scholarly journals New Determination of the “Decade” Fluctuations in the Rotation of the Earth 1860–1978

1979 ◽  
Vol 82 ◽  
pp. 55-57
Author(s):  
L. V. Morrison
Keyword(s):  
Angular Momentum ◽  
Electromagnetic Coupling ◽  
Viscous Stress ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Topographic Features ◽  
The Core ◽  
The Earth ◽  
Rotation Of The Earth

Observations of the Earth's rotation have shown irregular variations of rate which have characteristic times of decades. These have been attributed to transfer of angular momentum between core and mantle by some mechanism such as inertial coupling, viscous stress, electromagnetic coupling or stresses produced by topographic features on the core mantle boundary.

Addendum 2020 to ‘Measurement of the Earth’s rotation: 720 BC to AD 2015’

2021 ◽  
Vol 477 (2246) ◽  
pp. 20200776
Author(s):  
L. V. Morrison ◽  
F. R. Stephenson ◽  
C. Y. Hohenkerk ◽  
M. Zawilski
Keyword(s):  
Angular Momentum ◽  
Earth’S Rotation ◽  
The Sun ◽  
Earth's Rotation ◽  
Moon System ◽  
Link Type ◽  
The Earth ◽  
Solar Eclipses ◽  
Rotation Of The Earth

Historical reports of solar eclipses are added to our previous dataset (Stephenson et al. 2016 Proc. R. Soc. A 472 , 20160404 ( doi:10.1098/rspa.2016.0404 )) in order to refine our determination of centennial and longer-term changes since 720 BC in the rate of rotation of the Earth. The revised observed deceleration is −4.59 ± 0.08 × 10 −22  rad s −2 . By comparison the predicted tidal deceleration based on the conservation of angular momentum in the Sun–Earth–Moon system is −6.39 ± 0.03 × 10 −22  rad s −2 . These signify a mean accelerative component of +1.8 ± 0.1 × 10 −22  rad s −2 . There is also evidence of an oscillatory variation in the rate with a period of about 14 centuries.

Problems related to PcP and the core-mantle boundary illustrated by two nuclear events

1973 ◽  
Vol 63 (6-1) ◽  
pp. 2047-2070 ◽  
Author(s):  
Goetz G. R. Buchbinder ◽  
Georges Poupinet
Keyword(s):  
Inner Core ◽  
Wave Form ◽  
Model Parameters ◽  
Travel Times ◽  
P Waves ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Order Of Magnitude

Abstract Two large nuclear explosions produced a considerable number of PcP phases. Analysis of the P and PcP travel times shows a scatter of ±2 sec. It is pointed out that PcP and P times must be considered together to eliminate gross upper mantle effects on the travel times. On a worldwide basis, the PcP peak-to-peak amplitudes exhibit a scatter of up to one order of magnitude, and, thus, the reflection coefficient of the core-mantle boundary (cmb) may not be determined with any significance from them. Comparing the wave form of PcP and the wave form of P waves convolved with thin-layered models of the cmb suggests that the cmb may be approximated by a thin high-impedance liquid layer of several kilometers in thickness embedded between the mantle and the core. Such a model can explain observed dilatational arrivals and a small decrease in amplitude near Δ ≈ 30°. The data do not permit exact determination of the model parameters because of uncertainty in the data and insensitivity of the method and because the cmb also may be laterally inhomogeneous. The frequency-dependence of the reflection and transmission coefficients of a layered cmb would have serious effects on the determination of inner core parameters.

GRACEFUL: Probing the deep Earth interior by synergistic use of observations of the magnetic and gravity fields, and of the rotation of the Earth

2020 ◽  
Author(s):  
Mioara Mandea ◽  
Veronique Dehant ◽  
Anny Cazenave
Keyword(s):  
Magnetic Field ◽  
Gravity Field ◽  
Time Scales ◽  
Earth Rotation ◽  
Outer Core ◽  
Time Dependent ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
The Earth

<div> <p>To understand the processes involved in the deep interior of the Earth and explaining its evolution, in particular the dynamics of the Earth’s fluid iron-rich outer core, only indirect satellite and ground observations are available. They each provide invaluable information about the core flow but are incomplete on their own:</p> <p>-        The time dependent magnetic field, originating mainly within the core, can be used to infer the motions of the fluid at the top of the core on decadal and subdecadal time scales.</p> <p>-        The time dependent gravity field variations that reflect changes in the mass distribution within the Earth and at its surface occur on a broad range of time scales. Decadal and interannual variations include the signature of the flow inside the core, though they are largely dominated by surface contributions related to the global water cycle and climate-driven land ice loss.</p> <p>-        Earth rotation changes (or variations in the length of the day) also occur on these time scales, and are largely related to the core fluid motions through exchange of angular momentum between the core and the mantle at the core-mantle boundary.</p> <p>Here, we present the main activities proposed in the frame of the GRACEFUL ERC project, which aims to combine information about the core deduced from the gravity field, from the magnetic field and from the Earth rotation in synergy, in order to examine in unprecedented depth the dynamical processes occurring inside the core and at the core-mantle boundary.</p> </div>

scholarly journals Can the Core-Mantle Boundary Topography Influence the Earth's Nutation?

1990 ◽  
Vol 141 ◽  
pp. 161-162
Author(s):  
V. V. Bykova
Keyword(s):  
Perturbation Theory ◽  
Liquid Core ◽  
Theory Method ◽  
Mantle Boundary ◽  
First Order ◽  
Core Mantle Boundary ◽  
The Core ◽  
The Earth ◽  
Annual Term ◽  
Boundary Form

The nutation of the Earth with slightly nonelliptical liquid core is investigated by the perturbation theory method. It is shown that first-order terms affect the core ellipticity and its triaxiality. The most sensitive nutation terms in the second approximation were found to be retrograde 18.6-year term and retrograde annual term. The observed nutation amplitude values can be satisfied by special core-mantle boundary form.

scholarly journals Properties of the Core-Mantle Boundary

1988 ◽  
Vol 129 ◽  
pp. 377-377
Author(s):  
Bradford H. Hager
Keyword(s):  
Mechanical Properties ◽  
Thermal Boundary Layer ◽  
Seismic Velocity ◽  
Velocity Versus ◽  
Compositional Gradient ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
The Earth ◽  
Thick Region

The core-mantle boundary (CMB), separating the molten metallic core from the overlying solid silicate mantle, marks the largest discontinuity in mechanical properties within the Earth. The ∼ 200 km thick region just above the CMB, named D″ by Bullen (1950), is characterized by an anomalous gradient in seismic velocity versus depth. D″ was originally interpreted as a region with a strong compositional gradient due to the accumulation of dense material at the base of the mantle. Subsequently, the anomalous gradient was interpreted as the result of a strong temperature gradient in a hot thermal boundary layer at the base of the mantle, an interpretation motivated by the requiremnet that heat involved in generating the geodynamo must be transported out of the core and through the mantle by convection.

scholarly journals GRACE—Gravity Data for Understanding the Deep Earth’s Interior

2020 ◽  
Vol 12 (24) ◽  
pp. 4186
Author(s):  
Mioara Mandea ◽  
Véronique Dehant ◽  
Anny Cazenave
Keyword(s):  
Gravity Data ◽  
Outer Core ◽  
Space Mission ◽  
Last Deglaciation ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Isostatic Adjustment ◽  
The Earth ◽  
Fluid Core

While the main causes of the temporal gravity variations observed by the Gravity Recovery and Climate Experiment (GRACE) space mission result from water mass redistributions occurring at the surface of the Earth in response to climatic and anthropogenic forces (e.g., changes in land hydrology, ocean mass, and mass of glaciers and ice sheets), solid Earth’s mass redistributions were also recorded by these observations. This is the case, in particular, for the glacial isostatic adjustment (GIA) or the viscous response of the mantle to the last deglaciation. However, it has only recently been shown that the gravity data also contain the signature of flows inside the outer core and their effects on the core–mantle boundary (CMB). Detecting deep Earth’s processes in GRACE observations offers an exciting opportunity to provide additional insight into the dynamics of the core–mantle interface. Here, we present one aspect of the GRACEFUL (GRavimetry, mAgnetism and CorE Flow) project, i.e., the possibility to use gravity field data for understanding the dynamic processes inside the fluid core and core–mantle boundary of the Earth, beside that offered by the geomagnetic field variations.

Commission 19: Rotation of the Earth (Rotation De La Terre)

1988 ◽  
Vol 20 (1) ◽  
pp. 179-194
Author(s):  
W. J Klepczynski ◽  
M. Feissel ◽  
B. Kolaczek ◽  
F. E Barlier ◽  
P. Brosche ◽  
...  
Keyword(s):  
Rotation Rate ◽  
Earth Rotation ◽  
Earth’S Rotation ◽  
International Earth Rotation Service ◽  
Earth's Rotation ◽  
Core Mantle Boundary ◽  
The Core ◽  
The Earth ◽  
Rotation Of The Earth ◽  
Observing Techniques

During the period, there have been several major events which have effected the scope and interest of Commission 19. The most significant of these has been the dissolution of the BIH and IPMS and their replacement by the International Earth Rotation Service (IERS). The correlation of higher frequency fluctuations in the Earth’s rotation rate with changes in the Earth’s Atmospheric Angular Momentum is also significant. Many investigators now seem to believe that the “decade variations„ in the Earth’s rotation rate are caused by torques between the core and mantle caused by the uneven motions at the core-mantle boundary. These events and discoveries have made this an exciting period. It seems that the future holds more in the way of discovery due to the utilization of the more accurate and precise Earth rotation data coming from the modern observing techniques.

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