The Earth’s variable Chandler wobble

Abstract

Aims. We investigated the causes of the Earth's Chandler wobble variability over the past 60 years. Our approach is based on integrating of the atmospheric and oceanic angular momentum computed by global circulation models. We directly compared the result of the integration with the Earth's pole coordinate observed by precise astrometric, space, and geodetic techniques. This approach differs from the traditional approach in which the observed polar motion is transformed into a so-called geodetic excitation function, and compared afterwards with the angular momentum of the external geophysical fluid layers. Methods. In the time domain, we integrated the atmospheric angular momentum time series from the National Center for Environmental Prediction/National Center for Atmospheric Research Reanalysis project and the oceanic angular momentum data from the ECCO consortium. We extracted the Chandler wobble from this modeled polar motion by singular spectrum analysis, and compared it with the Chandler wobble extracted from the observed polar motion given by the International Earth Rotation and Reference Systems Service data. Results. We showed that the combination of the atmosphere and the oceans explains most of the observed Chandler wobble variations, and is consistent with results reported in the literature and obtained with the traditional approach. Our approach allows one to appreciate the separate contributions of the atmosphere and the oceans to the various bumps and valleys observed in the Chandler wobble. Though the atmosphere explains the Chandler wobble amplitude variations between 1949 and 1970, the reexcitation of the Chandler wobble that begins in the 1980s, after a minimum around 1970, and that reaches its maximum in the late 1990s is due to the oceans, while the atmospheric contribution remains stable within the same period.

Geophysics From Terrestrial Time‐Variable Gravity Measurements

“…As their periods are close together, their addition generates a 6–7 year beat period. The annual wobble is a forced motion only, mainly by the atmosphere, while the Chandler wobble is a resonant oscillation forced by the atmosphere and the oceans (Bizouard et al, ; Plag, ). The Chandler wobble can be considered as a continuously or, at least, frequently excited, damped harmonic oscillation.…”

Chandler wobble parameters from SLR and GRACE

“…In the past, when the physical processes exciting the Chandler wobble were not fully known, the period and Q were determined by applying a statistical model of the excitation process [e.g., Jeffreys , ; Wilson and Haubrich , ; Wilson and Vicente , , ]. While the exact mechanism of Chandler wobble excitation is still under investigation, it has been shown that processes in the oceans and atmosphere are energetic enough to excite the Chandler wobble [ Gross , ; Brzeziński and Nastula , ; Brzeziński et al , ; Gross et al , , ; Liao et al , ; Bizouard et al , ; Nastula et al , ; Zotov and Bizouard , ; Gross , ]. The role of continental hydrology in polar motion excitation is not as well known as those of the atmosphere and oceans [ Dobslaw et al , , Brzeziński et al , , ; Nastula et al , , ; Seoane et al , ].…”

On the Eigen‐Mode Excitation of Linear Oscillators and the Earth's Polar Motion

“…A prominent eigen‐mode of a gigantic linear oscillator that persists in spite of the three shortages is the Chandler Wobble: a supposedly free circular eigen‐wobble by the Earth's rotational axis around the axis of spheroidal symmetry at a period of ≈433 days (e.g., refs. [1–6]). Related but a little more complicated than a 1D oscillator is the phenomenon of the Earth's background noise known as the hum, that is, irregular but persistent oscillations detected by superconducting gravimeters in a very quiet environment.…”