New determination of period and quality factor of Chandler wobble, considering geophysical excitations

Vondrák, J.; Ron, C.; Chapanov, Yavor

doi:10.1016/j.asr.2016.12.001

Cited by 14 publications

(13 citation statements)

References 29 publications

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“…This empirical term was added to the model to get rid of systematic residuals that the authors found when comparing their theoretical model with observations. We have followed a procedure similar to the one that we used to derive parameters of Chandler wobble (Vondrák et al 2017), but the situation here is more complicated because of the strong resonances that must be considered. Thus we propose a combination of direct and indirect approach.…”

Section: New Methods Of Determining T F Q Fmentioning

confidence: 99%

“…There is a simple relation between a frequency in terrestrial and celestial reference frames, σ = σ + Ω, where Ω = 6.30038 rad/day is the mean speed of rotation of the Earth. Here we use complex Chandler frequency σ C = 6.314935 + 0.000208i, based on Chandler wobble parameters derived recently by Vondrák et al (2017). The complex effective angular momentum functions χ = χ 1 +iχ 2 in terrestrial frame (their definition being given by Barnes et al 1983) can be transformed into celestial frame, using a simple formula χ = −χe iφ , where φ is the Greenwich sidereal time; retrograde quasidiurnal signal in terrestrial frame becomes long-periodic in celestial frame.…”

Section: New Methods Of Determining T F Q Fmentioning

confidence: 99%

“…Seven epochs of geomagnetic jerks are used: 1991.0, 1994.0, 1999.0, 2007.5 (given by Malkin 2013), 2003.5, 2004.7 (after Olsen & Mandea 2008Mandea et al 2010), and 2011.0 (Chulliat & Maus 2014). Similarly to our recent work on Chandler wobble parameters (Vondrák et al 2017), we use a procedure consisting of several steps. First, the initial pole position P(0) is found to yield the best fit to observations in the interval between the beginning (1986.0) and the first GMJ epoch.…”

Section: Geophysical Excitationsmentioning

confidence: 99%

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New method for determining free core nutation parameters, considering geophysical effects

Vondrák

Ron

2017

A&A

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Context. In addition to the torques exerted by the Moon, Sun, and planets, changes of precession-nutation are known to be caused also by geophysical excitations. Recently studies suggest that geomagnetic jerks (GMJ) might be associated with sudden changes of phase and amplitude of free core nutation. We showed that using atmospheric and oceanic excitations with those by GMJ improves substantially the agreement with observed celestial pole offsets. Aims. Traditionally, the period T f and quality factor Q f of the free core nutation (FCN) are derived from VLBI-based celestial pole offsets (CPO). Either direct analysis of the observed CPO, or indirect method using resonant effects of nutation terms with frequencies close to FCN, are used. The latter method is usually preferred, since it yields more accurate results. Our aim is to combine both approaches to better derive FCN parameters. Methods. We numerically integrated the part of CPO that is due to geophysical excitations for different combinations of T f , Q f , using Brzeziński's broadband Liouville equations (Brzeziński 1994, Manuscripta geodaetica, 19, 157), and compared the results with the observed values of CPO. The values yielding the best fit were then estimated. The observed CPO, however, must be corrected for the change of nutation that is caused by the T f , Q f values different from those used to calculate IAU 2000 model of nutation. To this end, we have used the Mathews-Herring-Buffet transfer function and applied it to the five most affected terms of nutation (with periods 365.26, 182.62, 121.75, 27.55 and 13.66 days). Results. The results, based on the CPO data in the interval 1986.0-2016.0 and excitations with three different models, are presented. We demonstrate that better results are obtained if the influence of additional excitations at GMJ epochs is added to excitations by the atmosphere and oceans. Our preferred values are T f = 430.28 ± 0.04 mean solar days and Q f = 19 500 ± 200.

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Section: New Methods Of Determining T F Q Fmentioning

confidence: 99%

Section: New Methods Of Determining T F Q Fmentioning

confidence: 99%

Section: Geophysical Excitationsmentioning

confidence: 99%

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New method for determining free core nutation parameters, considering geophysical effects

Vondrák

Ron

2017

A&A

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“…The agreement with observations is improved when GMJ are considered (Vondrák and Ron 2016). The method has been applied to derive new estimates of the periods and Q of the Chandler Wobble (CW) and FCN (Vondrák et al 2017(Vondrák et al , 2019. 5.…”

Section: The Numerical Integration Of Brzeziński's Broad-bandmentioning

confidence: 99%

Report of the IAU/IAG Joint Working Group on Theory of Earth Rotation and Validation

Ferrándiz

Gross

Escapa

et al. 2020

International Association of Geodesy Symposia

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This report focuses on some selected scientific outcomes of the activities developed by the IAU/IAG Joint Working Group on Theory of Earth rotation and validation along the term 2015-2019. It is based on its end-of-term report to the IAG Commission 3 published in the Travaux de l'IAG 2015-2019, which in its turn updates previous reports to the IAG and IAU, particularly the triennial report 2015-2018 to the IAU Commission A2, and the medium term report to the IAG Commission 3 (2015-2017). The content of the report has served as a basis for the IAG General Assembly to adopt Resolution 5 on Improvement of Earth rotation theories and models.

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“…The CW and FCN observations that meet our precision criterion are displayed in Table . We note that, since the periods of CW and FCN might vary with time due to temporal mass migration such as ice melting, atmospheric and oceanic excitations, the accuracies of the CW and FCN observations are supposedly not better than 0.5 d. Hence, in this study we did not use the results given by Vondrák et al () and Vondrák and Ron (), which suggest the accuracies of the CW and FCN periods being 0.04 d, neither the FCN observations of Vondrák and Ron (), Lambert and Dehant (), and Krásná et al (), which suggest the accuracies of the FCN period being, respectively, 0.07, 0.4, and 0.1 d.…”

Section: Observed and Predicted Rotational Normal Mode Valuesmentioning

confidence: 82%

Formulation of a Triaxial Three‐Layered Earth Rotation: Theory and Rotational Normal Mode Solutions

Guo

Shen

2020

JGR Solid Earth

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In this study, we formulated a triaxial three‐layered anelastic Earth rotation theory considering various core‐mantle couplings, including the pressure and gravitational couplings acting on the elastic inner core by the outer core and mantle, and the viscoelectromagnetic couplings between the outer core and mantle and between the outer and inner cores. With this formulation, using the eigenvalue method, we solved four rotational normal modes, including the Chandler Wobble (CW), Free Core Nutation (FCN), Free Inner Core Nutation (FICN), and the Inner Core Wobble (ICW). The triaxiality of the actual Earth has notable effects on rotational normal modes, that is, 0.005, 0.0, −0.071, and 1.174 d (mean solar days), respectively, for the CW, FCN, FICN, and ICW. In the case that the triaxiality is bigger, for instance, if the Earth's equatorial dynamical ellipticity were 5.22×10−4, which is 1 order of magnitude larger than the presently determined ellipticity ( 2.2×10−5), the CW and ICW periods will be lengthened by 3.579 and 94.912 d, and the FICN period will be decreased by 0.591 d. Based on our present knowledge, the numerical solutions of the four normal modes under the new rotation frame suggest that the periods of CW, FCN, FICN, and ICW are, respectively, 432.2, 429.9, 934.0, and 2,718.7 d. Our theory for Earth can be extended to other planets in our solar system.

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New determination of period and quality factor of Chandler wobble, considering geophysical excitations

Cited by 14 publications

References 29 publications

New method for determining free core nutation parameters, considering geophysical effects

New method for determining free core nutation parameters, considering geophysical effects

Report of the IAU/IAG Joint Working Group on Theory of Earth Rotation and Validation

Formulation of a Triaxial Three‐Layered Earth Rotation: Theory and Rotational Normal Mode Solutions

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