108290135.008}
}
|
| Astafyeva E, Zakharenkova I, Hozumi K, Alken P, Coïsson P, Hairston MR and Coley WR (2018),
"Study of the Equatorial and Low-Latitude Electrodynamic and Ionospheric Disturbances During the 22–23 June 2015 Geomagnetic Storm Using Ground-Based and Spaceborne Techniques", Journal of Geophysical Research: Space Physics. Vol. 123(3), pp. 2424-2440. |
| Abstract: Abstract We use a set of ground-based instruments (Global Positioning System receivers, ionosondes, magnetometers) along with data of multiple satellite missions (Swarm, C/NOFS, DMSP, GUVI) to analyze the equatorial and low-latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22–23 June 2015, which is the second largest storm in the current solar cycle. Our results show that at the beginning of the storm, the equatorial electrojet (EEJ) and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields (PPEF). The PPEF were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside, and downward drift on the nightside. Furthermore, about 45 min after the storm commencement, the interplanetary magnetic field (IMF) Bz component turned northward, leading to the EEJ changing sign to westward, and to overall decrease of the vertical total electron content (VTEC) and electron density on the dayside. At the end of the main phase of the storm, and with the second long-term IMF Bz southward turn, we observed several oscillations of the EEJ, which led us to conclude that at this stage of the storm, the disturbance dynamo effect was already in effect, competing with the PPEF and reducing it. Our analysis showed no significant upward or downward plasma motion during this period of time; however, the electron density and the VTEC drastically increased on the dayside (over the Asian region). We show that this second positive storm was largely influenced by the disturbed thermospheric conditions. |
BibTeX:
@article{Astafyeva:2018,
author = {Astafyeva, E. and Zakharenkova, I. and Hozumi, K. and Alken, P. and Coïsson, P. and Hairston, M. R. and Coley, W. R.},
title = {Study of the Equatorial and Low-Latitude Electrodynamic and Ionospheric Disturbances During the 22–23 June 2015 Geomagnetic Storm Using Ground-Based and Spaceborne Techniques},
journal = {Journal of Geophysical Research: Space Physics},
year = {2018},
volume = {123},
number = {3},
pages = {2424-2440},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JA024981},
doi = {10.1002/2017JA024981}
}
|
| Baerenzung J, Holschneider M, Wicht J, Sanchez S and Lesur V (2018),
"Modeling and predicting the short term evolution of the Geomagnetic field", Journal of Geophysical Research: Solid Earth. Vol. 123 |
| Abstract: We propose a reduced dynamical system describing the coupled evolution of fluid flow and magnetic field at the top of the Earth's core between the years 1900 and 2014. The flow evolution is modeled with a first‐order autoregressive process, while the magnetic field obeys the classical frozen flux equation. An ensemble Kalman filter algorithm serves to constrain the dynamics with the geomagnetic field and its secular variation given by the COV‐OBS.x1 model. Using a large ensemble with 40,000 members provides meaningful statistics including reliable error estimates. The model highlights two distinct flow scales. Slowly varying large‐scale elements include the already documented eccentric gyre. Localized short‐lived structures include distinctly ageostophic features like the high‐latitude polar jet on the Northern Hemisphere. Comparisons with independent observations of the length‐of‐day variations not only validate the flow estimates but also suggest an acceleration of the geostrophic flows over the last century. Hindcasting tests show that our model outperforms simpler predictions bases (linear extrapolation and stationary flow). The predictability limit, of about 2,000 years for the magnetic dipole component, is mostly determined by the random fast varying dynamics of the flow and much less by the geomagnetic data quality or lack of small‐scale information. |
BibTeX:
@article{Baerenzung:2018,
author = {Baerenzung, J. and Holschneider, M. and Wicht, J. and Sanchez, S. and Lesur, V.},
title = {Modeling and predicting the short term evolution of the Geomagnetic field},
journal = {Journal of Geophysical Research: Solid Earth},
year = {2018},
volume = {123},
doi = {10.1029/2017JB015115}
}
|
| Morschhauser A, Vervelidou F, Thomas P, Grott M, Lesur V and Gilder S (2018),
"Mars' Crustal Magnetic Field", In Magnetic Fields in the Solar System. Vol. 448, pp. 331-353. Springer International Publishing AG. |
| Abstract: Fossil magnetic fields within the Martian crust record the history of the planet’s ancient dynamo and hence retain valuable information on the thermal and chemical evolution of Mars. In order to decode this information, we have derived a spherical harmonic model of the crustal magnetic field. This model was derived from satellite vector magnetometer data, and allows to study the crustal magnetic field at high resolution down to surface altitudes. Based on this model, we calculate the required magnetization of the Martian crust, and discuss how the resulting strong magnetization might be explained. Further, we study the magnetization of impact craters and volcanoes, and conclude that the Martian core dynamo shut down most probably in the Noachian, at about 4.1 Gyr ago. Finally, we address the derivation of magnetic paleopole positions. In a first step, we use synthetic tests in order to outline under which constraints paleopole positions can be determined from satellite measurements. In a second step, we use these insights to present a scheme to estimate paleopole positions including an assessment of their underlying uncertainties. |
BibTeX:
@inbook{Morschhauser:2018,
author = {Morschhauser, A. and Vervelidou, F. and Thomas, P. and Grott, M. and Lesur, V. and Gilder, S.A.},
editor = {Luehr, H. and Wicht, J. and Gilder, S.A. and Holschneider, M.},
title = {Mars' Crustal Magnetic Field},
booktitle = {Magnetic Fields in the Solar System},
publisher = {Springer International Publishing AG},
year = {2018},
volume = {448},
pages = {331-353},
doi = {10.1007/978-3-319-64292-5_12}
}
|
| Prokhorov B, Foerster M, Lesur V, Namgaladze AA, Holschneider M and Stolle C (2018),
"Modeling the Ionospheric Current System and Calculating Its contribution to the Earth's Magnetic Field", In Magnetic Fields in the Solar System. Vol. 448(10), pp. 263-292. Springer International Publishing AG. |
| Abstract: The additional magnetic field produced by the ionospheric current system is a part of the Earth’s magnetic field. This current system is a highly variable part of a global electric circuit. The solar wind and interplanetary magnetic field (IMF) interaction with the Earth’s magnetosphere is the external driver for the global electric circuit in the ionosphere. The energy is transferred via the field-aligned currents (FACs) to the Earth’s ionosphere. The interactions between the neutral and charged particles in the ionosphere lead to the so-called thermospheric neutral wind dynamo which represents the second important driver for the global current system. Both processes are components of the magnetosphere–ionosphere–thermosphere (MIT) system, which depends on solar and geomagnetic conditions, and have significant seasonal and UT variations. The modeling of the global dynamic Earth’s ionospheric current system is the first aim of this investigation. For our study, we use the Potsdam version of the Upper Atmosphere Model (UAM-P). The UAM is a first-principle, time-dependent, and fully self-consistent numerical global model. The model includes the thermosphere, ionosphere, plasmasphere, and inner magnetosphere as well as the electrodynamics of the coupled MIT system for the altitudinal range from 80 (60) km up to the 15 Earth radii. The UAM-P differs from the UAM by a new electric field block. For this study, the lower latitudinal and equatorial electrodynamics of the UAM-P model was improved. The calculation of the ionospheric current system’s contribution to the Earth’s magnetic field is the second aim of this study. We present the method, which allows computing the additional magnetic field inside and outside the current layer as generated by the space current density distribution using the Biot-Savart law. Additionally, we perform a comparison of the additional magnetic field calculation using 2D (equivalent currents) and 3D current distribution. |
BibTeX:
@inbook{Prokhorov:2018,
author = {Prokhorov, B. and Foerster, M. and Lesur, V. and Namgaladze, A. A. and Holschneider, M. and Stolle, C.},
editor = {Luehr, H. and Wicht, J. and Gilder, S.A. and Holschneider, M.},
title = {Modeling the Ionospheric Current System and Calculating Its contribution to the Earth's Magnetic Field},
booktitle = {Magnetic Fields in the Solar System},
publisher = {Springer International Publishing AG},
year = {2018},
volume = {448},
number = {10},
pages = {263-292},
doi = {10.1007/978-3-319-64292-5_10}
}
|
| Soloviev A, Lesur V and Kudin D (2018),
"On the feasibility of routine baseline improvement in processing of geomagnetic observatory data", Earth, Planets and Space. Vol. 70(1), pp. 16. |
| Abstract: We propose a new approach to the calculation of regular baselines at magnetic observatories. The proposed approach is based on the simultaneous analysis of the irregular absolute observations and the continuous time-series deltaF, widely used for estimating the data quality. The systematic deltaF analysis allows to take into account all available information about the operation of observatory instruments (i.e., continuous records of the field variations and its modulus) in the intervals between the times of absolute observations, as compared to the traditional baseline calculation where only spot values are considered. To establish a connection with the observed spot baseline values, we introduce a function for approximate evaluation of the intermediate baseline values. An important feature of the algorithm is its quantitative estimation of the resulting data precision and thus determination of the problematic fragments in raw data. We analyze the robustness of the algorithm operation using synthetic data sets. We also compare baselines and definitive data derived by the proposed algorithm with those derived by the traditional approach using Saint Petersburg observatory data, recorded in 2015 and accepted by INTERMAGNET. It is shown that the proposed method allows to essentially improve the resulting data quality when baseline data are not good enough. The obtained results prove that the baseline variability in time might be quite rapid. |
BibTeX:
@article{Soloviev:2018,
author = {Soloviev, Anatoly and Lesur, Vincent and Kudin, Dmitry},
title = {On the feasibility of routine baseline improvement in processing of geomagnetic observatory data},
journal = {Earth, Planets and Space},
year = {2018},
volume = {70},
number = {1},
pages = {16},
url = {https://doi.org/10.1186/s40623-018-0786-8},
doi = {10.1186/s40623-018-0786-8}
}
|
| Vervelidou F and Lesur V (2018),
"Unveiling Earth's hidden magnetisation", Geophysical Research Letters. Vol. 45(12), pp. 283-292. |
| Abstract: Rock magnetization carries information about rocks' properties, Earth's tectonic history, and evolution of its core magnetic field. One way to study Earth's magnetization is through the magnetic signal it generates, known as the lithospheric magnetic field. Although there exist global lithospheric magnetic field models of high spatial resolution, this path has not yet been very fruitful because of an important limitation: only part of the magnetization is visible, that is, produces an observable magnetic field signal. We refer to the remaining part of the magnetization as the hidden magnetization, and we recover it from a lithospheric magnetic field model under a few reasonable assumptions. We find that Earth's hidden magnetization at high and middle latitudes is very similar, both in intensity and shape, to Earth's visible magnetization. At low latitudes, the estimated hidden magnetization relies on a priori information and can be very different from the visible one. |
BibTeX:
@article{Vervelidou:2018,
author = {Vervelidou, F. and Lesur, V.},
title = {Unveiling Earth's hidden magnetisation},
journal = {Geophysical Research Letters},
year = {2018},
volume = {45},
number = {12},
pages = {283-292},
doi = {10.1029/2018GL079876}
}
|
| Coïsson P, Telali K, Heumez B, Lesur V, Lalanne X and Xin CJ (2017),
"Time-stamp correction of magnetic observatory data acquired during unavailability of time-synchronization services", Geoscientific Instrumentation, Methods and Data Systems. Vol. 6(2), pp. 311-317. |
| Abstract: During magnetic observatory data acquisition, the data time stamp is kept synchronized with a precise source of time. This is usually done using a GPS-controlled pulse per second (PPS) signal. For some observatories located in remote areas or where internet restrictions are enforced, only the magnetometer data are transmitted, limiting the capabilities of monitoring the acquisition operations. The magnetic observatory in Lanzhou (LZH), China, experienced an unnoticed interruption of the GPS PPS starting 7 March 2013. The data logger clock drifted slowly in time: in 6 months a lag of 27 s was accumulated. After a reboot on 2 April 2014 the drift became faster, −2 s per day, before the GPS PPS could be restored on 8 July 2014. To estimate the time lags that LZH time series had accumulated, we compared it with data from other observatories located in East Asia. A synchronization algorithm was developed. Natural sources providing synchronous events could be used as markers to obtain the time lag between the observatories. The analysis of slices of 1 h of 1 s data at arbitrary UTC allowed estimating time lags with an uncertainty of ∼ 11 s, revealing the correct trends of LZH time drift. A precise estimation of the time lag was obtained by comparing data from co-located instruments controlled by an independent PPS. In this case, it was possible to take advantage of spikes and local noise that constituted precise time markers. It was therefore possible to determine a correction to apply to LZH time stamps to correct the data files and produce reliable 1 min averaged definitive magnetic data. |
BibTeX:
@article{gi-6-311-2017,
author = {Coïsson, P. and Telali, K. and Heumez, B. and Lesur, V. and Lalanne, X. and Xin, C. J.},
title = {Time-stamp correction of magnetic observatory data acquired during unavailability of time-synchronization services},
journal = {Geoscientific Instrumentation, Methods and Data Systems},
year = {2017},
volume = {6},
number = {2},
pages = {311--317},
url = {https://www.geosci-instrum-method-data-syst.net/6/311/2017/},
doi = {10.5194/gi-6-311-2017}
}
|
| Lesur V, Heumez B, Telali A, Lalanne X and Soloviev A (2017),
"Estimating error statistics for Chambon-la-Forêt observatory definitive data", Annales Geophysicae. |
| Abstract: We propose a new algorithm for calibrating definitive observatory data with the goal of providing users with estimates of the data error standard deviations (SDs). The algorithm has been implemented and tested using Chambon-la-Forêt observatory (CLF) data. The calibration process uses all available data. It is set as a large, weakly non-linear, inverse problem that ultimately provides estimates of baseline values in three orthogonal directions, together with their expected standard deviations. For this inverse problem, absolute data error statistics are estimated from two series of absolute measurements made within a day. Similarly, variometer data error statistics are derived by comparing variometer data time series between different pairs of instruments over few years. The comparisons of these time series led us to use an autoregressive process of order 1 (AR1 process) as a prior for the baselines. Therefore the obtained baselines do not vary smoothly in time. They have relatively small SDs, well below 300 pT when absolute data are recorded twice a week – i.e. within the daily to weekly measures recommended by INTERMAGNET. The algorithm was tested against the process traditionally used to derive baselines at CLF observatory, suggesting that statistics are less favourable when this latter process is used. Finally, two sets of definitive data were calibrated using the new algorithm. Their comparison shows that the definitive data SDs are less than 400 pT and may be slightly overestimated by our process: an indication that more work is required to have proper estimates of absolute data error statistics. For magnetic field modelling, the results show that even on isolated sites like CLF observatory, there are very localised signals over a large span of temporal frequencies that can be as large as 1 nT. The SDs reported here encompass signals of a few hundred metres and less than a day wavelengths. |
BibTeX:
@article{Lesur:2017a,
author = {Lesur, V. and Heumez, B. and Telali, A. and Lalanne, X. and Soloviev, A.},
title = {Estimating error statistics for Chambon-la-Forêt observatory definitive data},
journal = {Annales Geophysicae},
year = {2017},
note = {in print},
doi = {10.5194/angeo-35-939-2017}
}
|
| Lesur V, Wardinski I, Baerenzung J and Holschneider M (2017),
"On the frequency spectra of the core magnetic field Gauss coefficients", Physics of the Earth and Planetary Interior. |
| Abstract: From monthly mean observatory data spanning 1957–2014, geomagnetic field secular variation values were calculated by annual differences. Estimates of the spherical harmonic Gauss coefficients of the core field secular variation were then derived by applying a correlation based modelling. Finally, a Fourier transform was applied to the time series of the Gauss coefficients. This process led to reliable temporal spectra of the Gauss coefficients up to spherical harmonic degree 5 or 6, and down to periods as short as 1 or 2 years depending on the coefficient. We observed that a k-2 slope, where k is the frequency, is an acceptable approximation for these spectra, with possibly an exception for the dipole field. The monthly estimates of the core field secular variation at the observatory sites also show that large and rapid variations of the latter happen. This is an indication that geomagnetic jerks are frequent phenomena and that significant secular variation signals at short time scales – i.e. less than 2 years, could still be extracted from data to reveal an unexplored part of the core dynamics. |
BibTeX:
@article{Lesur:2017b,
author = {Vincent Lesur and Ingo Wardinski and Julien Baerenzung and Matthias Holschneider},
title = {On the frequency spectra of the core magnetic field Gauss coefficients},
journal = {Physics of the Earth and Planetary Interior},
year = {2017},
doi = {10.1016/j.pepi.2017.05.017}
}
|
| Lukianova R, Uvarov V and Coïsson P (2017),
"High-latitude F region large-scale ionospheric irregularities under different solar wind and zenith angle conditions", Advances in Space Research. Vol. 59(2), pp. 557 - 570. |
| Abstract: A numerical model is used to study systematically the evolution of large scale irregularities depending on the IMF Bz and By components, solar zenith angle (seasonal and daily variation), solar and geomagnetic activity. The model enables to reproduce the 3-D distribution of electron density over the high-latitude F region ionosphere in the altitude range between 130 and 640 km. Since the convection electric field driven by changes in solar wind conditions has an important effect on the high-latitude ionosphere, the rotation of the IMF vector in the Y–Z plane causes a significant redistribution of the ionospheric plasma. Under the southward IMF conditions the plasma density is enhanced over a large portion of the near-pole ionosphere as a tongue of ionization, while the northward IMF leads to a considerable depletion and occurrence of the polar hole. The IMF By polarity is crucial for the shift and extension of the tongue of ionization to the dusk or dawn side. Particle precipitation also plays a role through a localized increase of the electron density mostly within the auroral oval and more pronounced auroral peak. The solar zenith angle, especially its seasonal variation, is the strongest regular factor influencing the electron density magnitude and spatial distribution. In winter, when the polar ionosphere is in darkness, large variations associated with different solar wind condition are more prominent. The daily variation of the zenith angle considerably modifies the Ne within a particular pattern. At a given time, the combined action of the IMF, solar zenith angle, level of solar and geomagnetic activity produces a complicated ionospheric response which can be considered as a superposition of different effects. Quantitative estimates of the ionospheric response to each factor are presented. |
BibTeX:
@article{Lukianova:2017,
author = {R.Yu. Lukianova and V.M. Uvarov and P. Coïsson},
title = {High-latitude F region large-scale ionospheric irregularities under different solar wind and zenith angle conditions},
journal = {Advances in Space Research},
year = {2017},
volume = {59},
number = {2},
pages = {557 - 570},
doi = {10.1016/j.asr.2016.10.010}
}
|
| Vervelidou F, Lesur V, Grott M, Morschhauser A and Lillis RJ (2017),
"Constraining the Date of the Martian Dynamo Shutdown by Means of Crater Magnetization Signatures", Journal of Geophysical Research: Planets., nov, 2017. Vol. 122(11), pp. 2294-2311. Wiley-Blackwell. |
| Abstract: Mars is believed to have possessed a dynamo that ceased operating approximately 4 Ga ago, although the exact time is still under debate. The scope of this study is to constrain the possible timing of its cessation by studying the magnetization signatures of craters. The study uses the latest available model of the lithospheric magnetic field of Mars, which is based on Mars Global Surveyor data. We tackle the problem of nonuniqueness that characterizes the inversion of magnetic field data for the magnetization by inferring only the visible part of the magnetization, that is, the part of the magnetization that gives rise to the observed magnetic field. Further on, we demonstrate that a zero visible magnetization is a valid proxy for the entire magnetization being zero under the assumption of a magnetization distribution of induced geometry. This assumption holds for craters whose thermoremanent magnetization has not been significantly altered since its acquisition. Our results show that the dynamo shut off after the impacts that created the Acidalia and SE Elysium basins and before the crust within the Utopia basin cooled below its magnetic blocking temperature. Accounting for the age uncertainties in the dating of these craters, we estimate that the dynamo shut off at an N(300) crater retention age of 2.5–3.2 or an absolute model age of 4.12–4.14 Ga. Moreover, the Martian dynamo may have been weaker in its early stage, which if true implies that the driving mechanism of the Martian dynamo was not the same throughout its history. |
BibTeX:
@article{Vervelidou2017b,
author = {Foteini Vervelidou and Vincent Lesur and Matthias Grott and Achim Morschhauser and Robert J. Lillis},
title = {Constraining the Date of the Martian Dynamo Shutdown by Means of Crater Magnetization Signatures},
journal = {Journal of Geophysical Research: Planets},
publisher = {Wiley-Blackwell},
year = {2017},
volume = {122},
number = {11},
pages = {2294--2311},
url = {https://doi.org/10.1002/2017je005410},
doi = {10.1002/2017je005410}
}
|
| Vervelidou F, Lesur V, Morschhauser A and Grott M (2017),
"On the accuracy of paleopole estimations from magnetic measurements", Geoph. J. Int.., Septembre, 2017. Vol. 211, pp. 1669-1678. |
| Abstract: Various techniques have been proposed for palaeopole position estimation based on magnetic field measurements. Such estimates can offer insights into the rotational dynamics and the dynamo history of moons and terrestrial planets carrying a crustal magnetic field. Motivated by discrepancies in the estimated palaeopole positions among various studies regarding the Moon and Mars, we examine the limitations of magnetic field measurements as source of information for palaeopole position studies. It is already known that magnetic field measurements cannot constrain the null space of the magnetization nor its full spectral content. However, the extent to which these limitations affect palaeopole estimates has not been previously investigated in a systematic way. In this study, by means of the vector Spherical Harmonics formalism, we show that inferring palaeopole positions from magnetic field measurements necessarily introduces, explicitly or implicitly, assumptions about both the null space and the full spectral content of the magnetization. Moreover, we demonstrate through synthetic tests that if these assumptions are inaccurate, then the resulting palaeopole position estimates are wrong. Based on this finding, we make suggestions that can allow future palaeopole studies to be conducted in a more constructive way. |
BibTeX:
@article{Vervelidou:2017,
author = {Vervelidou, F. and Lesur, V. and Morschhauser, A. and Grott, M.},
title = {On the accuracy of paleopole estimations from magnetic measurements},
journal = {Geoph. J. Int.},
year = {2017},
volume = {211},
pages = {1669--1678},
doi = {10.1093/gji/ggx400}
}
|
| Azzouzi I, Migoya-Orué YO, Coïsson P, Amory-Mazaudier C, Fleury R and Radicella SM (2016),
"Day-to-day variability of VTEC and ROTI in October 2012 with impact of high-speed solar wind stream on 13 October 2012", Sun and Geosphere. Vol. 11(1), pp. 2-22. |
| Abstract: This paper presents the day-to-day variability of the Vertical Total Electron Content (VTEC) and the Rate of change of TEC Index (ROTI) in October 2012. We focused our attention to the impact of a high-speed solar wind stream (HSSWS) on the ionosphere in middle and low latitudes on 13 October 2012. This event was preceded by two other disturbances caused by a Coronal Mass Ejection (CME) at 05:26UT on 8 October and a HSSWS around 19:00UT on 9 October. The changes in the VTEC observed during the period between 8 and 12 October preceding the 13 October case showed a comparable response of the ionosphere in both hemispheres, varying mainly with latitude and presenting a stronger impact in the Northern hemisphere. The VTEC increased at the arrival of the CME on 8 October, then decreased, and increased again on 13 October. The solar wind speed associated with the second HSSWS reached its peak, 580 km/s around 17:00UT during the recovery phase of a geomagnetic storm started around 00:00UT on 13 October. Its impact was observed in Africa and in Eastern South America on the ROTI, an indicator of ionospheric scintillation. On 13 October, the ROTI was small over whole Africa and in Eastern South America at the moment the impact of the second HSSWS. These observations are interpreted as due to the ionospheric disturbance dynamo electric field associated with the Joule heating produced in the auroral zone by the HSSWS. |
BibTeX:
@article{Azzouzi:2016,
author = {Azzouzi, I. and Migoya-Orué, Y. O. and Coïsson, P. and Amory-Mazaudier, C. and Fleury, R. and Radicella, S. M.},
title = {Day-to-day variability of VTEC and ROTI in October 2012 with impact of high-speed solar wind stream on 13 October 2012},
journal = {Sun and Geosphere},
year = {2016},
volume = {11},
number = {1},
pages = {2-22},
url = {http://newserver.stil.bas.bg/SUNGEO//sun_geo_content.html#v111}
}
|
| Baerenzung J, Holschneider M and Lesur V (2016),
"The flow at the Earth's core mantle boundary under weak prior constraints", Journal of Geophysical Research (Solid Earth). Vol. 121(3), pp. 1343-1364. |
| Abstract: Prior information in ill-posed inverse problem is of critical importance because it is conditioning the posterior solution and its associated variability. The problem of determining the flow evolving at the Earth's core-mantle boundary through magnetic field models derived from satellite or observatory data is no exception to the rule. This study aims to estimate what information can be extracted on the velocity field at the core-mantle boundary, when the frozen flux equation is inverted under very weakly informative, but realistic, prior constraints. Instead of imposing a converging spectrum to the flow, we simply assume that its poloidal and toroidal energy spectra are characterized by power laws. The parameters of the spectra, namely, their magnitudes, and slopes are unknown. The connection between the velocity field, its spectra parameters, and the magnetic field model is established through the Bayesian formulation of the problem. Working in two steps, we determined the time-averaged spectra of the flow within the 2001–2009.5 period, as well as the flow itself and its associated uncertainties in 2005.0. According to the spectra we obtained, we can conclude that the large-scale approximation of the velocity field is not an appropriate assumption within the time window we considered. For the flow itself, we show that although it is dominated by its equatorial symmetric component, it is very unlikely to be perfectly symmetric. We also demonstrate that its geostrophic state is questioned in different locations of the outer core. |
BibTeX:
@article{Baerenzung:2016,
author = {Baerenzung, J. and Holschneider, M. and Lesur, V.},
title = {The flow at the Earth's core mantle boundary under weak prior constraints},
journal = {Journal of Geophysical Research (Solid Earth)},
year = {2016},
volume = {121},
number = {3},
pages = {1343-1364},
doi = {10.1002/2015JB012464}
}
|
| Catalán M, Dyment J, Lesur V, Thébault E, Hamoudi M, Choi Y, Santis AD, Takemi I, Korhonen J, Litvinova T, Luís J, Meyer B, Milligan P, Masao N, Okuma S, Pilkington M, Purucker M, Ravat D, Gaina C, Maus S, Quesnel Y, Saltus R and Taylor P (2016),
"Making a better magnetic map", Eos. Vol. 97 |
| Abstract: A new version of the World Digital Magnetic Anomaly Map, released last summer, gives greater insight into the structure and history of Earth's crust and upper mantle. |
BibTeX:
@article{Catalan:2016,
author = {Manuel Catalán and Jérôme Dyment and Vincent Lesur and Erwan Thébault and Mohamed Hamoudi and Yujin Choi and Angelo De Santis and Ishihara Takemi and Juha Korhonen and Tamara Litvinova and Joaquim Luís and Brian Meyer and Peter Milligan and Nakanishi Masao and Shigeo Okuma and Mark Pilkington and Michael Purucker and Dhananjay Ravat and Carmen Gaina and Stefan Maus and Yoann Quesnel and Richard Saltus and Patrick Taylor},
title = {Making a better magnetic map},
journal = {Eos},
year = {2016},
volume = {97},
doi = {10.1029/2016EO054645}
}
|
| Finlay CC, Lesur V, Thébault E, Vervelidou F, Morschhauser A and Shore R (2016),
"Challenges handling magnetospheric and ionospheric signals in internal geomagnetic field modelling", Space Science Reviews. |
| Abstract: Measurements of the Earth’s magnetic field collected by low-Earth-orbit satellites such as Swarm and CHAMP, as well as at ground observatories, are dominated by sources in the Earth’s interior. However these measurements also contain significant contributions from more rapidly-varying current systems in the ionosphere and magnetosphere. In order to fully exploit magnetic data to probe the physical properties and dynamics of the Earth’s interior, field models with suitable treatments of external sources, and their associated induced signals, are essential. Here we review the methods presently used to construct models of the internal field, focusing on techniques to handle magnetospheric and ionospheric signals. Shortcomings of these techniques often limit the quality, as well as spatial and temporal resolution, of internal field models. We document difficulties in using track-by-track analysis to characterize magnetospheric field fluctuations, differences in internal field models that result from alternative treatments of the quiet-time ionospheric field, and challenges associated with rapidly changing, but spatially correlated, magnetic signatures of polar cap current systems. Possible strategies for improving internal field models are discussed, many of which are described in more detail elsewhere in this volume. |
BibTeX:
@article{Finlay:2016,
author = {Finlay, C. C. and Lesur, V. and Thébault, E. and Vervelidou, F. and Morschhauser, A. and Shore, R.},
title = {Challenges handling magnetospheric and ionospheric signals in internal geomagnetic field modelling},
journal = {Space Science Reviews},
year = {2016},
doi = {10.1007/s11214-016-0285-9}
}
|
| Holschneider M, Lesur V, Mauerberger S and Baerenzung J (2016),
"Correlation based modelling and separation of geomagnetic field components", J. Geophys. Res. Solid Earth. Vol. 121, pp. 3142-3160. |
| Abstract: We introduce a technique for the modeling and separation of geomagnetic field components that is based on an analysis of their correlation structures alone. The inversion is based on a Bayesian formulation, which allows the computation of uncertainties. The technique allows the incorporation of complex measurement geometries like observatory data in a simple way. We show how our technique is linked to other well-known inversion techniques. A case study based on observational data is given. |
BibTeX:
@article{Holschneider:2016,
author = {Holschneider, M. and Lesur, V. and Mauerberger, S. and Baerenzung, J.},
title = {Correlation based modelling and separation of geomagnetic field components},
journal = {J. Geophys. Res. Solid Earth},
year = {2016},
volume = {121},
pages = {3142-3160},
doi = {10.1002/2015JB012629}
}
|
| Larnier H, Sailhac P and Chambodut A (2016),
"New application of wavelets in magnetotelluric data processing: reducing impedance bias", Earth, Planets and Space. Vol. 68(1) Springer Nature. |
| Abstract: Magnetotelluric (MT) data consist of the sum of several types of natural sources including transient and quasiperiodic signals and noise sources (instrumental, anthropogenic) whose nature has to be taken into account in MT data processing. Most processing techniques are based on a Fourier transform of MT time series, and robust statistics at a fixed frequency are used to compute the MT response functions, but only a few take into account the nature of the sources. Moreover, to reduce the influence of noise in the inversion of the response functions, one often sets up another MT station called a remote station. However, even careful setup of this remote station cannot prevent its failure in some cases. Here, we propose the use of the continuous wavelet transform on magnetotelluric time series to reduce the influence of noise even for single site processing. We use two different types of wavelets, Cauchy and Morlet, according to the shape of observed geomagnetic events. We show that by using wavelet coefficients at clearly identified geomagnetic events, we are able to recover the unbiased response function obtained through robust remote processing algorithms. This makes it possible to process even single station sites and increase the confidence in data interpretation. |
BibTeX:
@article{Larnier2016,
author = {Hugo Larnier and Pascal Sailhac and Aude Chambodut},
title = {New application of wavelets in magnetotelluric data processing: reducing impedance bias},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2016},
volume = {68},
number = {1},
url = {https://doi.org/10.1186/Fs40623-016-0446-9},
doi = {10.1186/s40623-016-0446-9}
}
|
| Lesur V, Hamoudi M, Choi Y, Dyment J and Thébault E (2016),
"Building the second version of the World Digital Magnetic Anomaly Map (WDMAM)", Earth, Planets and Space. |
| Abstract: The World Digital Anomaly Map (WDMAM) is a worldwide compilation of near-surface magnetic data. We present here a candidate for the second version of the WDMAM and its characteristics. This candidate has been evaluated by a group of independent reviewers and has been adopted as the official second version of the WDMAM during the 26th general assembly of the International Union of Geodesy and Geomagnetism (IUGG). The way this compilation has been built is described with some details. A global magnetic field model of the lithosphere contribution, parameterised by spherical harmonics, has been derived up to degree and order 800. The model information content has been evaluated by computing local spectra. Further, the compatibility of the anomaly field displayed by the WDMAM with a pure induced magnetisation is tested by comparison with the main field strength. These studies allowed an analysis of the compilation in terms of strength and wavelength content. They confirm the extremely smooth and weak contribution of the magnetic field generated in the lithosphere over Western Europe. This apparent weakness possibly extends to the Northern African continent. However, a global analysis remains difficult to achieve given the sparseness of good quality data over very large area of oceans and continents. The WDMAM and related information can be downloaded at http://www.wdmam.org/. |
BibTeX:
@article{Lesur:2016,
author = {Lesur, V. and Hamoudi, M. and Choi, Y. and Dyment, J. and Thébault, E.},
title = {Building the second version of the World Digital Magnetic Anomaly Map (WDMAM)},
journal = {Earth, Planets and Space},
year = {2016},
doi = {10.1186/s40623-016-0404-6}
}
|
| Love J and Coïsson P (2016),
"The geomagnetic blitz of September 1941", Eos. Vol. 97 |
| Abstract: Seventy-five years ago, on 18–19 September 1941, the Earth experienced a great magnetic storm, one of the most intense ever recorded. It arrived at a poignant moment in history, when radio and electrical technology was emerging as a central part of daily life and when much of the world was embroiled in World War II, which the United States had not yet officially entered. Auroras danced across the night sky as voltage surged in power grid lines. A radio blackout interrupted fan enjoyment of a baseball game, while another radio program was interrupted by private phone conversations. Citizens, already on edge, wondered if neon lights were some sort of antiaircraft signal. And far away in the North Atlantic, the illuminated night sky exposed an Allied convoy to German attack. These effects raised awareness within the scientific community and among the public of the societal significance of the effects that the Sun and outer space can have on the Earth—what we now call space weather. |
BibTeX:
@article{Love:2016b,
author = {Love, J. and Coïsson, P.},
title = {The geomagnetic blitz of September 1941},
journal = {Eos},
year = {2016},
volume = {97},
doi = {10.1029/2016EO059319}
}
|
| Love J, Coïsson P and Pulkkinen A (2016),
"Global statistical maps of extreme-event magnetic observatory 1 min first differences in horizontal intensity", Geophysical Research Letters. Vol. 43 |
| Abstract: Analysis is made of the long-term statistics of three different measures of ground level, storm time geomagnetic activity: instantaneous 1 min first differences in horizontal intensity ΔBh, the root-mean-square of 10 consecutive 1 min differences S, and the ramp change R over 10 min. Geomagnetic latitude maps of the cumulative exceedances of these three quantities are constructed, giving the threshold (nT/min) for which activity within a 24 h period can be expected to occur once per year, decade, and century. Specifically, at geomagnetic 55,^circ, we estimate once-per-century ΔBh, S, and R exceedances and a site-to-site, proportional, 1 standard deviation range [1 σ, lower and upper] to be, respectively, 1000, [690, 1450]; 500, [350, 720]; and 200, [140, 280] nT/min. At 40,^circ, we estimate once-per-century ΔBh, S, and R exceedances and 1 σ values to be 200, [140, 290]; 100, [70, 140]; and 40, [30, 60] nT/min. |
BibTeX:
@article{Love:2016,
author = {Love, J.J. and Coïsson, P. and Pulkkinen, A.},
title = {Global statistical maps of extreme-event magnetic observatory 1 min first differences in horizontal intensity},
journal = {Geophysical Research Letters},
year = {2016},
volume = {43},
url = {http://dx.doi.org/10.1002/2016GL068664},
doi = {10.1002/2016GL068664}
}
|
| Migoya Orué Y, Azzouzi I, Coïsson P, Amory-Mazaudier C, Fleury R and Radicella SM (2016),
"Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012", Sun and Geosphere. Vol. 11(1), pp. 23-35. |
| Abstract: This paper presents the impact of a fast solar wind on the ionosphere, in low latitudes, on 13 October 2012. On that day, the high speed solar wind reached the Earth around 16:00UT, during the recovery phase of a geomagnetic storm which started around 00:00UT. The solar wind speed was determined to be 580km/s, on the same day, around 17:00UT. Its impact was observed in low and equatorial latitudes, in Africa and in Eastern South America, on the F layer and on the geomagnetic field variations. Through the analysis of magnetic indices, ionosonde characteristics and the horizontal component of the geomagnetic field, we found that the 13 October 2012 event exhibited a local impact, affecting the observatories situated in a longitude sector between 315°E and 45°E. Particularly, the F layer in Afica (observed by the ionosonde at Ascension Island) did not present any lift, and there was a delay for approximately two hours of the ascent of the F layer in America (the ionosonde at Fortaleza). In this case, there was an evident inhibition on the development of spread F at the time of the Pre Reversal Enhancement (PRE) in Africa and Eastern America, while the ionograms of the days before and after presented clear spread F traces. The disturbances of the ionospheric equivalent electric current (Diono) deduced from the variations of the geomagnetic field at M'Bour near Daka (Africa) and at Kourou (Eastern America) exhibited on the dayside, an anti Sq current which is signature of the influence of the Disturbance Dynamo Electric Field (DDEF). |
BibTeX:
@article{MigoyaOrue:2016,
author = {Migoya Orué, Y.O. and Azzouzi, I. and Coïsson, P. and Amory-Mazaudier, C. and Fleury, R. and Radicella, S. M.},
title = {Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012},
journal = {Sun and Geosphere},
year = {2016},
volume = {11},
number = {1},
pages = {23-35},
url = {http://newserver.stil.bas.bg/SUNGEO//sun_geo_content.html#v111}
}
|
| Thébault E, Lesur V, Kauristie K and Shore R (2016),
"Magnetic Field Data Correction in Space for Modelling the Lithospheric Magnetic Field", Space Science Reviews. , pp. 1-33. |
| Abstract: The Earth's magnetic field as it is measured by low-Earth orbit satellites such as Swarm and CHAMP results from the superposition of internal and external source fields overlapping in time and in space. The Earth's lithospheric field is one of the weakest sources detectable from space and its accurate description requires treatments of rapidly-varying magnetic fields generated by current systems in the ionosphere and magnetosphere. In this paper, we review methods most commonly used in geomagnetism to identify and then to correct for the external perturbation fields at satellite altitudes. We document the pros and cons of Fourier Filtering, polynomial and Spherical Harmonics analyses, Singular Spectral Analysis (SSA) and Line-levelling techniques. The difficulties are illustrated with an application of the methods on a common set of real Swarm magnetic field measurements and with a discussion on the differences between lithospheric field models obtained with each treatment. We finally discuss some perspectives for improvements of external field correction techniques relying on statistical or more explicit assumptions about the geographical distribution as well as the shape and strengths of the external magnetic field structures. |
BibTeX:
@article{Thebault:2016,
author = {Thébault, E. and Lesur, V. and Kauristie, K. and Shore, R.},
title = {Magnetic Field Data Correction in Space for Modelling the Lithospheric Magnetic Field},
journal = {Space Science Reviews},
year = {2016},
pages = {1--33},
url = {http://dx.doi.org/10.1007/s11214-016-0309-5},
doi = {10.1007/s11214-016-0309-5}
}
|
| Tøffner-Clausen L, Lesur V, Olsen N and Finlay C (2016),
"In-flight Scalar Calibration and Characterisation of the Swarm Magnetometry Package", Earth Planets and Space. , pp. 68:129. |
| Abstract: We present the in-flight scalar calibration and characterisation of the Swarm magnetometry package consisting of the absolute scalar magnetometer, the vector magnetometer, and the spacecraft structure supporting the instruments. A significant improvement in the scalar residuals between the pairs of magnetometers is demonstrated, confirming the high performance of these instruments. The results presented here, including the characterisation of a Sun-driven disturbance field, form the basis of the correction of the magnetic vector measurements from Swarm which is applied to the Swarm Level 1b magnetic data. |
BibTeX:
@article{Toffner-Clausen:2016,
author = {Tøffner-Clausen, L. and Lesur, V. and Olsen, N. and Finlay, C.},
title = {In-flight Scalar Calibration and Characterisation of the Swarm Magnetometry Package},
journal = {Earth Planets and Space},
year = {2016},
pages = {68:129},
doi = {10.1186/s40623-016-0501-6}
}
|
| Di Mauro D, Cafarella L, Lepidi S, Pietrolungo M, Alfonsi L and Chambodut A (2015),
"Geomagnetic polar observatories: the role of Concordia station at Dome C, Antarctica", Annals of Geophysics. Vol. 57(6) Istituto Nazionale di Geofisica e Vulcanologia, INGV. |
| Abstract: A geomagnetic observatory is a permanent facility where magnetic declination and inclination are recorded in conjunction with the temporal evolution of the magnetic field components. Polar regions are scarcely covered by observational points then the contributions from observatories located there are particularly relevant. The geomagnetic observatory at Concordia station, Dome C - Antarctica is located in the inner part of the continent, its position is favorable for two key reasons, i) data are unaltered by the "coastal effect” and ii) crustal effect is negligible due to the thickness, almost 3 km, of ice coverage. Nevertheless, these latter conditions imply an unconsidered aspect which characterizes the entire station and every structure laying on the ice surface: the dome on which Concordia station resides is sliding horizontally and moving vertically with a velocity of few millimeter to centimeters per year as indicated by independent geodetic observations. This slow and continuous movement has a puzzling effect on the trend of horizontal components of the magnetic field, sampled in a time window of a decade since the establishing of the observatory in 2005. During the International Polar Year (2007-2009) the observatory was upgraded with new equipment fulfilling the requirements of the Intermagnet consortium, and becoming an observatory member in 2011. In this paper are illustrated the strategy adopted to track any possible displacement of the observatory reference points (i.e. the azimuth mark, the pillar position) and all the ordinary and extraordinary actions required for collecting high quality data. |
BibTeX:
@article{DiMauro2015,
author = {Di Mauro, Domenico and Cafarella, Lili and Lepidi, Stefania and Pietrolungo, Manuela and Alfonsi, Laura and Chambodut, Aude},
title = {Geomagnetic polar observatories: the role of Concordia station at Dome C, Antarctica},
journal = {Annals of Geophysics},
publisher = {Istituto Nazionale di Geofisica e Vulcanologia, INGV},
year = {2015},
volume = {57},
number = {6},
url = {http://doi.org/10.4401/ag-6605},
doi = {10.4401/ag-6605}
}
|
| Du J, Chen C, Lesur V, Lane R and Wang H (2015),
"Magnetic potential, vector and gradient tensor fields of a tesseroid in a geocentric spherical coordinate system", Geophys J. Int.. Vol. 201(3), pp. 1977-2007. |
| Abstract: We examined the mathematical and computational aspects of the magnetic potential, vector and gradient tensor fields of a tesseroid in a geocentric spherical coordinate system (SCS). This work is relevant for 3-D modelling that is performed with lithospheric vertical scales and global, continent or large regional horizontal scales. The curvature of the Earth is significant at these scales and hence, a SCS is more appropriate than the usual Cartesian coordinate system (CCS). The 3-D arrays of spherical prisms (SP; ‘tesseroids’) can be used to model the response of volumes with variable magnetic properties. Analytical solutions do not exist for these model elements and numerical or mixed numerical and analytical solutions must be employed. We compared various methods for calculating the response in terms of accuracy and computational efficiency. The methods were (1) the spherical coordinate magnetic dipole method (MD), (2) variants of the 3-D Gauss–Legendre quadrature integration method (3-D GLQI) with (i) different numbers of nodes in each of the three directions, and (ii) models where we subdivided each SP into a number of smaller tesseroid volume elements, (3) a procedure that we term revised Gauss–Legendre quadrature integration (3-D RGLQI) where the magnetization direction which is constant in a SCS is assumed to be constant in a CCS and equal to the direction at the geometric centre of each tesseroid, (4) the Taylor's series expansion method (TSE) and (5) the rectangular prism method (RP). In any realistic application, both the accuracy and the computational efficiency factors must be considered to determine the optimum approach to employ. In all instances, accuracy improves with increasing distance from the source. It is higher in the percentage terms for potential than the vector or tensor response. The tensor errors are the largest, but they decrease more quickly with distance from the source. In our comparisons of relative computational efficiency, we found that the magnetic potential takes less time to compute than the vector response, which in turn takes less time to compute than the tensor gradient response. The MD method takes less time to compute than either the TSE or RP methods. The efficiency of the (GLQI and) RGLQI methods depends on the polynomial order, but the response typically takes longer to compute than it does for the other methods. The optimum method is a complex function of the desired accuracy, the size of the volume elements, the element latitude and the distance between the source and the observation. For a model of global extent with typical model element size (e.g. 1 degree horizontally and 10 km radially) and observations at altitudes of 10s to 100s of km, a mixture of methods based on the horizontal separation of the source and observation separation would be the optimum approach. To demonstrate the RGLQI method described within this paper, we applied it to the computation of the response for a global magnetization model for observations at 300 and 30 km altitude. |
BibTeX:
@article{Du:2015,
author = {Jinsong Du and Chao Chen and Vincent Lesur and Richard Lane and Huilin Wang},
title = {Magnetic potential, vector and gradient tensor fields of a tesseroid in a geocentric spherical coordinate system},
journal = {Geophys J. Int.},
year = {2015},
volume = {201},
number = {3},
pages = {1977-2007},
doi = {10.1093/gji/ggv123}
}
|
| Dyment J, Choi Y, Hamoudi M, Lesur V and Thébault E (2015),
"Global equivalent magnetization of the oceanic lithosphere", Earth and Planetary Science Letters. Vol. 430, pp. 54-65. |
| Abstract: As a by-product of the construction of a new World Digital Magnetic Anomaly Map over oceanic areas, we use an original approach based on the global forward modeling of seafloor spreading magnetic anomalies and their comparison to the available marine magnetic data to derive the first map of the equivalent magnetization over the World's ocean. This map reveals consistent patterns related to the age of the oceanic lithosphere, the spreading rate at which it was formed, and the presence of mantle thermal anomalies which affects seafloor spreading and the resulting lithosphere. As for the age, the equivalent magnetization decreases significantly during the first 10–15 Myr after its formation, probably due to the alteration of crustal magnetic minerals under pervasive hydrothermal alteration, then increases regularly between 20 and 70 Ma, reflecting variations in the field strength or source effects such as the acquisition of a secondary magnetization. As for the spreading rate, the equivalent magnetization is twice as strong in areas formed at fast rate than in those formed at slow rate, with a threshold at ∼40 km/Myr, in agreement with an independent global analysis of the amplitude of Anomaly 25. This result, combined with those from the study of the anomalous skewness of marine magnetic anomalies, allows building a unified model for the magnetic structure of normal oceanic lithosphere as a function of spreading rate. Finally, specific areas affected by thermal mantle anomalies at the time of their formation exhibit peculiar equivalent magnetization signatures, such as the cold Australian–Antarctic Discordance, marked by a lower magnetization, and several hotspots, marked by a high magnetization. |
BibTeX:
@article{Dyment:2015,
author = {J. Dyment and Y. Choi and M. Hamoudi and V. Lesur and E. Thébault},
title = {Global equivalent magnetization of the oceanic lithosphere},
journal = {Earth and Planetary Science Letters},
year = {2015},
volume = {430},
pages = {54-65},
doi = {10.1016/j.epsl.2015.08.002}
}
|
| Léger J-M, Jager T, Bertrand F, Hulot G, Brocco L, Vigneron P, Lalanne X, Chulliat A and Fratter I (2015),
"In-flight performance of the Absolute Scalar Magnetometer vector mode on board the Swarm satellites", Earth, Planets and Space. Vol. 67(1), pp. 57. |
| Abstract: The role of the Absolute Scalar Magnetometer (ASM) in the European Space Agency (ESA) Swarm mission is to deliver absolute measurements of the magnetic field's strength for science investigations and in-flight calibration of the Vector Field Magnetometer (VFM). However, the ASM instrument can also simultaneously deliver vector measurements with no impact on the magnetometer's scalar performance, using a so-called vector mode. This vector mode has been continuously operated since the beginning of the mission, except for short periods of time during commissioning. Since both scalar and vector measurements are perfectly synchronous and spatially coherent, a direct assessment of the ASM vector performance can then be carried out at instrument level without need to correct for the various magnetic perturbations generated by the satellites. After a brief description of the instrument's operating principles, a thorough analysis of the instrument's behavior is presented, as well as a characterization of its environment in flight, using an alternative high sampling rate (burst) scalar mode that could be run a few days during commissioning. The ASM vector calibration process is next detailed, with some emphasis on its sensitivity to operational conditions. Finally, the evolution of the instrument's performance during the first year of the mission is presented and discussed in view of the mission's performance requirements for vector measurements. |
BibTeX:
@article{Leger:2015,
author = {Léger, Jean-Michel and Jager, Thomas and Bertrand, François and Hulot, Gauthier and Brocco, Laura and Vigneron, Pierre and Lalanne, Xavier and Chulliat, Arnaud and Fratter, Isabelle},
title = {In-flight performance of the Absolute Scalar Magnetometer vector mode on board the Swarm satellites},
journal = {Earth, Planets and Space},
year = {2015},
volume = {67},
number = {1},
pages = {57},
doi = {10.1186/s40623-015-0231-1}
}
|
| Lesur V, Rother M, Wardinski I, Schachtschneider R, Hamoudi M and Chambodut A (2015),
"Parent magnetic field models for the IGRF-12 GFZ-candidates", Earth, Planets and Space. Vol. 67(87) |
| Abstract: We propose candidate models for IGRF-12. These models were derived from parent models built from 10 months of Swarm satellite data and 1.5 years of magnetic observatory data. Using the same parameterisation, a magnetic field model was built from a slightly extended satellite data set. As a result of discrepancies between magnetic field intensity measured by the absolute scalar instrument and that calculated from the vector instrument, we re-calibrated the satellite data. For the calibration, we assumed that the discrepancies resulted from a small perturbing magnetic field carried by the satellite, with a strength and orientation dependent on the Sun’s position relative to the satellite. Scalar and vector data were reconciled using only a limited number of calibration parameters. The data selection process, followed by the joint modelling of the magnetic field and Euler angles, leads to accurate models of the main field and its secular variation around 2014.0. The obtained secular variation model is compared with models based on CHAMP satellite data. The comparison suggests that pulses of magnetic field acceleration that were observed on short time scales average-out over a decade. |
BibTeX:
@article{Lesur:2015,
author = {Vincent Lesur and Martin Rother and Ingo Wardinski and Reyko Schachtschneider and Mohamed Hamoudi and Aude Chambodut},
title = {Parent magnetic field models for the IGRF-12 GFZ-candidates},
journal = {Earth, Planets and Space},
year = {2015},
volume = {67},
number = {87},
doi = {10.1186/s40623-015-0239-6}
}
|
| Lesur V, Whaler K and Wardinski I (2015),
"Are geomagnetic data consistent with stably stratified flow at the core-mantle boundary?", Geophys. J. Int.. Vol. 201(2), pp. 929 - 946. |
| Abstract: Recent first principles calculations of the Earth's outer core thermal and electrical conductivities have raised their values by a factor of three. This has significant implications for geodynamo operation, in particular, forcing the development of a stably stratified layer at the core–mantle boundary (CMB). This study seeks to test the hypothesis of a stably stratified layer in the uppermost core by analysing geomagnetic observations made by the CHAMP satellite. An inversion method is utilized that jointly solves for the time-dependent main field and the core surface flow, where we assume the temporal variability of the main field, its secular variation (SV), to be entirely due to advective motion within the liquid outer core. The results show that a large-scale pure toroidal flow, consistent with a stably stratified layer atop the outer core, is not compatible with the observed magnetic field during the CHAMP era. However, allowing just a small amount of poloidal flow leads to a model fitting the observations satisfactorily. As this poloidal flow component is large scale, within a predominantly toroidal, essentially tangentially geostrophic flow, it is compatible with a stably stratified upper outer core. Further, our assumption of little or no diffusive SV may not hold, and a small amount of SV generated locally by diffusion might lead to a large-scale pure toroidal flow providing an acceptable fit to the data. |
BibTeX:
@article{Lesur:2014,
author = {Lesur, V. and Whaler, K. and Wardinski, I.},
title = {Are geomagnetic data consistent with stably stratified flow at the core-mantle boundary?},
journal = {Geophys. J. Int.},
year = {2015},
volume = {201},
number = {2},
pages = {929 -- 946},
doi = {10.1093/gji/ggv031}
}
|
| Olsen N, Hulot G, Lesur V, Finlay C, Beggan C, Chulliat A, Sabaka T, Floberghagen R, Friis-Christensen E, Haagmans R, Kotsiaros S, Lühr H, Tøffner-Clausen L and Vigneron P (2015),
"The Swarm Initial Field Model for the 2014 geomagnetic field", Geophys. Res. Lett.. Vol. 42 |
| Abstract: Data from the first year of ESA's Swarm constellation mission are used to derive the Swarm Initial Field Model (SIFM), a new model of the Earth's magnetic field and its time variation. In addition to the conventional magnetic field observations provided by each of the three Swarm satellites, explicit advantage is taken of the constellation aspect by including east-west magnetic intensity gradient information from the lower satellite pair. Along-track differences in magnetic intensity provide further information concerning the north-south gradient. The SIFM static field shows excellent agreement (up to at least degree 60) with recent field models derived from CHAMP data, providing an initial validation of the quality of the Swarm magnetic measurements. Use of gradient data improves the determination of both the static field and its secular variation, with the mean misfit for east-west intensity differences between the lower satellite pair being only 0.12 nT. |
BibTeX:
@article{Olsen:2015,
author = {Nils Olsen and Gauthier Hulot and Vincent Lesur and Christopher Finlay and Ciaran Beggan and Arnaud Chulliat and Terence Sabaka and Rune Floberghagen and Eigil Friis-Christensen and Roger Haagmans and Stavros Kotsiaros and Hermann Lühr and Lars Tøffner-Clausen and Pierre Vigneron},
title = {The Swarm Initial Field Model for the 2014 geomagnetic field},
journal = {Geophys. Res. Lett.},
year = {2015},
volume = {42},
doi = {10.1002/2014GL062659}
}
|
| Thébault E, Finlay C, Alken P, Beggan C, Canet E, Chulliat A, Langlais B, Lesur V, Lowes F, Manoj C, Rother M and Schachtschneider R (2015),
"Evaluation of candidate geomagnetic field models for IGRF-12", Earth, Planets, and Space. Vol. 67(112) |
| Abstract: Background The 12th revision of the International Geomagnetic Reference Field (IGRF) was issued in December 2014 by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD (http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html). This revision comprises new spherical harmonic main field models for epochs 2010.0 (DGRF-2010) and 2015.0 (IGRF-2015) and predictive linear secular variation for the interval 2015.0-2020.0 (SV-2010-2015). Findings Conclusions |
BibTeX:
@article{Thebault:2015b,
author = {E. Thébault and C.C. Finlay and P. Alken and C.D. Beggan and E. Canet and A. Chulliat and B. Langlais and V. Lesur and F.J. Lowes and C. Manoj and M. Rother and R. Schachtschneider},
title = {Evaluation of candidate geomagnetic field models for IGRF-12},
journal = {Earth, Planets, and Space},
year = {2015},
volume = {67},
number = {112},
doi = {10.1186/s40623-015-0273-4}
}
|
| Thébault E, Finlay CC, Beggan CD, Alken P, Aubert J, Barrois O, Bertrand F, Bondar T, Boness A, Brocco L, Canet E, Chambodut A, Chulliat A, Coïsson P, Civet F, Du A, Fournier A, Fratter I, Gillet N, Hamilton B, Hamoudi M, Hulot G, Jager T, Korte M, Kuang W, Lalanne X, Langlais B, Léger J-M, Lesur V, Lowes FJ, Macmillan S, Mandea M, Manoj C, Maus S, Olsen N, Petrov V, Ridley V, Rother M, Sabaka TJ, Saturnino D, Schachtschneider R, Sirol O, Tangborn A, Thomson A, Tøffner-Clausen L, Vigneron P, Wardinski I and Zvereva T (2015),
"International Geomagnetic Reference Field: the 12th generation", Earth, Planets and Space. Vol. 67(1), pp. 79. |
| Abstract: The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth's magnetic field. |
BibTeX:
@article{Thebault:2015,
author = {Thébault, Erwan and Finlay, Christopher C. and Beggan, Ciarán D. and Alken, Patrick and Aubert, Julien and Barrois, Olivier and Bertrand, Francois and Bondar, Tatiana and Boness, Axel and Brocco, Laura and Canet, Elisabeth and Chambodut, Aude and Chulliat, Arnaud and Coïsson, Pierdavide and Civet, François and Du, Aimin and Fournier, Alexandre and Fratter, Isabelle and Gillet, Nicolas and Hamilton, Brian and Hamoudi, Mohamed and Hulot, Gauthier and Jager, Thomas and Korte, Monika and Kuang, Weijia and Lalanne, Xavier and Langlais, Benoit and Léger, Jean-Michel and Lesur, Vincent and Lowes, Frank J. and Macmillan, Susan and Mandea, Mioara and Manoj, Chandrasekharan and Maus, Stefan and Olsen, Nils and Petrov, Valeriy and Ridley, Victoria and Rother, Martin and Sabaka, Terence J. and Saturnino, Diana and Schachtschneider, Reyko and Sirol, Olivier and Tangborn, Andrew and Thomson, Alan and Tøffner-Clausen, Lars and Vigneron, Pierre and Wardinski, Ingo and Zvereva, Tatiana},
title = {International Geomagnetic Reference Field: the 12th generation},
journal = {Earth, Planets and Space},
year = {2015},
volume = {67},
number = {1},
pages = {79},
doi = {10.1186/s40623-015-0228-9}
}
|
| Vigneron P, Hulot G, Olsen N, Leger J-M, Jager T, Brocco L, Sirol O, Coïsson P, Lalanne X, Chulliat A, Bertrand F, Boness A and Fratter I (2015),
"A 2015 International Geomagnetic Reference Field (IGRF) candidate model based on Swarm's experimental absolute magnetometer vector mode data", Earth, Planets and Space. Vol. 67(1), pp. 95. |
| Abstract: Each of the three satellites of the European Space Agency Swarm mission carries an absolute scalar magnetometer (ASM) that provides the nominal 1-Hz scalar data of the mission for both science and calibration purposes. These ASM instruments, however, also deliver autonomous 1-Hz experimental vector data. Here, we report on how ASM-only scalar and vector data from the Alpha and Bravo satellites between November 29, 2013 (a week after launch) and September 25, 2014 (for on-time delivery of the model on October 1, 2014) could be used to build a very valuable candidate model for the 2015.0 International Geomagnetic Reference Field (IGRF). A parent model was first computed, describing the geomagnetic field of internal origin up to degree and order 40 in a spherical harmonic representation and including a constant secular variation up to degree and order 8. This model was next simply forwarded to epoch 2015.0 and truncated at degree and order 13. The resulting ASM-only 2015.0 IGRF candidate model is compared to analogous models derived from the mission’s nominal data and to the now-published final 2015.0 IGRF model. Differences among models mainly highlight uncertainties enhanced by the limited geographical distribution of the selected data set (essentially due to a lack of availability of data at high northern latitude satisfying nighttime conditions at the end of the time period considered). These appear to be comparable to differences classically observed among IGRF candidate models. These positive results led the ASM-only 2015.0 IGRF candidate model to contribute to the construction of the final 2015.0 IGRF model. |
BibTeX:
@article{Vigneron:2015,
author = {Vigneron, P. and Hulot, G. and Olsen, N. and Leger, J.-M. and Jager, T. and Brocco, L. and Sirol, O. and Coïsson, P. and Lalanne, X. and Chulliat, A. and Bertrand, F. and Boness, A. and Fratter, I.},
title = {A 2015 International Geomagnetic Reference Field (IGRF) candidate model based on Swarm's experimental absolute magnetometer vector mode data},
journal = {Earth, Planets and Space},
year = {2015},
volume = {67},
number = {1},
pages = {95},
doi = {10.1186/s40623-015-0265-4}
}
|
| Alken P, Chulliat A and Maus S (2013),
"Longitudinal and seasonal structure of the ionospheric equatorial electric field", Journal of Geophysical Research: Space Physics. Vol. 118(3), pp. 1298-1305. Wiley-Blackwell. |
| Abstract: The daytime eastward equatorial electric field (EEF) in the ionospheric E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly. Due to its importance, there is much interest in accurately measuring and modeling the EEF. In this work we propose a method of estimating the EEF using CHAMP satellite-derived latitudinal current profiles of the daytime EEJ along with Δ H measurements from ground magnetometer stations. Magnetometer station pairs in both Africa and South America were used for this study to produce time series of electrojet current profiles. These current profiles were then inverted for estimates of the EEF by solving the governing electrostatic equations. We compare our results with the Ion Velocity Meter (IVM) instrument on board the Communication/Navigation Outage Forecasting System satellite. We find high correlations of about 80% with the IVM data; however, we also find a constant offset of about 0.3 mV/m between the two data sets in Africa. Further investigation is needed to determine its cause. We compare the EEF structure in Africa and South America and find differences which can be attributed to the effect of atmospheric nonmigrating tides. This technique can be extended to any pair of ground magnetometer stations which can capture the day-to-day strength of the EEJ. |
BibTeX:
@article{Alken:2013,
author = {P. Alken and A. Chulliat and S. Maus},
title = {Longitudinal and seasonal structure of the ionospheric equatorial electric field},
journal = {Journal of Geophysical Research: Space Physics},
publisher = {Wiley-Blackwell},
year = {2013},
volume = {118},
number = {3},
pages = {1298--1305},
doi = {10.1029/2012ja018314}
}
|
| Chambodut A, Marchaudon A, Menvielle M, El-Lemdani Mazouz F and Lathuillére C (2013),
"The K -derived MLT sector geomagnetic indices", Geophysical Research Letters. Vol. 40(18), pp. 4808-4812. Wiley-Blackwell. |
| Abstract: New subauroral K-derived sector indices are proposed. They are based on the K local geomagnetic activity indices from the planetary am network stations, and their derivation scheme draws directly from that of am indices. Four Magnetic Local Time (MLT) sectors are considered, leading to four different K-derived MLT sector indices: the aσDawn (03–09 MLT), aσNoon (09–15 MLT), aσDusk (15–21 MLT), and aσMidnight (21–03 MLT) indices. They cover more than four solar cycles and, thus, allow robust statistical analysis. Statistical studies of the whole aσ data series and case studies for two geomagnetic storms are presented. These analyses clearly show that the four aσ have specific behaviors and that it is possible to get insight into both the statistical properties of the physical processes responsible for the observed geomagnetic activity and contribution to the dynamics of a given storm. |
BibTeX:
@article{Chambodut:2013,
author = {A. Chambodut and A. Marchaudon and M. Menvielle and El-Lemdani Mazouz, F. and C. Lathuillére},
title = {The K -derived MLT sector geomagnetic indices},
journal = {Geophysical Research Letters},
publisher = {Wiley-Blackwell},
year = {2013},
volume = {40},
number = {18},
pages = {4808--4812},
url = {https://doi.org/10.1002/grl.50947},
doi = {10.1002/grl.50947}
}
|
| Chulliat A, Vigneron P, Thébault E, Sirol O and Hulot G (2013),
"Swarm SCARF Dedicated Ionospheric Field Inversion chain", Earth, Planets and Space. Vol. 65(11), pp. 1271-1283. Springer Nature. |
| Abstract: The geomagnetic daily variation at mid-to-low latitudes, referred to as the geomagnetic Sq field, is generated by electrical currents within the conducting layers of the ionosphere on the dayside of the Earth. It is enhanced in a narrow equatorial band, due to the equatorial electrojet. The upcoming ESA Swarm satellite mission, to be launched end of 2013, will consist of three satellites in low-Earth orbit, providing a dense spatial and temporal coverage of the ionospheric Sq field. A Satellite Constellation Application and Research Facility (SCARF) has been set up by a consortium of research institutions, aiming at producing various level-2 data products during the Swarm mission. The Dedicated Ionospheric Field Inversion (DIFI) chain is a SCARF algorithm calculating global, spherical harmonic models of the Sq field at quiet times. It describes seasonal and solar cycle variations, separates primary and induced magnetic fields based upon advanced 3D-models of the mantle electrical conductivity, and relies on core, lithospheric and magnetospheric field models derived from other SCARF algorithms for removing non-ionospheric fields from the data. The DIFI chain was thoroughly tested on synthetic data during the SCARF preparation phase; it is now ready to be used for deriving models from real Swarm data. |
BibTeX:
@article{Chulliat:2013,
author = {Arnaud Chulliat and Pierre Vigneron and Erwan Thébault and Olivier Sirol and Gauthier Hulot},
title = {Swarm SCARF Dedicated Ionospheric Field Inversion chain},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2013},
volume = {65},
number = {11},
pages = {1271--1283},
doi = {10.5047/eps.2013.08.006}
}
|
| Love J and Chulliat A (2013),
"An International Network of Magnetic Observatories", Eos, Transactions American Geophysical Union. Vol. 94(42), pp. 373-374. Wiley-Blackwell. |
| Abstract: Since its formation in the late 1980s, the International Real-Time Magnetic Observatory Network (INTERMAGNET), a voluntary consortium of geophysical institutes from around the world, has promoted the operation of magnetic observatories according to modern standards [e.g., Rasson, 2007]. INTERMAGNET institutes have cooperatively developed infrastructure for data exchange and management as well as methods for data processing and checking. INTERMAGNET institutes have also helped to expand global geomagnetic monitoring capacity, most notably by assisting magnetic observatory institutes in economically developing countries by working directly with local geophysicists. |
BibTeX:
@article{Love:2013,
author = {Jeffrey Love and Arnaud Chulliat},
title = {An International Network of Magnetic Observatories},
journal = {Eos, Transactions American Geophysical Union},
publisher = {Wiley-Blackwell},
year = {2013},
volume = {94},
number = {42},
pages = {373--374},
doi = {10.1002/2013eo420001}
}
|
| Olsen N, Friis-Christensen E, Floberghagen R, Alken P, Beggan CD, Chulliat A, Doornbos E, da Encarnação JT, Hamilton B, Hulot G, van den IJssel J, Kuvshinov A, Lesur V, Lühr H, Macmillan S, Maus S, Noja M, Olsen PEH, Park J, Plank G, Püthe C, Rauberg J, Ritter P, Rother M, Sabaka TJ, Schachtschneider R, Sirol O, Stolle C, Thébault E, Thomson AWP, Tøffner-Clausen L, Velmský J, Vigneron P and Visser PN (2013),
"The Swarm Satellite Constellation Application and Research Facility (SCARF) and Swarm data products", Earth, Planets and Space. Vol. 65(11), pp. 1189-1200. Springer Nature. |
| Abstract: Swarm, a three-satellite constellation to study the dynamics of the Earth’s magnetic field and its interactions with the Earth system, is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system by improving our understanding of the Earth’s interior and environment. In order to derive advanced models of the geomagnetic field (and other higher-level data products) it is necessary to take explicit advantage of the constellation aspect of Swarm. The Swarm SCARF (SatelliteConstellationApplication andResearchFacility) has been established with the goal of deriving Level-2 products by combination of data from the three satellites, and of the various instruments. The present paper describes the Swarm input data products (Level-1b and auxiliary data) used by SCARF, the various processing chains of SCARF, and the Level-2 output data products determined by SCARF. |
BibTeX:
@article{Olsen:2013,
author = {Nils Olsen and Eigil Friis-Christensen and Rune Floberghagen and Patrick Alken and Ciaran D. Beggan and Arnaud Chulliat and Eelco Doornbos and João Teixeira da Encarnação and Brian Hamilton and Gauthier Hulot and Jose van den IJssel and Alexey Kuvshinov and Vincent Lesur and Hermann Lühr and Susan Macmillan and Stefan Maus and Max Noja and Poul Erik H. Olsen and Jaeheung Park and Gernot Plank and Christoph Püthe and Jan Rauberg and Patricia Ritter and Martin Rother and Terence J. Sabaka and Reyko Schachtschneider and Olivier Sirol and Claudia Stolle and Erwan Thébault and Alan W. P. Thomson and Lars Tøffner-Clausen and Jakub Velmský and Pierre Vigneron and Pieter N. Visser},
title = {The Swarm Satellite Constellation Application and Research Facility (SCARF) and Swarm data products},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2013},
volume = {65},
number = {11},
pages = {1189--1200},
doi = {10.5047/eps.2013.07.001}
}
|
| Thébault E, Vigneron P, Maus S, Chulliat A, Sirol O and Hulot G (2013),
"Swarm SCARF Dedicated Lithospheric Field Inversion chain", Earth, Planets and Space. Vol. 65(11), pp. 1257-1270. Springer Nature. |
| Abstract: The forthcoming Swarm satellite mission is a constellation of three satellites dedicated to the study of the geomagnetic field. The orbital characteristics of the mission, which includes a pair of satellites flying side by side, has prompted new efforts in data processing and modeling. A consortium of several research institutions has been selected by the European Space Agency (ESA) to provide a number of Level-2 data products which will be made available to the scientific community. Within this framework, specific tools have been tailor-made to better recover the lithospheric magnetic field contribution. These tools take advantage of gradient properties measured by the lower pair of Swarm satellites and rely on a regional modeling scheme designed to better detect signatures of small spatial scales. We report on a processing chain specifically designed for the Swarm mission. Using an End-to-End simulation, we show that the tools developed are operational. The chain generates a model that meets the primary scientific objectives of the Swarm mission. We also discuss refinements that could also be implemented during the Swarm operational phase to further improve lithospheric field models and reach unprecedented spatial resolution. |
BibTeX:
@article{Thebault:2013,
author = {E. Thébault and P. Vigneron and S. Maus and A. Chulliat and O. Sirol and G. Hulot},
title = {Swarm SCARF Dedicated Lithospheric Field Inversion chain},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2013},
volume = {65},
number = {11},
pages = {1257--1270},
doi = {10.5047/eps.2013.07.008}
}
|
| Cid C, Cremades H, Aran A, Mandrini C, Sanahuja B, Schmieder B, Menvielle M, Rodriguez L, Saiz E, Cerrato Y, Dasso S, Jacobs C, Lathuillere C and Zhukov A (2012),
"Can a halo CME from the limb be geoeffective?", Journal of Geophysical Research: Space Physics. Vol. 117(A11), pp. n/a-n/a. Wiley-Blackwell. |
| Abstract: The probability for a halo coronal mass ejection (CME) to be geoeffective is assumed to be higher the closer the CME launch site is located to the solar central meridian. However, events far from the central meridian may produce severe geomagnetic storms, like the case in April 2000. In this work, we study the possible geoeffectiveness of full halo CMEs with the source region situated at solar limb. For this task, we select all limb full halo (LFH) CMEs that occurred during solar cycle 23, and we search for signatures of geoeffectiveness between 1 and 5 days after the first appearance of each CME in the LASCO C2 field of view. When signatures of geomagnetic activity are observed in the selected time window, interplanetary data are carefully analyzed in order to look for the cause of the geomagnetic disturbance. Finally, a possible association between geoeffective interplanetary signatures and every LFH CME in solar cycle 23 is checked in order to decide on the CME's geoeffectiveness. After a detailed analysis of solar, interplanetary, and geomagnetic data, we conclude that of the 25 investigated events, there are only four geoeffective LFH CMEs, all coming from the west limb. The geoeffectiveness of these events seems to be moderate, turning to intense in two of them as a result of cumulative effects from previous mass ejections. We conclude that ejections from solar locations close to the west limb should be considered in space weather, at least as sources of moderate disturbances. |
BibTeX:
@article{Cid:2012,
author = {C. Cid and H. Cremades and A. Aran and C. Mandrini and B. Sanahuja and B. Schmieder and M. Menvielle and L. Rodriguez and E. Saiz and Y. Cerrato and S. Dasso and C. Jacobs and C. Lathuillere and A. Zhukov},
title = {Can a halo CME from the limb be geoeffective?},
journal = {Journal of Geophysical Research: Space Physics},
publisher = {Wiley-Blackwell},
year = {2012},
volume = {117},
number = {A11},
pages = {n/a--n/a},
url = {https://doi.org/10.1029/2012ja017536},
doi = {10.1029/2012ja017536}
}
|
| Love J and Chulliat A (2012),
"INTERMAGNET and Magnetic Observatories", EPOS newsletter. Vol. 12 [BibTeX] |
BibTeX:
@article{Love:2012,
author = {Love, J. and A. Chulliat},
title = {INTERMAGNET and Magnetic Observatories},
journal = {EPOS newsletter},
year = {2012},
volume = {12}
}
|
| Soloviev A, Agayan SM, Gvishiani AD, Bogoutdinov SR and Chulliat A (2012),
"Recognition of disturbances with specified morphology in time series: Part 2. Spikes on 1-s magnetograms", Izvestiya, Physics of the Solid Earth. Vol. 48(5), pp. 395-409. Pleiades Publishing Ltd. |
| Abstract: Preliminary magnetograms contain different types of temporal anthropogenic disturbances: spikes, baseline jumps, drifts, etc. These disturbances should be identified and filtered out during the preprocessing of the preliminary records for the definitive data. As of now, at the geomagnetic observatories, such filtering is carried out manually. Most of the disturbances in the records sampled every second are spikes, which are much more abundant than those on the magnetograms sampled every minute. Another important feature of the 1-s magnetograms is the presence of a plenty of specific disturbances caused by short-period geomagnetic pulsations, which must be retained in the definitive records. Thus, creating an instrument for formalized and unified recognition of spikes on the preliminary 1-s magnetograms would largely solve the problem of labor-consuming manual preprocessing of the magnetic records. In the context of this idea, in the present paper, we focus on recognition of the spikes on the 1-s magnetograms as a key point of the problem. We describe here the new algorithm of pattern recognition, SPs, which is capable of automatically identifying the spikes on the 1-s magnetograms with a low probability of missed events and false alarms. The algorithm was verified on the real magnetic data recorded at the French observatory located on Easter Island in the Pacific. |
BibTeX:
@article{Soloviev:2012b,
author = {A. Soloviev and S. M. Agayan and A. D. Gvishiani and Sh. R. Bogoutdinov and A. Chulliat},
title = {Recognition of disturbances with specified morphology in time series: Part 2. Spikes on 1-s magnetograms},
journal = {Izvestiya, Physics of the Solid Earth},
publisher = {Pleiades Publishing Ltd},
year = {2012},
volume = {48},
number = {5},
pages = {395--409},
doi = {10.1134/s106935131204009x}
}
|
| Soloviev A, Chulliat A, Bogoutdinov S, Gvishiani A, Agayan S, Peltier A and Heumez B (2012),
"Automated recognition of spikes in 1 Hz data recorded at the Easter Island magnetic observatory", Earth, Planets and Space. Vol. 64(9), pp. 743-752. Springer Nature. |
| Abstract: Preliminary magnetograms contain different types of temporal anthropogenic disturbances: spikes, baseline jumps, drifts, etc. These disturbances should be identified and filtered out during the preprocessing of the preliminary records for the definitive data. As of now, at the geomagnetic observatories, such filtering is carried out manually. Most of the disturbances in the records sampled every second are spikes, which are much more abundant than those on the magnetograms sampled every minute. Another important feature of the 1-s magnetograms is the presence of a plenty of specific disturbances caused by short-period geomagnetic pulsations, which must be retained in the definitive records. Thus, creating an instrument for formalized and unified recognition of spikes on the preliminary 1-s magnetograms would largely solve the problem of labor-consuming manual preprocessing of the magnetic records. In the context of this idea, in the present paper, we focus on recognition of the spikes on the 1-s magnetograms as a key point of the problem. We describe here the new algorithm of pattern recognition, SPs, which is capable of automatically identifying the spikes on the 1-s magnetograms with a low probability of missed events and false alarms. The algorithm was verified on the real magnetic data recorded at the French observatory located on Easter Island in the Pacific. |
BibTeX:
@article{Soloviev:2012,
author = {Anatoly Soloviev and Arnaud Chulliat and Shamil Bogoutdinov and Alexei Gvishiani and Sergey Agayan and Aline Peltier and Benoit Heumez},
title = {Automated recognition of spikes in 1 Hz data recorded at the Easter Island magnetic observatory},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2012},
volume = {64},
number = {9},
pages = {743--752},
doi = {10.5047/eps.2012.03.004}
}
|
| Vennerstrom S, Menvielle M, Merayo J and Falkenberg T (2012),
"Magnetic activity at Mars - Mars Surface Magnetic Observatory", Planetary and Space Science. Vol. 73(1), pp. 364-375. Elsevier BV. |
| Abstract: We use the extensive database of magnetic observations from the Mars Global Surveyor to investigate magnetic disturbances in the Martian space environment statistically, both close to and far from crustal anomalies. We discuss the results in terms of possible ionospheric and magnetospheric currents, and use this to provide an estimate of the expected magnetic disturbances at the Martian surface. Far from crustal anomaly regions the expected magnetic disturbances originating from currents associated with the induced magnetosphere are very weak at the day-side, but most likely larger on the night-side. Close to crustal anomalies the expected surface perturbation is larger and more variable both in space and time. It is important to note that these variations are not confined to the intense crustal anomalies in the southern hemisphere, but occur in large parts of the equatorial region. The disturbances around medium intensity radial anomalies in the equatorial region appear to derive from local current loops or vortices around cusp-like radial fields, acting to partly cancel the crustal field. The radial perturbation is further found to depend on upstream solar wind dynamic pressure. We define a magnetic experiment at the martian surface, the Mars Surface Magnetic Observatory (MSMO) including the science objectives, science experiment requirements, instrument and basic operations. We find the experiment to be feasible within the constraints of proposed stationary landing platforms. |
BibTeX:
@article{Vennerstrom:2012,
author = {S. Vennerstrom and M. Menvielle and J.M.G. Merayo and T.V. Falkenberg},
title = {Magnetic activity at Mars - Mars Surface Magnetic Observatory},
journal = {Planetary and Space Science},
publisher = {Elsevier BV},
year = {2012},
volume = {73},
number = {1},
pages = {364--375},
doi = {10.1016/j.pss.2012.08.001}
}
|
| Bernard A, Menvielle M and Chambodut A (2011),
"On the influence of data sampling interval on computer-derived K-indices", Data Science Journal. Vol. 10, pp. 41-46. |
| Abstract: The K index was devised by Bartels et al. (1939) to provide an objective monitoring of irregular geomagnetic activity. The K index was then routinely used to monitor the magnetic activity at permanent magnetic observatories as well as at temporary stations. The increasing number of digital and sometimes unmanned observatories and the creation of INTERMAGNET put the question of computer production of K at the centre of the debate. Four algorithms were selected during the Vienna meeting (1991) and endorsed by IAGA for the computer production of K indices. We used one of them (FMI algorithm) to investigate the impact of the geomagnetic data sampling interval on computer produced K values through the comparison of the computer derived K values for the period 2009, January 1st to 2010, May 31st at the Port-aux-Francais magnetic observatory using magnetic data series with different sampling rates (the smaller: 1 second; the larger: 1 minute). The impact is investigated on both 3-hour range values and K indices data series, as a function of the activity level for low and moderate geomagnetic activity. |
BibTeX:
@article{Bernard:2011,
author = {Bernard, A. and M. Menvielle and A. Chambodut},
title = {On the influence of data sampling interval on computer-derived K-indices},
journal = {Data Science Journal},
year = {2011},
volume = {10},
pages = {41-46},
doi = {10.2481/dsj.IAGA-07}
}
|
| Manoj C, Maus S and Chulliat A (2011),
"Observation of Magnetic Fields Generated by Tsunamis", Eos, Transactions American Geophysical Union (AGU). Vol. 92(2), pp. 13-14. |
| Abstract: Tsunamis produce perturbations in the Earth’s magnetic field by electromagnetic induction. Recent deployments of highly accurate magnetometers and the exceptionally deep solar minimum provided ideal conditions to observe these small signals from the tsunami resulting from the strong Chilean earthquake on 27 February 2010. Magnetic observatory measurements on Easter Island, 3500 kilometers west of the epicenter, shows periodic signal of 1 nanotesla, coincident in time with recordings from the local tide gauge. The detection of these magnetic signals represents a milestone in understanding tsunami-induced electromagnetic effects. |
BibTeX:
@article{Manoj:2011,
author = {Manoj, C. and S. Maus and A. Chulliat},
title = {Observation of Magnetic Fields Generated by Tsunamis},
journal = {Eos, Transactions American Geophysical Union (AGU)},
year = {2011},
volume = {92},
number = {2},
pages = {13-14},
doi = {10.1029/eost2011eo02}
}
|
| Marusenkov A, Chambodut A, Schott J and Korepanov V (2011),
"Observatory magnetometer in-situ calibration", Data Science Journal. Vol. 10, pp. 102-108. |
| Abstract: An experimental validation of the in-situ calibration procedure, which allows estimating parameters of observatory magnetometers (scale factors, sensor misalignment) without its operation interruption, is presented. In order to control the validity of the procedure, the records provided by two magnetometers calibrated independently in a coil system have been processed. The in-situ estimations of the parameters are in very good agreement with the values provided by the coil system calibration. |
BibTeX:
@article{Marusenkov:2011,
author = {Marusenkov, A. and A. Chambodut and Schott, J.J. and V. Korepanov},
title = {Observatory magnetometer in-situ calibration},
journal = {Data Science Journal},
year = {2011},
volume = {10},
pages = {102-108},
doi = {10.2481/dsj.IAGA-21}
}
|
| McCreadie H and Menvielle M (2011),
"Corrigendum to "The PC index: review of methods" published in Ann. Geophys., 28, 1887-1903, 2010", Annales Geophysicae. Vol. 29(5), pp. 813-814. Copernicus GmbH. |
| Abstract: In the paper “The PC Index: Review of methods.” by H. McCreadie and M. Menvielle (Ann. Geophys., 28, 1887–1903, 2010), typographic errors and lack of precision in the text have been found. The corresponding corrections and clarifications are given. |
BibTeX:
@article{McCreadie:2011,
author = {H. McCreadie and M. Menvielle},
title = {Corrigendum to "The PC index: review of methods" published in Ann. Geophys., 28, 1887-1903, 2010},
journal = {Annales Geophysicae},
publisher = {Copernicus GmbH},
year = {2011},
volume = {29},
number = {5},
pages = {813--814},
doi = {10.5194/angeo-29-813-2011}
}
|
| Chambodut A, Di Mauro D, Schott J, Bordais P, Agnoletto L and Di Felice P (2010),
"Three years continuous record of the Earth's magnetic field at Concordia Station (Dome-C, Antarctica)", Annals of Geophysics. Vol. 52(1) |
| Abstract: The magnetic observatory deployed at DomeC, Antarctica, in the French-Italian base known as Concordia has now been permanently running for more than three years. This paper focuses on these long-term results which are more relevant for an observatory intended to provide absolute values of the field. The problems which emerged in this fairly long record are discussed and solutions suggested to upgrade the observatory to the standards of an absolute one (i.e. Intermagnet standards). |
BibTeX:
@article{Chambodut:2010,
author = {Chambodut, A. and Di Mauro, D. and Schott, J.J. and Bordais, P. and Agnoletto, L. and Di Felice, P.},
title = {Three years continuous record of the Earth's magnetic field at Concordia Station (Dome-C, Antarctica)},
journal = {Annals of Geophysics},
year = {2010},
volume = {52},
number = {1},
doi = {10.4401/ag-4569}
}
|
| Chambodut A, Langlais B, Menvielle M, Thébault E, Chulliat A and Hulot G (2010),
"Candidate models for the IGRF-11th generation making use of extrapolated observatory data", Earth, Planets and Space. Vol. 62(10), pp. 745-751. Springer Nature. |
| Abstract: Three candidate models are produced in response to the call for IGRF-11 models. A main field model around epoch 2005.0 is based on one year of Ørsted and CHAMP measurements, and is proposed for the definitive model for epoch 2005.0. A main field model around epoch 2009.5, based on two months of CHAMP measurements and extrapolated to 2010.0, is proposed as a main field model for epoch 2010.0. A secular variation model valid for 2010.0–2015.0, based on the extrapolation through exponential smoothing of observatory monthly mean values, is proposed as a predictive secular variation model. Comparison of similar extrapolations made for previous IGRF generations with actual observations are presented and discussed. |
BibTeX:
@article{Chambodut:2010c,
author = {Aude Chambodut and Benoit Langlais and Michel Menvielle and Erwan Thébault and Arnaud Chulliat and Gauthier Hulot},
title = {Candidate models for the IGRF-11th generation making use of extrapolated observatory data},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2010},
volume = {62},
number = {10},
pages = {745--751},
doi = {10.5047/eps.2010.06.006}
}
|
| Chulliat A, Hulot G and Newitt LR (2010),
"Magnetic flux expulsion from the core as a possible cause of the unusually large acceleration of the north magnetic pole during the 1990s", Journal of Geophysical Research. Vol. 115(B7) Wiley-Blackwell. |
| Abstract: The north magnetic pole (NMP) has been drifting in a north-northwesterly direction since the 19th century. Both local surveys and geomagnetic models derived from observatory and satellite data show that the NMP suddenly accelerated during the 1990s. Its speed increased from about 15 km/yr in 1989 to about 60 km/yr in 2002, after which it started to decrease slightly. Using a Green's function, we show that this acceleration is mainly caused by a large, negative secular variation change in the radial magnetic field at the core surface, under the New Siberian Islands. This change occurs in a region of the core surface where there is a pair of secular variation patches of opposite polarities, which we suggest could be the signature of a so-called “polar magnetic upwelling” of the type observed in some recent numerical dynamo simulations. Indeed, a local analysis of the radial secular variation and magnetic field gradient suggests that the secular variation change under the New Siberian Islands is likely to be accompanied by a significant amount of magnetic diffusion, in agreement with such a mechanism. We thus hypothesize that the negative secular variation change under the New Siberian Islands that produced the NMP acceleration could result from a slowdown of the polar magnetic upwelling during the 1990s. We finally note that the NMP drift speed is determined by such a combination of factors that it is at present not possible to forecast its future evolution. |
BibTeX:
@article{Chulliat:2010b,
author = {A. Chulliat and G. Hulot and L. R. Newitt},
title = {Magnetic flux expulsion from the core as a possible cause of the unusually large acceleration of the north magnetic pole during the 1990s},
journal = {Journal of Geophysical Research},
publisher = {Wiley-Blackwell},
year = {2010},
volume = {115},
number = {B7},
doi = {10.1029/2009jb007143}
}
|
| Chulliat A, Hulot G, Newitt LR and Orgeval J-j (2010),
"What Caused Recent Acceleration of the North Magnetic Pole Drift?", Eos Trans. AGU. Vol. 91(51), pp. 501-502. |
| Abstract: The north magnetic pole (NMP) is the point at the Earth's surface where the geomagnetic field is directed vertically downward. It drifts in time as a result of core convection, which sustains the Earth's main magnetic field through the geodynamo process. During the 1990s the NMP drift speed suddenly increased from 15 kilometers per year at the start of the decade to 55 kilometers per year by the decade's end. This acceleration was all the more surprising given that the NMP drift speed had remained less than 15 kilometers per year over the previous 150 years of observation. |
BibTeX:
@article{Chulliat:2010c,
author = {Chulliat, A. and G. Hulot and L. R. Newitt and J.-j. Orgeval},
title = {What Caused Recent Acceleration of the North Magnetic Pole Drift?},
journal = {Eos Trans. AGU},
year = {2010},
volume = {91},
number = {51},
pages = {501-502},
doi = {10.1029/2010EO510001}
}
|
| Chulliat A and Olsen N (2010),
"Observation of magnetic diffusion in the Earth's outer core from Magsat, Ørsted, and CHAMP data", Journal of Geophysical Research. Vol. 115(B5) Wiley-Blackwell. |
| Abstract: The frozen flux assumption consists in neglecting magnetic diffusion in the core. It has been widely used to compute core flows from geomagnetic observations. Here we investigate the validity of this assumption over the time interval 1980–2005, using high-precision magnetic data from the Magsat, Ørsted, and CHAMP satellites. A detectable change of magnetic fluxes through patches delimited by curves of zero radial magnetic field at the core-mantle boundary is associated with a failure of the frozen flux assumption. For each epoch (1980 and 2005), we calculate spatially regularized models of the core field which we use to investigate the change of reversed magnetic flux at the core surface. The largest and most robust change of reversed flux is observed for two patches: one located under St. Helena Island (near 20°S, 15°E); the other, much larger, is located under the South Atlantic Ocean. We next calculate frozen-flux-constrained field models (i.e., pairs of models for epoch 1980 and 2005 having the same flux through patches delimited by curves of zero radial magnetic field), using a penalty method. We find that the frozen flux constraint does not lead to any significant increase of the global misfit. However, applying the constraint leads to a detectable increase of the scalar residuals at satellite altitude in the region of St. Helena, strongly suggesting a local failure of the frozen flux assumption. The observed flux expulsion within the St. Helena patch could result from the formation of a pair of “core spots,” as predicted by numerical simulations of the geodynamo. |
BibTeX:
@article{Chulliat:2010,
author = {A. Chulliat and N. Olsen},
title = {Observation of magnetic diffusion in the Earth's outer core from Magsat, Ørsted, and CHAMP data},
journal = {Journal of Geophysical Research},
publisher = {Wiley-Blackwell},
year = {2010},
volume = {115},
number = {B5},
doi = {10.1029/2009jb006994}
}
|
| Chulliat A and Thébault E (2010),
"Testing IGRF-11 candidate models against CHAMP data and quasi-definitive observatory data", Earth, Planets and Space. Vol. 62(10), pp. 805-814. Springer Nature. |
| Abstract: As part of the evaluation of IGRF-11 candidate models, we compared candidate models and actual measurements. We first carried out a residual analysis between main field candidates and CHAMP data, which were pre-processed and corrected for the secular variation and the lithospheric, external and oceanic fields. For epoch 2005.0, one model (D) is abnormally far from the testing dataset, while four models (A, B, F, G) have the smallest data residuals. For 2010.0, three models (B, F, G) have smaller data residuals than other models. These results, although biased toward models relying on datasets close to the testing datasets (B, F), usefully complement the results of intercomparisons between models. We next tested secular variation candidate models for 2010–2015 against annual differences of (a) definitive monthly means in 2007 and 2008 at 86 observatories, and (b) quasi-definitive monthly means from January to October 2009 at nine observatories where this new type of data was produced. Quasi-definitive data are found to significantly improve the discriminating effect of the test, favoring models obtained at epochs close to the end of 2009 (B, F) and penalizing some extrapolated models (G). They also enable a truly independent validation of the candidate models. |
BibTeX:
@article{Chulliat:2010e,
author = {Arnaud Chulliat and Erwan Thébault},
title = {Testing IGRF-11 candidate models against CHAMP data and quasi-definitive observatory data},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2010},
volume = {62},
number = {10},
pages = {805--814},
doi = {10.5047/eps.2010.06.004}
}
|
| Chulliat A, Thébault E and Hulot G (2010),
"Core field acceleration pulse as a common cause of the 2003 and 2007 geomagnetic jerks", Geophysical Research Letters. Vol. 37(7) Wiley-Blackwell. |
| Abstract: Using observatory data, we report the detection of a geomagnetic jerk in 2007, which we relate to a jump in the second derivative of the geomagnetic field previously noted in satellite data. Although not of worldwide extent, this jerk is very intense in the South Atlantic region. Using the CHAOS-2 model, we show that both this jerk and the previous 2003 jerk are caused by a single core field acceleration pulse reaching its maximum power near 2006.0. This pulse seems to be simultaneously occurring in several regions of the core surface where it corresponds to dominant n = 5 and 6 spherical harmonic modes. Geometrical attenuation explains why the 2003 and 2007 jerks are local and not fully synchronized at the Earth's surface. Our results suggest that this core field acceleration pulse is the relevant phenomenon to be investigated from the point of view of core dynamics, rather than the jerks themselves. |
BibTeX:
@article{Chulliat:2010d,
author = {A. Chulliat and E. Thébault and G. Hulot},
title = {Core field acceleration pulse as a common cause of the 2003 and 2007 geomagnetic jerks},
journal = {Geophysical Research Letters},
publisher = {Wiley-Blackwell},
year = {2010},
volume = {37},
number = {7},
doi = {10.1029/2009gl042019}
}
|
| Finlay C, Maus S, Beggan C, Bondar T, Chambodut A, Chernova T, Chulliat A, Golokov V, Hamilton B, Hamoudi M, Holme R, Hulot G, Kuang W, Langlais B, Lesur V, Lowes F, Lühr H, Macmillan S, Mandea M, McLean S, Manoj C, Menvielle M, Michaelis I, Olsen N, Rauberg J, Rother M, Sabaka T, Tangborn A, Toffner-Clausen L, Thebault E, Thomson A, Wardinski I, Wei Z and Zvereva T (2010),
"International Geomagnetic Reference Field: The Eleventh Generation.", Geophys. J. Int.. Vol. 183(3), pp. 1216-1230. |
| Abstract: The eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0–2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0–2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined. |
BibTeX:
@article{Finlay:2010,
author = {C.C. Finlay and S. Maus and C.D. Beggan and T.N. Bondar and A. Chambodut and T.A. Chernova and A. Chulliat and V.P. Golokov and B. Hamilton and M. Hamoudi and R. Holme and G. Hulot and W. Kuang and B. Langlais and V. Lesur and F.J. Lowes and H. Lühr and S. Macmillan and M. Mandea and S. McLean and C. Manoj and M. Menvielle and I. Michaelis and N. Olsen and J. Rauberg and M. Rother and T.J. Sabaka and A. Tangborn and L. Toffner-Clausen and E. Thebault and A.W.P. Thomson and I. Wardinski and Z. Wei and T.I. Zvereva},
title = {International Geomagnetic Reference Field: The Eleventh Generation.},
journal = {Geophys. J. Int.},
year = {2010},
volume = {183},
number = {3},
pages = {1216-1230},
doi = {10.1111/j.1365-246X.2010.04804.x}
}
|
| Finlay CC, Dumberry M, Chulliat A and Pais MA (2010),
"Short Timescale Core Dynamics: Theory and Observations", Space Science Reviews. Vol. 155(1-4), pp. 177-218. Springer Nature. |
| Abstract: Fluid motions in the Earth’s core produce changes in the geomagnetic field (secular variation) and are also an important ingredient in the planet’s rotational dynamics. In this article we review current understanding of core dynamics focusing on short timescales of years to centuries. We describe both theoretical models and what may be inferred from geomagnetic and geodetic observations. The kinematic concepts of frozen flux and magnetic diffusion are discussed along with relevant dynamical regimes of magnetostrophic balance, tangential geostrophy, and quasi-geostrophy. An introduction is given to free modes and waves that are expected to be present in Earth’s core including axisymmetric torsional oscillations and non-axisymmetric Magnetic-Coriolis waves. We focus on important recent developments and promising directions for future investigations. |
BibTeX:
@article{Finlay:2010b,
author = {C. C. Finlay and M. Dumberry and A. Chulliat and M. A. Pais},
title = {Short Timescale Core Dynamics: Theory and Observations},
journal = {Space Science Reviews},
publisher = {Springer Nature},
year = {2010},
volume = {155},
number = {1-4},
pages = {177--218},
doi = {10.1007/s11214-010-9691-6}
}
|
| Gobinddass M-L, Willis P, Menvielle M and Diament M (2010),
"Refining DORIS atmospheric drag estimation in preparation of ITRF2008", Advances in Space Research. Vol. 46(12), pp. 1566-1577. Elsevier BV. |
| Abstract: In preparation of ITRF2008, all geodetic technique services (VLBI, SLR, GPS and DORIS) are generating new solutions based on combination of individual analysis centers solutions. These data reprocessing are based on a selection of models, parameterization and estimation strategy unique to each analysis center and to each technique. While a good agreement can be found for models between groups, thanks to the existence of the IERS conventions, a great diversity still exist for parameter estimation, allowing possible future improvements in this direction. The goal of this study is to focus on the atmospheric drag estimation used to generate the new DORIS/IGN ignwd08 time series prepared for ITRF2008. We develop here a method to inter-compare different processing strategies. In a first step, by analyzing single-satellite solutions for a few weeks of data but for a large number of possible analysis strategies, we demonstrate that estimating drag coefficient more frequently (typically every 1–2 h instead of previously every 4–8 h) for the lowest DORIS satellites (SPOTs and Envisat) provides better geodetic results for station coordinates and polar motion. This new processing strategy also solved earlier problem found when processing DORIS data during intense geomagnetic events, such as geomagnetic storms. Differences between drag estimation strategies can mostly be found during these few specific periods of extreme geomagnetic activity (few days per year). In such a case, when drag coefficient is only estimated every 6 h or less often for single-satellite solution, a significant degradation in station coordinate accuracy can be observed (120 mm vs. 20 mm) and significant biases arose in polar motion estimation (5 mas vs. 0.3 mas). In a second step, we reprocessed a full year of DORIS data (2003) in a standard multi-satellite mode. We were able to provide statistics on a more reliable data set and to strengthen these conclusions. Our proposed DORIS analysis is easy to implement in all software packages and is now already used by several analysis centers of the International DORIS Service (IDS) when submitting reprocessed solutions for ITRF2008. |
BibTeX:
@article{Gobinddass:2010,
author = {Marie-Line Gobinddass and Pascal Willis and Michel Menvielle and Michel Diament},
title = {Refining DORIS atmospheric drag estimation in preparation of ITRF2008},
journal = {Advances in Space Research},
publisher = {Elsevier BV},
year = {2010},
volume = {46},
number = {12},
pages = {1566--1577},
doi = {10.1016/j.asr.2010.04.004}
}
|
| Lathuillère C and Menvielle M (2010),
"Comparison of the observed and modeled low- to mid-latitude thermosphere response to magnetic activity: Effects of solar cycle and disturbance time delay", Advances in Space Research. Vol. 45(9), pp. 1093-1100. Elsevier BV. |
| Abstract: The performance of JB2008 and NRLMSISE-00 models, in describing the response of the thermosphere to magnetic activity are evaluated against total mass density retrieved from accelerometer measurements made onboard CHAMP satellite during 5 years. We show that the global low- to mid-latitude disturbance amplitude is correctly described by the JB2008 model for low solar activity conditions and by both the JB2008 and the NRLMSISE-00 models for high solar activity conditions. For low solar activity conditions, statistics based on almost 3 years of data confirm the large underestimation by the NRLMSISE-00 model quantified by Lathuillère et al. (2008) for the year 2004. We also found that the time delay between low- to mid-latitude global thermosphere disturbance and magnetic activity is statistically well estimated by the NRLMSISE-00 and JB2008 models for disturbed conditions. For moderately disturbed conditions however, the time delay estimated by the JB2008 model is too large by about 3 h. For very disturbed conditions, we found different time delays during day-time and night-time, using new geomagnetic proxies with a 30-min time resolution. |
BibTeX:
@article{Lathuillre:2010,
author = {Chantal Lathuillère and Michel Menvielle},
title = {Comparison of the observed and modeled low- to mid-latitude thermosphere response to magnetic activity: Effects of solar cycle and disturbance time delay},
journal = {Advances in Space Research},
publisher = {Elsevier BV},
year = {2010},
volume = {45},
number = {9},
pages = {1093--1100},
doi = {10.1016/j.asr.2009.08.016}
}
|
| Matzka J, Chulliat A, Mandea M, Finlay CC and Qamili E (2010),
"Geomagnetic Observations for Main Field Studies: From Ground to Space", Space Science Reviews. Vol. 155(1-4), pp. 29-64. Springer Nature. |
| Abstract: Direct measurements of the geomagnetic field have been made for more than 400 years, beginning with individual determinations of the angle between geographic and magnetic North. This was followed by the start of continuous time series of full vector measurements at geomagnetic observatories and the beginning of geomagnetic repeat stations surveys in the 19th century. In the second half of the 20th century, true global coverage with geomagnetic field measurements was accomplished by magnetometer payloads on low-Earth-orbiting satellites. This article describes the procedures and instruments for magnetic field measurements on ground and in space and covers geomagnetic observatories, repeat stations, automatic observatories, satellites and historic observations. Special emphasis is laid on the global network of geomagnetic observatories. |
BibTeX:
@article{Matzka:2010,
author = {J. Matzka and A. Chulliat and M. Mandea and C. C. Finlay and E. Qamili},
title = {Geomagnetic Observations for Main Field Studies: From Ground to Space},
journal = {Space Science Reviews},
publisher = {Springer Nature},
year = {2010},
volume = {155},
number = {1-4},
pages = {29--64},
doi = {10.1007/s11214-010-9693-4}
}
|
| McCreadie H and Menvielle M (2010),
"The PC index: review of methods", Annales Geophysicae. Vol. 28(10), pp. 1887-1903. Copernicus GmbH. |
| Abstract: The Polar Cap (PC) index is a controversial topic within the IAGA scientific community. Since 1997 discussions of the validity of the index to be endorsed as an official IAGA index have ensued. There is no doubt as to the scientific merit of the index which is not discussed here. What is in doubt is the methodology of the derivation of the index by different groups. The Polar Cap index (PC: PCN, northern; PCS, southern) described in Troshichev et al. (2006) and Stauning et al. (2006), both termed the "unified PC index", and the PCN index routinely derived at DMI are inspected using only available published literature. They are found to contain different derivation procedures, thus are not unified. The descriptions of the derivation procedures are found to not be adequate to independently derive the PC indices. |
BibTeX:
@article{McCreadie:2010,
author = {McCreadie, H. and M. Menvielle},
title = {The PC index: review of methods},
journal = {Annales Geophysicae},
publisher = {Copernicus GmbH},
year = {2010},
volume = {28},
number = {10},
pages = {1887--1903},
doi = {10.5194/angeo-28-1887-2010}
}
|
| Peltier A and Chulliat A (2010),
"On the feasibility of promptly producing quasi-definitive magnetic observatory data", Earth, Planets and Space. Vol. 62(2), pp. e5-e8. Springer Nature. |
| Abstract: Magnetic observatories currently distribute two types of data: preliminary data, available in less than 72 hrs in the case of INTERMAGNET observatories, and definitive baseline-corrected data, produced only once a year. Several users and groups of users have expressed the need for baseline-corrected observatory data produced in a continuous manner. The main applications for such quasi-definitive data include geomagnetic field modeling and the calculation of geomagnetic activity indices. We present an original method for producing quasi-definitive data at the end of each calendar month using temporary baselines. Preliminary and definitive data at nine INTERMAGNET observatories are used to test this method, simulating the production of quasi-definitive data throughout the year 2008. The temporary baselines obtained are very close to the definitive ones, except during the last few days of each time interval. The means and standard deviations of the differences between quasi-definitive and definitive data do not exceed 0.3 nT, well below the current INTERMAGNET standard of accuracy. This result demonstrates the feasibility of promptly producing quasi-definitive data at most magnetic observatories of INTERMAGNET type. |
BibTeX:
@article{Peltier:2010,
author = {Aline Peltier and Arnaud Chulliat},
title = {On the feasibility of promptly producing quasi-definitive magnetic observatory data},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2010},
volume = {62},
number = {2},
pages = {e5--e8},
doi = {10.5047/eps.2010.02.002}
}
|
| Thébault E, Chulliat A, Maus S, Hulot G, Langlais B, Chambodut A and Menvielle M (2010),
"IGRF candidate models at times of rapid changes in core field acceleration", Earth, Planets and Space. Vol. 62(10), pp. 753-763. Springer Nature. |
| Abstract: We submit three candidate models following the call for IGRF-11. We apply a simple modeling approach in spherical harmonics based on a quadratic Taylor expansion for the internal field time variations. We use the Dst magnetic index as a proxy for the external field variations. In order to compensate for the limitations incurred by such a conventional approach, we focus on the optimal selection of satellite data in space and time. We also show that some a priori knowledge about the core field state helps us to avoid the pitfall encountered in the case of rapid changes of core field accelerations. Indeed, various acceleration events of relevance for the IGRF 11th occurred between 2003 and 2010, one of them being a geomagnetic jerk. They could entail disagreements between IGRF candidate models for the secular variation (SV) if data prior to 2008 are used. Our SV and main field (MF) candidate models have a root mean square uncertainty less than 6 nT/yr and 8 nT, respectively, with respect to the modeled magnetic field contributions. These values correspond to the intrinsic error associated with truncating SV and MF models to spherical harmonic degree 8 and 13, respectively, as requested for IGRF models. |
BibTeX:
@article{Thebault:2010,
author = {Erwan Thébault and Arnaud Chulliat and Stefan Maus and Gauthier Hulot and Benoit Langlais and Aude Chambodut and Michel Menvielle},
title = {IGRF candidate models at times of rapid changes in core field acceleration},
journal = {Earth, Planets and Space},
publisher = {Springer Nature},
year = {2010},
volume = {62},
number = {10},
pages = {753--763},
doi = {10.5047/eps.2010.05.004}
}
|