On Two Formulations of Polar Motion and Identification of Its Sources
Differences in formulation of the equations of celestial mechanics may result in differences in interpretation. This paper focuses on the Liouville-Euler system of differential equations as first discussed by Laplace. In the “modern” textbook presentation of the equations, variations in polar motion...
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MDPI AG
2022-10-01
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| Online Access: | https://www.mdpi.com/2076-3263/12/11/398 |
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| author | Fernando Lopes Vincent Courtillot Dominique Gibert Jean-Louis Le Mouël |
| author_facet | Fernando Lopes Vincent Courtillot Dominique Gibert Jean-Louis Le Mouël |
| author_sort | Fernando Lopes |
| collection | DOAJ |
| description | Differences in formulation of the equations of celestial mechanics may result in differences in interpretation. This paper focuses on the Liouville-Euler system of differential equations as first discussed by Laplace. In the “modern” textbook presentation of the equations, variations in polar motion and in length of day are decoupled. Their source terms are assumed to result from redistribution of masses and torques linked to Earth elasticity, large earthquakes, or external forcing by the fluid envelopes. In the “classical” presentation, polar motion is governed by the inclination of Earth’s rotation pole and the derivative of its declination (close to length of day, lod). The duration and modulation of oscillatory components such as the Chandler wobble is accounted for by variations in polar inclination. The “classical” approach also implies that there should be a strong link between the rotations and the torques exerted by the planets of the solar system. Indeed there is, such as the remarkable agreement between the sum of forces exerted by the four Jovian planets and components of Earth’s polar motion. Singular Spectral Analysis of lod (using more than 50 years of data) finds nine components, all with physical sense: first comes a “trend”, then oscillations with periods of ∼80 yrs (Gleissberg cycle), 18.6 yrs, 11 yrs (Schwabe), 1 year and 0.5 yr (Earth revolution and first harmonic), 27.54 days, 13.66 days, 13.63 days and 9.13 days (Moon synodic period and harmonics). Components with luni-solar periods account for 95% of the total variance of the lod. We believe there is value in following Laplace’s approach: it leads to the suggestion that all the oscillatory components with extraterrestrial periods (whose origin could be found in the planetary and solar torques), should be present in the series of sunspots and indeed, they are. |
| first_indexed | 2024-03-09T19:03:48Z |
| format | Article |
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| issn | 2076-3263 |
| language | English |
| last_indexed | 2024-03-09T19:03:48Z |
| publishDate | 2022-10-01 |
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| record_format | Article |
| series | Geosciences |
| spelling | doaj.art-b1d3ed2f5cde47c2a0c8d27ced44a4f22023-11-24T04:49:46ZengMDPI AGGeosciences2076-32632022-10-01121139810.3390/geosciences12110398On Two Formulations of Polar Motion and Identification of Its SourcesFernando Lopes0Vincent Courtillot1Dominique Gibert2Jean-Louis Le Mouël3Institut de Physique du Globe de Paris, Université de Paris, 75005 Paris, FranceInstitut de Physique du Globe de Paris, Université de Paris, 75005 Paris, FranceLGL-TPE, Université de Lyon 1, ENSL, CNRS, UMR 5276, 69622 Villeurbanne, FranceInstitut de Physique du Globe de Paris, Université de Paris, 75005 Paris, FranceDifferences in formulation of the equations of celestial mechanics may result in differences in interpretation. This paper focuses on the Liouville-Euler system of differential equations as first discussed by Laplace. In the “modern” textbook presentation of the equations, variations in polar motion and in length of day are decoupled. Their source terms are assumed to result from redistribution of masses and torques linked to Earth elasticity, large earthquakes, or external forcing by the fluid envelopes. In the “classical” presentation, polar motion is governed by the inclination of Earth’s rotation pole and the derivative of its declination (close to length of day, lod). The duration and modulation of oscillatory components such as the Chandler wobble is accounted for by variations in polar inclination. The “classical” approach also implies that there should be a strong link between the rotations and the torques exerted by the planets of the solar system. Indeed there is, such as the remarkable agreement between the sum of forces exerted by the four Jovian planets and components of Earth’s polar motion. Singular Spectral Analysis of lod (using more than 50 years of data) finds nine components, all with physical sense: first comes a “trend”, then oscillations with periods of ∼80 yrs (Gleissberg cycle), 18.6 yrs, 11 yrs (Schwabe), 1 year and 0.5 yr (Earth revolution and first harmonic), 27.54 days, 13.66 days, 13.63 days and 9.13 days (Moon synodic period and harmonics). Components with luni-solar periods account for 95% of the total variance of the lod. We believe there is value in following Laplace’s approach: it leads to the suggestion that all the oscillatory components with extraterrestrial periods (whose origin could be found in the planetary and solar torques), should be present in the series of sunspots and indeed, they are.https://www.mdpi.com/2076-3263/12/11/398pole motionlength-of-dayLiouville-Euler |
| spellingShingle | Fernando Lopes Vincent Courtillot Dominique Gibert Jean-Louis Le Mouël On Two Formulations of Polar Motion and Identification of Its Sources Geosciences pole motion length-of-day Liouville-Euler |
| title | On Two Formulations of Polar Motion and Identification of Its Sources |
| title_full | On Two Formulations of Polar Motion and Identification of Its Sources |
| title_fullStr | On Two Formulations of Polar Motion and Identification of Its Sources |
| title_full_unstemmed | On Two Formulations of Polar Motion and Identification of Its Sources |
| title_short | On Two Formulations of Polar Motion and Identification of Its Sources |
| title_sort | on two formulations of polar motion and identification of its sources |
| topic | pole motion length-of-day Liouville-Euler |
| url | https://www.mdpi.com/2076-3263/12/11/398 |
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