Axial poloidal electromagnetic core-mantle coupling torque: A re-examination for different conductivity and satellite supported geomagnetic field models

Greiner-Mai, H.; Hagedoorn, Jan; Ballani, L.; Wardinski, Ingo; Stromeyer, Dietrich; Hengst, Rico

doi:10.1007/s11200-007-0029-0

Cited by 4 publications

(5 citation statements)

References 27 publications

(35 reference statements)

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“…This represents the magnetic field potential as a series of multipoles, where n = 1 represents the dipole contribution, and n = 2 represents the quadrupole contribution. In this study, the SHC up to degree and order ten are taken from the CHAOS-6 model as these coefficients are more related to the core activity [47]. As the GMJ events are detectable in the secular variation (SV) of the geomagnetic field, we investigate the rate of change of SV, estimated by the second derivative of GMF.…”

Section: Geomagnetic Field Modelmentioning

confidence: 99%

Towards Understanding the Interconnection between Celestial Pole Motion and Earth’s Magnetic Field Using Space Geodetic Techniques

Modiri

Heinkelmann

Belda

et al. 2021

Sensors

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The understanding of forced temporal variations in celestial pole motion (CPM) could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the Earth orientation parameters. Besides astronomical forcing, CPM excitation depends on the processes in the fluid core and the core–mantle boundary. The same processes are responsible for the variations in the geomagnetic field (GMF). Several investigations were conducted during the last decade to find a possible interconnection of GMF changes with the length of day (LOD) variations. However, less attention was paid to the interdependence of the GMF changes and the CPM variations. This study uses the celestial pole offsets (CPO) time series obtained from very long baseline interferometry (VLBI) observations and data such as spherical harmonic coefficients, geomagnetic jerk, and magnetic field dipole moment from a state-of-the-art geomagnetic field model to explore the correlation between them. In this study, we use wavelet coherence analysis to compute the correspondence between the two non-stationary time series in the time–frequency domain. Our preliminary results reveal interesting common features in the CPM and GMF variations, which show the potential to improve the understanding of the GMF’s contribution to the Earth’s rotation. Special attention is given to the corresponding signal between FCN and GMF and potential time lags between geomagnetic jerks and rotational variations.

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Section: Geomagnetic Field Modelmentioning

confidence: 99%

Towards Understanding the Interconnection between Celestial Pole Motion and Earth’s Magnetic Field Using Space Geodetic Techniques

Modiri

Heinkelmann

Belda

et al. 2021

Sensors

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“…Thus, we can only refer to other investigations indicative of the global conductivity, which are modelling of the electromagnetic core–mantle coupling for the decadal time scale, nutation, laboratory experiments and investigations of matter phases (see e.g. the overview in Greiner‐Mai et al 2007). By nutation studies of Buffett (1992), a shell of 0.2 km at the bottom of the mantle with σ= 5 × 10 5 S m −1 was found to be sufficient to explain the observations.…”

Section: Model Assumptions: Data and Conductivitymentioning

confidence: 99%

“…Moreover, sometimes in northern regions and with the model CM4, later jerk occurrence times are detected than with the model C 3 FM. These defects are probably produced by the different constraints used for generating these data sets (see also the discussion on the temporal behaviour of these geomagnetic field models in Greiner-Mai et al 2007).…”

Section: Influence Of Geomagnetic Field Modelsmentioning

confidence: 99%

The 1991 geomagnetic jerk as seen at the Earth's surface and the core-mantle boundary

Ballani

Hagedoorn

Wardinski

et al. 2010

Geophysical Journal International

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S U M M A R YWe determine the occurrence times of geomagnetic impulses (jerks) around the year 1991 in the three geomagnetic secular variation components for the Earth's surface by a simple optimization algorithm. The geomagnetic field models we use are the low-degree parts of the models CM4 and C 3 FM. We find that the temporal jerk pattern can be detected in fields (n ≤ 4), from which the spherical harmonic degrees n = 2 or n = 3 (tangential) and n = 4 (radial) are representative.To calculate the secular variation components at the core-mantle boundary (CMB) we apply the non-harmonic downward continuation (NHDC) method. For the mantle conductivity, three estimates, dependent on the radius, are assumed with conductances between 10 7 S and 2 × 10 8 S. The knowledge of the secular variation components at the CMB allows us to track the global distributions of jerk occurrence times in dependence on the mantle conductivity estimate.We find for each component a typically shaped, global topology for the location of the jerk occurrence times at the Earth's surface and the CMB. For the tangential (ϑ, ϕ)-components, these global topologies show always the well-known temporal bimodality on each surface. Another characteristic feature is found for the jerk of the r-component. It displays a double jerk centred around 1991 consisting of a v-shaped and a reversely v-shaped part, which are significantly correlated.Between the CMB and the Earth's surface, we find time delays in the range of 1-2 yr for the tangential and less than 1 yr for the radial jerk components. To understand these time delays, comparisons at fixed locations are carried out to check the influence of the respective conductivity function. For studying the time delay effects, we apply the inversion set-up of the NHDC to calculate simulated temporal oscillations and derive analytical expressions approximating the phase shifts. We find that jerk occurrence time delays and simulated phase shifts of temporal oscillations have a similar behaviour with respect to the influence of the conductivity and for the radial and the tangential components, respectively.In addition, a new concept for determining a jerk amplitude is presented briefly. This so-called dynamical jerk morphology, which forms a portion of the geomagnetic secular acceleration, is defined for each component by a time function on the considered surface. Its temporal motion patterns at the CMB are likely related with jerk originating processes in the fluid outer core.

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“…in the boundary condition) are related to processes in the Earth's core and are not significantly influenced by crustal magnetization or other processes (e.g. Greiner-Mai et al, 2007). In addition, we need for the determination of the toroidal geomagnetic field the field-generating scalar of the poloidal geomagnetic field (S ) at the CMB and the generating scalars (P and Q) of the surface fluid-flow velocity, u, in the outer core close to the CMB.…”

Section: Preparation Of Input Datamentioning

confidence: 99%

“…Holme, 1998b). A more detailed justification for the conductivity models chosen in our EM torque studies is given in a preliminary investigation of Greiner-Mai et al (2007) (see also Sec. 4).…”

Section: Introductionmentioning

confidence: 99%

Determining the time-variable part of the toroidal geomagnetic field in the core-mantle boundary zone

Hagedoorn

Greiner-Mai

Ballani

2010

Physics of the Earth and Planetary Interiors

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For the computation of the electromagnetic (EM) core-mantle coupling torque, the geomagnetic field must be known at the coremantle boundary (CMB). It can be divided into linearly independent poloidal and toroidal parts. As shown by previous investigations, the toroidal field produces more than 90 % of the EM torque. It can be obtained by solving the associated (toroidal) induction equation for the electrically conducting part of the mantle, i.e. an initial boundary value problem (IBVP). The IBVP differs basically from that for the poloidal field by the boundary values at the interface between lower conducting and upper insulating parts of the mantle: the toroidal field vanishes, the poloidal field continues harmonically as potential field towards the Earth surface. The two major subjects are to find a suitable algorithm to solve the IBVP and to compute the toroidal geomagnetic field at the CMB. Compared to the poloidal field, the toroidal field at the CMB cannot be inferred from geomagnetic observations at the Earth's surface. In this study, it is inferred from the velocity field of the fluid core flow and the poloidal field at the CMB using an approximation which is consistent with the frozen-field approximation of the geomagnetic secular variation. This investigation differs from earlier ones by: (i) inferring the poloidal field at the CMB from the observed geomagnetic field using a rigorous inversion of the associated (poloidal) induction equation on which the fluid-flow inversion is based to determine consistently the surface flow velocities at the CMB, (ii) applying orthonormal spherical harmonic functions for the representation of the fields and torques, (iii) solving the IBVP numerically by a modified Crank-Nicolson algorithm, which (iv) allows us to highlight the influence of this approach on the resulting EM coupling torques. In addition to an outline of the derivations of the theoretical formalism and numerical methods, the time-variable toroidal field at the CMB is presented for different conductivity models.

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Axial poloidal electromagnetic core-mantle coupling torque: A re-examination for different conductivity and satellite supported geomagnetic field models

Cited by 4 publications

References 27 publications

Towards Understanding the Interconnection between Celestial Pole Motion and Earth’s Magnetic Field Using Space Geodetic Techniques

Towards Understanding the Interconnection between Celestial Pole Motion and Earth’s Magnetic Field Using Space Geodetic Techniques

The 1991 geomagnetic jerk as seen at the Earth's surface and the core-mantle boundary

Determining the time-variable part of the toroidal geomagnetic field in the core-mantle boundary zone

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