Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from <i>PKP</i>(BC)–<i>PKP</i>(DF) times

Tanaka, Satoru; Hamaguchi, Hiroyuki

doi:10.1029/96jb03187

Cited by 295 publications

(302 citation statements)

References 47 publications

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“…It is known from body wave studies that the heterogeneity at the top of the inner core has a strong s = 1 signal that is roughly divided into a western and an eastern hemisphere (Tanaka and Hamaguchi, 1997;Creager, 2000). The fact that isolated modes are insensitive to such structure does not affect the ability of a mode analysis to track down the differential rotation, provided the inner core rotates as a rigid body.…”

Section: Discussionmentioning

confidence: 99%

The Earth's free oscillations and the differential rotation of the inner core

Laske¹,

Masters²

2003

Earth's Core: Dynamics, Structure, Rotation

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Differential rotation of the inner core has been inferred by several body-wave studies with most agreeing that a superrotation may exist with a rate between 0.2 • and 3 • per year. The wide range of inferred rotation rate is caused by the sensitivity of such studies to local complexities in structure which have been demonstrated to exist. Freeoscillation "splitting functions" are insensitive to local structure and are therefore better candidates for estimating differential IC rotation more accurately. We use a recently developed method for analyzing free oscillations which is insensitive to earthquake source, location and mechanism to constrain this differential rotation. In a prior study, we found that inner core differential rotation has been essentially zero over the last 20 years. We revisit this issue, including additional earthquakes and modes in our analysis. Our best estimate is a barely significant superrotation of 0.13±0.11 • /yr, which is still consistent with the idea that the inner core is gravitationally locked to the mantle.

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Section: Discussionmentioning

confidence: 99%

The Earth's free oscillations and the differential rotation of the inner core

Laske¹,

Masters²

2003

Earth's Core: Dynamics, Structure, Rotation

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“…Aubert et al (2008a) suggest that at least the cyclones beneath Asia may reach down to the inner core and increases the removal of heat and light elements from it's eastern hemisphere. This could help to explain why seismic waves that pass through the top hundred 100 km of this hemisphere are faster, more isotropic, and more attenuated (Tanaka and Hamaguchi 1997;Niu and Wen 2001;Yu and Wen 2006). Laboratory experiments have shown that the inner-core growth rate influences the structure of the hexagonal-closed-pack (hcp) inner-core iron: slower iron solidification favors wider spaced and more oriented dendritic growth (Bergman 2003).…”

Section: Mantle Controlmentioning

confidence: 99%

Theory and Modeling of Planetary Dynamos

Wicht

Tilgner

2010

Space Sci Rev

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Numerical dynamo models are increasingly successful in modeling many features of the geomagnetic field. Moreover, they have proven to be a useful tool for understanding how the observations connect to the dynamo mechanism. More recently, dynamo simulations have also ventured to explain the surprising diversity of planetary fields found in our solar system. Here, we describe the underlying model equations, concentrating on the Boussinesq approximations, briefly discuss the numerical methods, and give an overview of existing model variations. We explain how the solutions depend on the model parameters and introduce the primary dynamo regimes. Of particular interest is the dependence on the Ekman number which is many orders of magnitude too large in the models for numerical reasons. We show that a minor change in the solution seems to happen at E = 3×10 −6 whose significance, however, needs to be explored in the future. We also review three topics that have been a focus of recent research: field reversal mechanisms, torsional oscillations, and the influence of Earth's thermal mantle structure on the dynamo. Finally we discuss the possibility of tidally or precession driven planetary dynamos.

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“…[2] One possibility for the hemispherical variations [Cao and Romanowicz, 2004;Niu and Wen, 2001;Tanaka and Hamaguchi, 1997] is that thermal variations in the lower mantle exert long term control over outer core convection, which then get recorded in the solidification texture of the inner core [Bergman et al, 2005;Aubert et al, 2008]. Another possibility, explored here, is that the inner core is translating eastward due to convection [Alboussiere et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

Grain growth and loss of texture during annealing of alloys, and the translation of Earth’s inner core

Bergman

Lewis

Myint

et al. 2010

Geophysical Research Letters

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The Earth's inner core is seismically anisotropic, with the direction parallel to the rotation axis both fast and more attenuating. There is also increasing evidence that the inner core is asymmetric, with the western hemisphere exhibiting slower direction‐averaged P wave velocity, less overall attenuation, and greater elastic anisotropy. It was recently suggested that the hemispherical variations might result from convective translation, whereby enhanced solidification in the western hemisphere leads to a net eastward translation of inner core material, with melting occurring in the east. Annealing accompanies this eastward movement. This study examines experimentally a previously unobserved sequence of grain growth and loss of texture during the annealing of a directionally solidified alloy. The growth of newly nucleated grains results because the original grains that resulted from directional solidification have a high energy associated with intragranular interphase boundaries, and because the minor element has a very low solubility in the primary phase so that a more traditional sequence of coarsening is not possible. This supplies a physical mechanism for the loss of texture that is suggested seismically.

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Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from PKP(BC)–PKP(DF) times

Cited by 295 publications

References 47 publications

The Earth's free oscillations and the differential rotation of the inner core

The Earth's free oscillations and the differential rotation of the inner core

Theory and Modeling of Planetary Dynamos

Grain growth and loss of texture during annealing of alloys, and the translation of Earth’s inner core

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