Earth's core magnetic field model Mag.num and the IGRF 13 candidate

<p>The Earth's core magnetic field model Mag.num was the parent model for the GFZ IGRF 13 candidate submission. The model is based on geomagnetic ground observatory and Swarm satellite observations. Epochs 2020.0 and beyond were not covered by the data available at the time of submission and our results were based on predictions. In this study, we investigate the effect of the more recent available data on our results of the 2020.0 epoch and the predicted secular variation by generating an updated Mag.num version. We especially focus on the spatial and temporal patterns of the local geomagnetic field minimum of the South Atlantic Anomaly (SAA). Recently, global geomagnetic field models have shown that an additional, although shallow, secondary minimum at Earth's surface has developed since around 2005. The location and significance of the secondary minimum and of the saddle point between the two minima are assessed also in view of the respective differences among the candidate models.</p>

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Steady flows at the top of Earth's core derived from geomagnetic field models

Journal of Geophysical Research Atmospheres ◽

10.1029/jb091ib12p12444 ◽

1986 ◽

Vol 91 (B12) ◽

pp. 12444-12466 ◽

Cited By ~ 84

Author(s):

Coerte V. Voorhies

Keyword(s):

Geomagnetic Field ◽

Steady Flows ◽

Earth’S Core ◽

Earth's Core ◽

Geomagnetic Field Models

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Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

Earth Planets and Space ◽

10.1186/s40623-020-01279-y ◽

2020 ◽

Vol 72 (1) ◽

Author(s):

Sabrina Sanchez ◽

Johannes Wicht ◽

Julien Bärenzung

Keyword(s):

Magnetic Field ◽

Secular Variation ◽

Geomagnetic Field ◽

Wave Number ◽

Main Magnetic Field ◽

Candidate Model ◽

Uncertainty Estimates ◽

Geomagnetic Field Models ◽

Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

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CM6: a comprehensive geomagnetic field model derived from both CHAMP and Swarm satellite observations

Earth Planets and Space ◽

10.1186/s40623-020-01210-5 ◽

2020 ◽

Vol 72 (1) ◽

Cited By ~ 4

Author(s):

Terence J. Sabaka ◽

Lars Tøffner-Clausen ◽

Nils Olsen ◽

Christopher C. Finlay

Keyword(s):

Geomagnetic Field ◽

Field Model ◽

Satellite Observations ◽

Geomagnetic Field Model ◽

Swarm Satellite

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Fast (non-)diffusive Quasi-Geostrophic Magneto-Coriolis Modes in the Earth's core

10.5194/egusphere-egu21-2176 ◽

2021 ◽

Author(s):

Felix Gerick ◽

Dominique Jault ◽

Jerome Noir

Keyword(s):

Magnetic Field ◽

Magnetic Energy ◽

Three Dimensional ◽

Outer Core ◽

Equatorial Region ◽

Earth’S Core ◽

Earth's Core ◽

Strong Focusing ◽

Geomagnetic Observations ◽

And Diffusion

<p>&#160;Fast changes of Earth's magnetic field could be explained by inviscid and diffusion-less quasi-geostrophic (QG) Magneto-Coriolis modes. We present a hybrid QG model with columnar flows and three-dimensional magnetic fields and find modes with periods of a few years at parameters relevant to Earth's core. These fast Magneto-Coriolis modes show strong focusing of their kinetic and magnetic energy in the equatorial region, while maintaining a relatively large spatial structure along the azimuthal direction. Their properties agree with some of the observations and inferred core flows. We find additionally, in contrast to what has been assumed previously, that these modes are not affected significantly by magnetic diffusion. The model opens a new way of inverting geomagnetic observations to the flow and magnetic field deep within the Earth's outer core.</p>

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Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

Annales Geophysicae ◽

10.5194/angeo-34-55-2016 ◽

2016 ◽

Vol 34 (1) ◽

pp. 55-65 ◽

Cited By ~ 4

Author(s):

A. D. M. Walker ◽

G. J. Sofko

Keyword(s):

Magnetic Field ◽

Steady State ◽

Electric Field ◽

Electric Fields ◽

Magnetic Field Line ◽

Geomagnetic Field ◽

Geomagnetic Field Models ◽

Spatial Derivatives ◽

Field Lines ◽

The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

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A case study of the plasma in the magneto-sheath using the numerical magnetosheath-magnetosphere model and THEMIS measure-ments

MATEC Web of Conferences ◽

10.1051/matecconf/201814503004 ◽

2018 ◽

Vol 145 ◽

pp. 03004

Author(s):

Polya Dobreva ◽

Olga Nitcheva ◽

Monio Kartalev

Keyword(s):

Magnetic Field ◽

Field Model ◽

Specific Aspect ◽

Plasma Parameters ◽

Ion Density ◽

Magnetic Field Model ◽

Wind Spacecraft ◽

The Mean ◽

The Magnetic Field

This paper presents a case study of the plasma parameters in the magnetosheath, based on THEMIS measurements. As a theoretical tool we apply the self-consistent magnetosheath-magnetosphere model. A specific aspect of the model is that the positions of the bow shock and the magnetopause are self-consistently determined. In the magnetosheath the distribution of the velocity, density and temperature is calculated, based on the gas-dynamic theory. The magnetosphere module allows for the calculation of the magnetopause currents, confining the magnetic field into an arbitrary non-axisymmetric magnetopause. The variant of the Tsyganenko magnetic field model is applied as an internal magnetic field model. As solar wind monitor we use measurements from the WIND spacecraft. The results show that the model quite well reproduces the values of the ion density and velocity in the magnetosheath. The simlicity of the model allows calulations to be perforemed on a personal computer, which is one of the mean advantages of our model.

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