Geomagnetic jerks from the Earth’s surface to the top of the core

Chambodut, Aude; Eymin, Céline; Mandéa, Mioara

doi:10.1186/bf03352730

Cited by 12 publications

(11 citation statements)

References 54 publications

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“…More surprising are the results obtained for 1991, where the dates seem to indicate a change in occurrence tendency, with an early occurrence in a "European/African" region; however, this result must be carefully considered, due to the more complicated 1991 jerk structure. The CM4 model also suggests a sudden event in 1985, striking because it might not be worldwide in occurrence, but localized mainly in the Pacific area (Chambodut et al 2007).…”

Section: Geomagnetic Jerks Detected By Geomagnetic Modelsmentioning

confidence: 99%

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

et al. 2010

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The secular variation of the core field is generally characterized by smooth variations, sometimes interrupted by abrupt changes, named geomagnetic jerks. The origin of these events, observed and investigated for over three decades, is still not fully understood. Many fundamental features of geomagnetic jerks have been the subject of debate, including their origin internal or external to the Earth, their occurrence dates, their duration and their global or regional character. Specific tools have been developed to detect them in geomagnetic field or secular variation time series. Recently, their investigation has been advanced by the availability of a decade of high-quality satellite measurements. Moreover, advances in the modelling of the core field and its variations have brought new perspectives on the fluid motion at the top of the core, and opened new avenues in our search for the origin of M. Mandea ( ) Helmholtz-Zentrum

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Section: Geomagnetic Jerks Detected By Geomagnetic Modelsmentioning

confidence: 99%

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

et al. 2010

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“…In addition, there is ongoing discussion about the jerk-generating processes in the outer core and the existence of stably stratified layer in the liquid outer core below the CMB (e.g. Dormy & Mandea 2005;Chambodut et al 2007;Olsen et al 2010;Davies & Gubbins 2011). Moreover, different approaches have been published to describe the spatial structure of the appearance of jerks on the Earth's surface, or at satellite altitudes (e.g.…”

Section: Introductionmentioning

confidence: 99%

The adjoint-state method for the downward continuation of the geomagnetic field

Hagedoorn

Martinec

2015

Geophysical Journal International

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S U M M A R YThe downward continuation of the observed geomagnetic field from the Earth's surface to the core-mantle boundary (CMB) is complicated due to induction and diffusion processes in the electrically conducting Earth mantle, which modify the amplitudes and morphology of the geomagnetic field. Various methods have been developed to solve this problem, for example, the perturbation approach by Benton & Whaler, or the non-harmonic downward continuation by Ballani et al.In this paper, we present a new approach for determining the geomagnetic field at the CMB by reformulating the ill-posed, one-sided boundary-value problem with time-variable boundary-value function on the Earth's surface into an optimization problem for the boundary condition at the CMB. The reformulated well-posed problem is solved by a conjugate gradient technique using the adjoint gradient of a misfit. For this purpose, we formulate the geomagnetic adjoint-state equations for efficient computations of the misfit gradient. Beside the theoretical description of the new adjoint-state method (ASM), the first applications to a global geomagnetic field model are presented. The comparison with other methods demonstrates the capability of the new method to determine the geomagnetic field at the CMB and allows us to investigate the variability of the determined field with respect to the applied methods. This shows that it is necessary to apply the ASM when investigating the effect of the Earth's mantle conductivity because the difference between the results of approximate methods (harmonic downward continuation, perturbation approach) and the rigorous ASM are of the same order as the difference between the results of the ASM applied for different mantle conductivities.

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“… Several studies have linked the occurrence of geomagnetic jerks to processes in the liquid outer core or on its surface (Davis & Whaler 1997; Le Huy et al 1998, 2000; Bellanger et al 2001; Bloxham et al 2002; Holme & de Viron 2005; Chambodut et al 2007; Olsen & Mandea 2008; Wardinski et al 2008). The influence of the mantle conductivity on jerks or conductivity estimates by jerk data were considered from the beginning (Achache et al 1980; Ducruix et al 1980; Backus 1983; Courtillot et al 1984; Mandea‐Alexandrescu et al 1999; Nagao et al 2003; Pinheiro & Jackson 2008).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

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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Geomagnetic jerks from the Earth’s surface to the top of the core

Cited by 12 publications

References 54 publications

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

The adjoint-state method for the downward continuation of the geomagnetic field

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

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