Study of the Earth rheological properties from polar motion

2020 ◽  
Author(s):  
Christian Bizouard ◽  
Ibnu Nurul Huda ◽  
Sébastien Lambert
Keyword(s):  
Rheological Properties ◽  
Solid Earth ◽  
Polar Motion ◽  
Inner Core ◽  
Dynamical Behavior ◽  
Chandler Wobble ◽  
Love Number ◽  
Resonance Parameters ◽  
Global Circulation Models ◽  
The Earth

<pre>Since the beginning of the 20th century, the observation of the Earth rotation variations through astro-geodetic <br />techniques enables to investigate the global rheological properties of the Earth, in particular, the resonance <br />parameters of the free rotation modes reflect the solid Earth anelasticity, the ocean response to an external <br />forcing, and the properties of the fluid inner core, eventually of the solid inner core. Better constraints on <br />these resonance parameters can be obtained by confronting the observed terrestrial motion of the rotation pole <br />(the so-called polar motion) - including nutation as a retrograde diurnal polar motion - to the modeled excitation <br />producing it. The more precise the modeled excitation and the observed polar motion are, the better the<br />Earth rheological properties will be determined. For now, the best precision is reached in the<br />nutation band. So, the analysis has been first dedicated to a direct adjustment of the nutation components<br />from VLBI delays, then the adjustment of the resonance parameters in the transfer function between the observed <br />nutation terms and the corresponding rigid nutation terms that reflects the luni-solar forcing. The obtained <br />resonance parameters confirms in particular the shortening of the polar motion resonance period of about 40 - 50 day <br />in the retrograde diurnal band. Then, we show that the dynamical behavior of the oceans in the diurnal band is <br />mostly responsible for that. We also predicted a supplementary change of the resonance parameters in the vicinity<br />of the free core nutation resonance, as expected from the solid Earth response, and confirmed by the adjustment of <br />these parameters through the nutation terms. In addition to the nutation band, we revisit the estimation of the <br />polar motion resonance parameters in the seasonal band, dominated by the Chandler wobble, in light of the most <br />recent global circulation models of the hydro-atmospheric layers. Finally, we extend the investigation of polar motion resonance to the<br />prograde diurnal polar motion, where the excitations mostly result from the ocean tides. We obtain a resonance <br />period of about 393 days, and confirmed by our prediction based on the ocean tidal models. These results allow us to <br />impose constraints on the frequency dependence of the Love number k<sub>2</sub> and the Love number oceanic k<sub>o</sub>, characterizing <br />respectively the response of the solid Earth and the oceans to an external potential of degree 2. </pre>

Nutation terms adjustment to VLBI and implication for the Earth rotation resonance parameters

2019 ◽  
Vol 220 (2) ◽  
pp. 759-767 ◽  
Author(s):  
I Nurul Huda ◽  
S Lambert ◽  
C Bizouard ◽  
Y Ziegler
Keyword(s):  
Polar Motion ◽  
Inner Core ◽  
Resonance Parameters ◽  
Free Core Nutation ◽  
Long Baseline ◽  
The Earth ◽  
Significant Difference ◽  
Tidal Correction ◽  
Global Parameters

SUMMARY The nutation harmonic terms are commonly determined from celestial pole offset series produced from very long baseline interferometry (VLBI) time delay analysis. This approach is called an indirect approach. As VLBI observations are treated independently for every session, this approach has some deficiencies such as a lack of consistency in the geometry of the session. To tackle this problem, we propose to directly estimate nutation terms from the whole set of VLBI time delays, hereafter referred as a direct approach, in which the nutation amplitudes are taken as global parameters. This approach allows us to reduce the correlations and the formal errors and gives significant discrepancies for the amplitude of some nutation terms. This paper is also dedicated to the determination of the Earth resonance parameters, named polar motion, free core nutation, and free inner core nutation. No statistically significant difference has been found between the estimates of resonance parameters based upon ‘direct’ and ‘indirect’ nutation terms. The inclusion of a complete atmospheric-oceanic non-tidal correction to the nutation amplitudes significantly affected the estimates of the free core nutation and the free inner core nutation resonant frequencies. Finally, we analyzed the frequency sensitivity of polar motion resonance and found that this resonance is mostly determined by the prograde nutation terms of period smaller than 386 d.

scholarly journals Excitation of the Chandler Wobble

2000 ◽  
Vol 178 ◽  
pp. 455-462
Author(s):  
N.S. Sidorenkov
Keyword(s):  
Polar Motion ◽  
Southern Oscillation ◽  
World Ocean ◽  
Noise Spectrum ◽  
Chandler Wobble ◽  
The Earth ◽  
The Pacific ◽  
And Shifts ◽  
Chandler Period ◽  
Earth’S Inertia Tensor

AbstractThe redistribution of air and water masses between the Pacific and Indian oceans during the El Niño/Southern oscillation (ENSO) changes the components of the Earth’s inertia tensor and shifts the position of the pole of the Earth’s rotation. The spectrum of the ENSO has components with periods of about 6, 3.6, 2.8, and 2.4 years. These periods are all the multiples of the Chandler period T = 1.2 yr. and the principal period of nutation 18.6 yr. A nonlinear model for the Chandler polar motion has been constructed based on this empirical fact. In this model, the ENSO excites the Chandler polar motion by acting on the Earth at the frequencies of combinative resonance. At the same time, the Chandler polar motion induces a polar tide in the atmosphere and the World Ocean, which orders the ENSO. As a result, the dominant components in the noise spectrum of the ENSO are those with the periods indicated above.

scholarly journals On Investigations of the Tidal Waves Mf and Mm

1979 ◽  
Vol 82 ◽  
pp. 315-316
Author(s):  
G. P. Pil'nik
Keyword(s):  
Solid Earth ◽  
Elastic Properties ◽  
Earth Tides ◽  
Love Number ◽  
Astronomical Observations ◽  
Tidal Waves ◽  
The Earth ◽  
Astronomical Time ◽  
Solid Earth Tides

The comparison of astronomical time observations with the theory of solid-Earth tides makes it possible to determine the Love number, k, which characterizes the elastic properties of the Earth. In addition, the comparison of values of k determined from different tidal waves allows us to judge the accuracy of the nutational theory in astronomical observations since both tides and the Earth's nutation are produced by the same causes.

scholarly journals On the Relation between the Rotation of the Earth and Solar Activity

1972 ◽  
Vol 48 ◽  
pp. 231-233
Author(s):  
Chikara Sugawa ◽  
Chuichi Kakuta ◽  
Hideo Matsukura
Keyword(s):  
Solar Activity ◽  
Solid Earth ◽  
Polar Motion ◽  
Rotational Velocity ◽  
Lower Atmosphere ◽  
Neutral Atmosphere ◽  
Symmetric Mode ◽  
Axially Symmetric ◽  
The Earth ◽  
Long Time

Solar activity may affect the rotation of the solid Earth by coupling between the lower neutral atmosphere and the solid Earth. It attacks directly the lower atmosphere in the non-axially symmetric mode and may trigger off variation of the amplitude of the annual terms in the polar motion. The indirect effect of solar activity may be associated with some proper oscillation of the atmospheric coupling with the ocean in the axially symmetric mode of the atmospheric motion. The shift of airmass along the rotating axis of the Earth corresponds well with the changes of the Earth's rotational velocity and the Chandler amplitude in the polar motion for long time variation.

The status of Chandler wobble

2020 ◽  
Author(s):  
Guocheng Wang ◽  
Lintao Liu ◽  
Jinzhao Liu ◽  
Yi Tu
Keyword(s):  
Edge Effect ◽  
Polar Motion ◽  
Chandler Wobble ◽  
Basis Pursuit ◽  
Fourier Basis ◽  
The Earth ◽  
The Status ◽  
Band Pass ◽  
Main Components ◽  
Annual Wobble

<p>The Chandler wobble (CW) and Annual wobble (AW) are the main components of the Earth’s Polar motion, which play an important role in our understanding of their excitations. The Fourier Basis Pursuit Band-Pass Filtering (FBPBPF) method, which can effectively suppress the edge effect, are applied to extract the CW and AW in Earth's polar motion during 1900-2016. Through analyze the variation of CW extracted by the FBPBPF method, we find that the amplitude of the CW has been diminishing since 1995. However, the amplitude of the CW had stopped decline in the last year, and start to increase at now.</p>

scholarly journals An Elasto-viscous Model of the Earth

1988 ◽  
Vol 129 ◽  
pp. 411-412
Author(s):  
S. Losito ◽  
B. Pernice ◽  
D. Picca ◽  
G. Verrone
Keyword(s):  
Polar Motion ◽  
Free Oscillation ◽  
Liquid Core ◽  
Equation Of Motion ◽  
Chandler Wobble ◽  
Viscous Coupling ◽  
The Earth ◽  
Similar Term ◽  
Annual Term ◽  
One Year

A two-symmetric-rigid-rotators model of the Earth has been studied, under the hypothesis of elasto-viscous coupling. The free Eulerian equation of motion has been solved in the linear approximation related to small wobbling amplitudes. Under these hypotheses, polar motion is stable, and the angular velocity of the Earth is the sum of three vectors rotating with different frequencies and damped amplitudes. One of these terms turns out to be retrograde with a quasidiurnal frequency and could be identified with a similar term appearing in liquid core models of the Earth. The other two terms are identified with the Chandler wobble and the annual term according to observational data. The elastic coupling produces, in the time variation of L.O.D., a periodic term whose frequency is about one year. It could be hypothesized that the “decade fluctuation” could be partially attributed to the free oscillation of the Earth.

scholarly journals The Theory of the Earth's Orientation, with Some New Results for Nutation

1988 ◽  
Vol 129 ◽  
pp. 381-390
Author(s):  
John M. Wahr
Keyword(s):  
Time Scales ◽  
Rotation Rate ◽  
Polar Motion ◽  
Rotation Axis ◽  
Dynamical Behavior ◽  
Inertial Space ◽  
The Earth ◽  
Deep Interior ◽  
Geographical Position ◽  
Rotation Of The Earth

The rotation of the earth is variable at a number of time scales, from a few days to thousands of years and longer. Variations occur in the rotation rate, in the geographical position of the rotation axis (referred to as polar motion), and in the position of the axis relative to inertial space (referred to as nutation and precession). The interpretations of the various observations have implications for the dynamical behavior and structure of the earth's deep interior, and for various aspects of meteorology and oceanography. These are reviewed below. Also included is an Appendix describing a model of the diurnal resonance in nutation for a non-hydrostatically pre-stressed earth.

scholarly journals The Period of the Chandler Wobble

1980 ◽  
Vol 78 ◽  
pp. 187-193
Author(s):  
F. A. Dahlen
Keyword(s):  
Angular Momentum ◽  
Inner Core ◽  
Center Of Mass ◽  
Angular Frequency ◽  
Chandler Wobble ◽  
Earth Model ◽  
The Earth ◽  
Fluid Core ◽  
Relative Angular Momentum ◽  
The Mean

Realistic models of the Earth are known to possess a solid anelastic inner core, mantle and crust, and a fluid core and oceans. How might we go about calculating the theoretical free period of the Chandler wobble of such an Earth model? Let xi be a set of Cartesian axes with an origin at the center of mass, and let ωi be the instantaneous angular velocity of rotation of these axes with respect to inertial space. The net angular momentum is then Cijωj + hi, where Cij is the inertia tensor, and hi is the relative angular momentum. Let us affix the axes xi in the mantle and crust by stipulating that the relative angular momentum is that of the core and oceans alone, i.e., hi (mantle and crust) = 0; hi = hi (core and oceans). For an infinitesimal free oscillation of angular frequency σ, we can write ωi = Ω(δi3 + mi eiσt), Cij = A(δilδjl + δi2δj2) + Cδi3δj3 + cij eiσt, and hi = hi eiσt, where Ω is the mean rate of rotation and A and C are the mean equatorial and polar moments of inertia.

Reference Coordinate System Requirements for Geophysics

1975 ◽  
Vol 26 ◽  
pp. 87-92
Author(s):  
P. L. Bender
Keyword(s):  
Coordinate System ◽  
Polar Motion ◽  
Main Part ◽  
Measurement Techniques ◽  
Reference Points ◽  
Angular Motion ◽  
Coordinate Systems ◽  
Axis Of Rotation ◽  
The Earth ◽  
Fixed System

AbstractFive important geodynamical quantities which are closely linked are: 1) motions of points on the Earth’s surface; 2)polar motion; 3) changes in UT1-UTC; 4) nutation; and 5) motion of the geocenter. For each of these we expect to achieve measurements in the near future which have an accuracy of 1 to 3 cm or 0.3 to 1 milliarcsec.From a metrological point of view, one can say simply: “Measure each quantity against whichever coordinate system you can make the most accurate measurements with respect to”. I believe that this statement should serve as a guiding principle for the recommendations of the colloquium. However, it also is important that the coordinate systems help to provide a clear separation between the different phenomena of interest, and correspond closely to the conceptual definitions in terms of which geophysicists think about the phenomena.In any discussion of angular motion in space, both a “body-fixed” system and a “space-fixed” system are used. Some relevant types of coordinate systems, reference directions, or reference points which have been considered are: 1) celestial systems based on optical star catalogs, distant galaxies, radio source catalogs, or the Moon and inner planets; 2) the Earth’s axis of rotation, which defines a line through the Earth as well as a celestial reference direction; 3) the geocenter; and 4) “quasi-Earth-fixed” coordinate systems.When a geophysicists discusses UT1 and polar motion, he usually is thinking of the angular motion of the main part of the mantle with respect to an inertial frame and to the direction of the spin axis. Since the velocities of relative motion in most of the mantle are expectd to be extremely small, even if “substantial” deep convection is occurring, the conceptual “quasi-Earth-fixed” reference frame seems well defined. Methods for realizing a close approximation to this frame fortunately exist. Hopefully, this colloquium will recommend procedures for establishing and maintaining such a system for use in geodynamics. Motion of points on the Earth’s surface and of the geocenter can be measured against such a system with the full accuracy of the new techniques.The situation with respect to celestial reference frames is different. The various measurement techniques give changes in the orientation of the Earth, relative to different systems, so that we would like to know the relative motions of the systems in order to compare the results. However, there does not appear to be a need for defining any new system. Subjective figures of merit for the various system dependon both the accuracy with which measurements can be made against them and the degree to which they can be related to inertial systems.The main coordinate system requirement related to the 5 geodynamic quantities discussed in this talk is thus for the establishment and maintenance of a “quasi-Earth-fixed” coordinate system which closely approximates the motion of the main part of the mantle. Changes in the orientation of this system with respect to the various celestial systems can be determined by both the new and the conventional techniques, provided that some knowledge of changes in the local vertical is available. Changes in the axis of rotation and in the geocenter with respect to this system also can be obtained, as well as measurements of nutation.

Ups and Downs

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Mantle Convection ◽  
Laboratory Experiments ◽  
Inner Core ◽  
Computer Modelling ◽  
Great Depth ◽  
New Horizons ◽  
The Core ◽  
The Earth ◽  
The World ◽  
The 1960S

Despite the dumbing-down of education in recent years, it would be unusual to find a ten-year-old who could not name the major continents on a map of the world. Yet how many adults have the faintest idea of the structures that exist within the Earth? Understandably, knowledge is limited by the fact that the Earth’s interior is less accessible than the surface of Pluto, mapped in 2016 by the NASA New Horizons spacecraft. Indeed, Pluto, 7.5 billion kilometres from Earth, was discovered six years earlier than the similar-sized inner core of our planet. Fortunately, modern seismic techniques enable us to image the mantle right down to the core, while laboratory experiments simulating the pressures and temperatures at great depth, combined with computer modelling of mantle convection, help identify its mineral and chemical composition. The results are providing the most rapid advances in our understanding of how this planet works since the great revolution of the 1960s.

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