scholarly journals Reexamination of Fluid Motion in the Earth's Core Derived from Geomagnetic Field Data. Is the .OMEGA.-Effect Really Strong in the Core?

1992 ◽  
Vol 44 (7) ◽  
pp. 521-553 ◽  
Author(s):  
Masaki MATSUSHIMA ◽  
Yoshimori HONKURA
Keyword(s):  
Geomagnetic Field ◽  
Field Data ◽  
Fluid Motion ◽  
Earth’S Core ◽  
Earth's Core ◽  
The Core

Dynamics of a fluid core with inward growing boundaries

1980 ◽  
Vol 17 (1) ◽  
pp. 72-89 ◽  
Author(s):  
H. H. Schloessin ◽  
J. A. Jacobs
Keyword(s):  
Lower Mantle ◽  
Solid Phase ◽  
Fluid Motion ◽  
Density Currents ◽  
Phase Growth ◽  
Earth’S Core ◽  
Earth's Core ◽  
The Core ◽  
Fluid Core ◽  
Solid Phases

In both physical and mathematical models of the Earth's core it has been difficult, so far, to discuss all the terms in the magneto-hydrodynamic energy equation under one unifying theory and to relate all the physical mechanisms involved in a specific model. The reason for this is mainly the uncertainty about the energy sources, or, when they could be accounted for, with uncertainty about their location. In the following article we deduce and examine a model of the Earth's core which can be regarded as a sequel to theories of the formation of a fluid core in the course of the Earth's thermal evolution.General cooling and pressure-freezing cause the formation of solid phases at the boundaries of the fluid core, leading to a solid inner core (IC) and a lower mantle shell (Bullen's D″ layer) from slow overgrowth at the mantle–core (MC) boundary. For simplicity, the core fluid is assumed to consist of two major phases, one conducive to solid metallic core formation, and the other to crystallization of a lower mantle phase from "solution" in a metal "solvent." The presence of a third, minor constituent, by selective partitioning between phases, acts as a solid phase growth regulator.On the basis of this model the energy available for fluid core motion and thereby for maintenance of the magnetic field, is related directly to the time rate of change of the growth of the solid phases at the IC and MC boundaries. Most of the available energy is gravitational and is associated with density and concentration currents which offset density inhomogeneities caused by selective acceptance and rejection of the fluid core constituents by the two solid phases.A very conservative estimate of the net gain per second in gravitational potential energy resulting from the mass redistribution via density currents and solid phase formation is 2.6 × 1013 W which may become available in different forms. The fraction which is converted into kinetic energy associated with differential circulatory motion around the rotation axis amounts to 3.4 × 1011 W, based on radial interchange with respect to the Earth's centre. The heat liberated as a result of IC solidification is 2.7 × 1011 W, assuming that the metallic phase is mainly iron. Since our ideas of other constituents of the core fluid are less definite we can draw only very general conclusions about the MC boundary. If silicates and oxides are likely candidates, it is possible that in the crystallization of the mantle phase from the core fluid, heat is being absorbed, thus creating a heat sink at the MC boundary. An estimate of the net strain energy associated with compression of IC material by about 1.4% and expansion of MC material by, on the average, 0.4% gives 1.5 × 1011 W.Magnetic polarity reversals might be explained as due to epochs during which the solid phase growth rate which dominates the fluid motion shifts from the IC to the MC boundary and vice versa. Intensity changes might be due to significant variations in the ratio of the radial and horizontal velocity components of the fluid motion.

scholarly journals Nonlinear MHD Rossby wave interactions and persistent geomagnetic field structures

2020 ◽  
Vol 476 (2241) ◽  
pp. 20200174
Author(s):  
Breno Raphaldini ◽  
Carlos F. M. Raupp
Keyword(s):  
Nonlinear Interaction ◽  
Geomagnetic Field ◽  
Stationary Flow ◽  
Stationary Waves ◽  
Wave Interactions ◽  
Earth’S Core ◽  
Meridional Component ◽  
Earth's Core ◽  
The Core ◽  
Core Dynamics

The geomagnetic field presents several stationary features that are thought to be linked to inhomogeneities at the core–mantle boundary. Particularly important stationary structures of the geomagnetic field are the flux lobes, which appear in pairs in mid- to high mid- to high latitudes. A recently discovered stratified layer at the top of the Earth’s core poses important constraints on the dynamics at this layer and on the interaction of the core dynamics and the base of the mantle. In this article, we introduce the linear and nonlinear theories of magnetic Rossby waves in a thin shell at the top of the Earth’s core. We study the nonlinear interaction of these waves in the presence of prescribed forcings at the base of the mantle of both a thermal and a topographic nature. We show that the combined effects of forcing and nonlinear interaction can lead the wave phases to be locked around a particular geographical longitude, generating a quasi- stationary flow pattern with a significant meridional component. The solutions of the system are shown to be analogous to atmospheric blocking phenomena. Therefore, we argue that persistent and long-lived structures of the geomagnetic field, such as the geomagnetic lobes, might be associated with a blocking at the top of the Earth’s core due to nonlinear stationary waves.

scholarly journals Recent geomagnetic variations and the force balance in Earth’s core

2020 ◽  
Vol 221 (1) ◽  
pp. 378-393 ◽  
Author(s):  
Julien Aubert
Keyword(s):  
Geomagnetic Field ◽  
General Circulation ◽  
Force Balance ◽  
Leading Order ◽  
Earth’S Core ◽  
Geomagnetic Variations ◽  
Earth's Core ◽  
The Core ◽  
Model Interpretation ◽  
Geomagnetic Data

SUMMARY The nature of the force balance that governs the geodynamo is debated. Recent theoretical analyses and numerical simulations support a quasigeotrophic (QG), magneto-Archimedes-Coriolis (MAC) balance in Earth’s core, where the Coriolis and pressure forces equilibrate at leading order in amplitude, and where the buoyancy, Lorentz and ageostrophic Coriolis forces equilibrate at the next order. In contrast, earlier theoretical expectations have favoured a magnetostrophic regime where the Lorentz force would reach leading order at the system scale. The dominant driver (buoyant or magnetic) for the general circulation in Earth’s core is equally debated. In this study, these questions are explored in the light of the high-quality geomagnetic data recently acquired by satellites and at magnetic ground observatories. The analysis involves inverse geodynamo modelling, a method that uses multivariate statistics extracted from a numerical geodynamo model to infer the state of Earth’s core from a geomagnetic field model interpretation of the main field and secular variation data. To test the QG-MAC dynamic hypothesis against the data, the framework is extended in order to explicitly prescribe this force balance into the inverse problem solved at the core surface. The resulting inverse solutions achieve a quantitatively adequate fit to the data while ensuring deviations from the QG-MAC balance (which amount to an inertial driving of the flow) lower than each of the leading forces. The general circulation imaged within the core over the past two decades confirms the existence of a planetary-scale, eccentric, axially columnar gyre that comprises an intense, equatorially symmetric jet at high latitudes in the Pacific hemisphere. The dominant driver of this circulation is shown to be of buoyant nature, through a thermal wind balance with a longitudinally hemispheric buoyancy anomaly distribution. Geomagnetic forecasts initiated with the inverted core states are systematically more accurate against the true interannual geomagnetic field evolution when enforcing the QG-MAC constraint. This force balance is therefore consistent with the geomagnetic data at the large scales of Earth’s core that can be imaged by the method.

scholarly journals Wave velocities in the earth's core

1958 ◽  
Vol 48 (4) ◽  
pp. 301-314
Author(s):  
B. Gutenberg
Keyword(s):  
Travel Time ◽  
Transition Zone ◽  
Southern California ◽  
Inner Core ◽  
Travel Times ◽  
Earth’S Core ◽  
Earth's Core ◽  
The Core ◽  
Wave Velocities

Abstract More than 700 seismograms of 39 shocks recorded mainly in southern California at epicentral distances between 105 and 140 degrees are used to investigate records of phases which have penetrated the earth's core. Properties of PKIKP, SKP, SKIKP, PKS, and PKIKS are discussed. Portions of travel-time curves of these phases are revised. Travel times of waves starting and ending at the surface of the core, and wave velocities in the core, are recalculated. Between about 1,500 and 1,200 km. from the earth's center in the transition zone from the liquid outer to the probably solid inner core, waves having lengths of the order of 10 km. travel faster than longer waves. This is probably caused by a rather rapid increase in viscosity toward the earth's center in this transition zone.

The chemical composition of the Earth's core: Possibility of sulphur in the core

1970 ◽  
Vol 2 (4) ◽  
pp. 276-282 ◽  
Author(s):  
V. Rama Murthy ◽  
H.T. Hall
Keyword(s):  
Chemical Composition ◽  
Earth’S Core ◽  
Earth's Core ◽  
The Core

scholarly journals Using symbolic calculations to calculate the eigenmodes of the free damping of a geomagnetic field

2018 ◽  
Vol 62 ◽  
pp. 02018 ◽  
Author(s):  
Gleb Vodinchar
Keyword(s):  
Geomagnetic Field ◽  
Earth’S Core ◽  
Earth's Core ◽  
Symbolic Computations ◽  
Damped Oscillations ◽  
Symbolic Calculations

The method for calculating the eigenmodes of free damped oscillations of the geomagnetic field in the Earth’s core using symbolic computations is described.

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

1986 ◽  
Vol 91 (B12) ◽  
pp. 12444-12466 ◽  
Author(s):  
Coerte V. Voorhies
Keyword(s):  
Geomagnetic Field ◽  
Steady Flows ◽  
Earth’S Core ◽  
Earth's Core ◽  
Geomagnetic Field Models

Motions of the Earth's Core and Mantle, and Variations of the Main Geomagnetic Field

Science ◽  
1967 ◽  
Vol 157 (3784) ◽  
pp. 55-56 ◽  
Author(s):  
R. Hide
Keyword(s):  
Geomagnetic Field ◽  
Earth’S Core ◽  
Earth's Core
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