scholarly journals Rapid Variations of Earth’s Core Magnetic Field

2022 ◽  
Author(s):  
V. Lesur ◽  
N. Gillet ◽  
M. D. Hammer ◽  
M. Mandea
Keyword(s):  
Temporal Structure ◽  
Outer Core ◽  
Magnetic Observatory ◽  
Earth’S Core ◽  
Earth's Core ◽  
Core Mantle Boundary ◽  
Core Field ◽  
The Core ◽  
Global Modelling ◽  
Spatio Temporal

AbstractEvidence of fast variations in the Earth’s core field are seen both in magnetic observatory and satellite records. We present here how they have been identified at the Earth’s surface from ground-based observatory records and how their spatio-temporal structure is now characterised by satellite data. It is shown how their properties at the core mantle boundary are extracted through localised and global modelling processes, paying particular attention to their time scales. Finally are listed possible types of waves in the liquid outer core, together with their main properties, that may give rise to these observed fast variations.

scholarly journals Thermal conductivity of Fe-Si alloys and thermal stratification in Earth’s core

2021 ◽  
Vol 119 (1) ◽  
pp. e2119001119
Author(s):  
Youjun Zhang ◽  
Kai Luo ◽  
Mingqiang Hou ◽  
Peter Driscoll ◽  
Nilesh P. Salke ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Pressure ◽  
Transport Properties ◽  
Outer Core ◽  
Earth’S Core ◽  
High Pressure And Temperature ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core

Light elements in Earth’s core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron–electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m−1⋅K−1 for liquid Fe-9Si near the topmost outer core. If Earth’s core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core–mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core–mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.

scholarly journals Reflection and transmission of seismic waves under initial stress at the earth's core-mantle boundary

1980 ◽  
Vol 3 (3) ◽  
pp. 591-598
Author(s):  
Sukhendu Dey ◽  
Sushil Kumar Addy
Keyword(s):  
Initial Stress ◽  
Seismic Waves ◽  
Reflection And Transmission Coefficients ◽  
Earth’S Core ◽  
Reflection And Transmission ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Transmission Coefficients ◽  
The Core

In the present paper the influence of the initial stress is shown on the reflection and transmission ofPwaves at the core-mantle boundary. Taking a particular value of the inherent initial stress, the variations of reflection and transmission coefficients with respect to the angle of emergence are represented by graphs. These graphs when compared with those having no initial stress show that the effect of the initial stress is to produce a reflectedPandSwaves with numerically higher amplitudes but a transmittedPwave with smaller amplitude. A method is also indicated in this paper to calculate the actual value of the initial stress near the core-mantle boundary by measuring the amplitudes of incident and reflectedPwaves.

Thermodynamics from first principles: temperature and composition of the Earth’s core

2003 ◽  
Vol 67 (1) ◽  
pp. 113-123 ◽  
Author(s):  
D. Alfé ◽  
M. J. Gillan ◽  
G. D. Price
Keyword(s):  
Melting Temperature ◽  
First Principles ◽  
Inner Core ◽  
Melting Curve ◽  
Outer Core ◽  
Earth’S Core ◽  
Earth's Core ◽  
The Core ◽  
Core Conditions ◽  
Main Ideas

AbstractWe summarize the main ideas used to determine the thermodynamic properties of pure systems and binary alloys from first principles calculations. These are based on the ab initio calculations of free energies. As an application we present the study of iron and iron alloys under Earth,s core conditions. In particular, we report the whole melting curve of iron under these conditions, and we put constraints on the composition of the core. We found that iron melts at 6350士600 K at the pressure corresponding to the boundary between the solid inner core and the liquid outer core (ICB). We show that the core could not have been formed from a binary mixture of Fe with S, Si or O and we propose a ternary or quaternary mixture with 8—10% of S/Si in both liquid and solid and an additional ~8% of oxygen in the liquid. Based on this proposed composition we calculate the shift of melting temperature with respect to the melting temperature of pure Fe of ~—700 K, so that our best estimate for the temperature of the Earth's core at ICB is 5650±600 K.

Melting of iron–silicon alloy up to the core–mantle boundary pressure: implications to the thermal structure of the Earth’s core

2009 ◽  
Vol 37 (6) ◽  
pp. 353-359 ◽  
Author(s):  
Hidetoshi Asanuma ◽  
Eiji Ohtani ◽  
Takeshi Sakai ◽  
Hidenori Terasaki ◽  
Seiji Kamada ◽  
...  
Keyword(s):  
Thermal Structure ◽  
Earth’S Core ◽  
Earth's Core ◽  
Silicon Alloy ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Iron Silicon ◽  
The Core

scholarly journals Experimental evidence for hydrogen incorporation into Earth’s core

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shoh Tagawa ◽  
Naoya Sakamoto ◽  
Kei Hirose ◽  
Shunpei Yokoo ◽  
John Hernlund ◽  
...  
Keyword(s):  
Terrestrial Planet ◽  
Outer Core ◽  
Core Formation ◽  
Earth’S Core ◽  
Hydrogen Incorporation ◽  
Earth's Core ◽  
The Core ◽  
The Earth ◽  
Metal Silicate ◽  
Important Constituent

AbstractHydrogen is one of the possible alloying elements in the Earth’s core, but its siderophile (iron-loving) nature is debated. Here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30–60 gigapascals and 3100–4600 kelvin. We find that hydrogen has a metal/silicate partition coefficient DH ≥ 29 and is therefore strongly siderophile at conditions of core formation. Unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3–0.6 wt% H was incorporated into the core, leaving a relatively small residual H2O concentration in silicates. This amount of H explains 30–60% of the density deficit and sound velocity excess of the outer core relative to pure iron. Our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of ~10% of the Earth.

scholarly journals Possible Changes in the Core-Mantle and Inner-Outer Core Boundaries

1972 ◽  
Vol 48 ◽  
pp. 179-181
Author(s):  
J. A. Jacobs
Keyword(s):  
Outer Core ◽  
Temporal Changes ◽  
Time Intervals ◽  
Earth’S Core ◽  
Earth's Core ◽  
Size And Shape ◽  
The Core ◽  
Earth’S Mantle ◽  
Short Time

This paper investigates the possibility that the boundaries between the Earth's mantle and core and between the inner and outer core might show temporal changes. The evolution of the Earth's core is not discussed, but the question is raised as to whether these boundaries might not undergo small changes both in size and shape over comparatively short time intervals.

The fine structure of the Earth's core

1964 ◽  
Vol 54 (5A) ◽  
pp. 1299-1313 ◽  
Author(s):  
R. D. Adams ◽  
M. J. Randall
Keyword(s):  
Fine Structure ◽  
Travel Time ◽  
Velocity Gradient ◽  
Inner Core ◽  
Outer Core ◽  
Earth’S Core ◽  
Time Curve ◽  
Earth's Core ◽  
The Core

Abstract Detailed study of arrivals from accurately fixed earthquakes has revealed additional complexity in the travel-time curve for PKP. A notation is introduced in which observations are denoted by P′ with a two-letter suffix indicating the branch to which they belong, namely P′AB, P′IJ, P′GH and P′DF. A new velocity solution for the Earth's core has been derived from these observations. This velocity solution differs from those previously suggested in having three discontinuous increases in velocity between the outer and inner core, at levels corresponding to 0.570, 0.455 and 0.362 times the radius of the core. This implies two shells, each between 300 and 400 km thick, surrounding the inner core; in each shell there is a small negative velocity gradient. The outer discontinuity is sufficiently shallow to prevent rays in the outer core from forming a caustic.

scholarly journals Applications for CryoSat-2 satellite magnetic data in studies of Earth’s core field variations

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Magnus D. Hammer ◽  
Christopher C. Finlay ◽  
Nils Olsen
Keyword(s):  
Spatial Resolution ◽  
Spherical Harmonic ◽  
Earth’S Core ◽  
Spherical Harmonic Degree ◽  
Earth's Core ◽  
Core Field ◽  
The Core ◽  
Low Latitudes ◽  
Magnetometer Data ◽  
Harmonic Degree

AbstractWe use 20 years of continuous magnetic field measurements from the Ørsted, CHAMP and Swarm satellite missions, supplemented by calibrated platform magnetometer data from the CryoSat-2 satellite, to study time variations of the Earth’s core field at satellite altitude and at the core–mantle boundary (CMB). From the satellite data we derive composite time series of the core field secular variation (SV) with 4-month cadence, at 300 globally distributed Geomagnetic Virtual Observatories (GVO). A previous gap in the GVO series between 2010 and 2014 is successfully filled using CryoSat-2, and sub-decadal variations are identified during this period. Tests showed that similar sub-decadal SV patterns were obtained from the CryoSat-2 data regardless of whether IGRF-13 or CHAOS-6x9 was used in their calibration. Cryosat-2 radial field SV series at non-polar latitudes have a mean standard deviation level compared to smoothing spline fits of 3.5 nT/yr compared to 1.8 nT/yr for CHAMP and 0.9 nT/yr for Swarm. GVO radial SV series display regional fluctuations with 5–10 years duration and amplitudes reaching 20 nT/yr, most notably at low latitudes over Indonesia (2014), over South America and the South Atlantic (2007, 2011 and 2014), and over the central Pacific (2017). Applying the Subtractive Optimally Localized Averages (SOLA) method, we also map the radial SV at the CMB as a collection of locally averaged SV estimates. We demonstrate that using 2-year windows of CryoSat-2 data, it is possible to reliably estimate the SV and its time derivative, the secular acceleration (SA), at the CMB, with a spatial resolution, corresponding to spherical harmonic degree 10. Along the CMB geographic equator, we find strong SA features with amplitude $$\pm 2.5\mu \mathrm{T}/\mathrm{yr}^2$$ ± 2.5 μ T / yr 2 under Indonesia from 2011–2014, under central America from 2015 to 2019, and sequences of SA with alternating sign under the Atlantic during 2004–2019. We find that platform magnetometer data from CryoSat-2 make a valuable contribution to the emerging picture of sub-decadal core field variations. Using 1-year windows of data from the Swarm satellites, we show that it is possible to study SA changes at low latitudes on timescales down to 1 year, with spatial resolution corresponding to spherical harmonic degree 10. We find strong positive and negative SA features appearing side-by-side in the Pacific in 2017, and thereafter drift westward.

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