Climate‐driven polar motion

Abstract

Abstract. The output of a coupled climate system model provides a synthetic climate record with temporal and spatial coverage not attainable with observational data, allowing evaluation of climatic excitation of polar motion on timescales of months to decades. Analysis of the geodetically inferred Chandler excitation power shows that it has fluctuated by up to 90% since 1900 and that it has characteristics representative of a stationary Gaussian process. Our model-predicted climate excitation of the Chandler wobble also exhibits variable power comparable to the observed. Ocean currents and bottom pressure shifts acting together can alone drive the 14-month wobble. The same is true of the excitation generated by the combined effects of barometric pressure and winds. The oceanic and atmospheric contributions are this large because of a relatively high degree of constructive interference between seafloor pressure and currents and between atmospheric pressure and winds. In contrast, excitation by the redistribution of water on land appears largely insignificant. Not surprisingly, the full climate effect is even more capable of driving the wobble than the effects of the oceans or atmosphere alone are. Our match to the observed annual excitation is also improved, by about 17%, over previous estimates made with historical climate data. Efforts to explain the 30-year Markowitz wobble meet with less success. Even so, at periods ranging from months to decades, excitation generated by a model of a coupled climate system makes a close approximation to the amphtude of what is geodetically observed.

The Earth’s variable Chandler wobble

“…Doing so, we assumed that the atmosphere and the oceans are the only sources of the observed CW, thus neglecting the contribution of continental waters. However, based on a predictive model, Celaya et al (1999) concluded that the hydrological forcing of the CW does not compete with atmosphere and oceans.…”

“…He associated the temporal characteristics of the fourteen to sixteen months oscillation over the northern hemisphere with frequency or phase shifts of the CW. According to Celaya et al (1999), Gross (2000), and Brzeziński & Nastula (2002), the CW excitation is accounted for, on average, by the atmosphere and oceans. Following Aoyama et al (2003), atmospheric and ocean-bottom pressure and winds are comparable sources of excitation, intermittently playing a prominent role.…”

Atmospheric quasi-14 month fluctuation and excitation of the Chandler wobble

“…It should be noticed that the latest atmospheric general circulation models (AGCM), in general, reasonably simulate the axial angular momentum variations (e.g., Hide et al, 1997) but not the equatorial ones in comparison with the angular momentum variations inferred from the observed rotation of the Earth. In addition, the simulation study based on AGCM demonstrated that the atmospheric excitation to CW shows strong time variability (Celaya et al, 1999).…”

“…Despite the fact that its excitation processes inside and outside the Earth's mantle have been proposed, no major source has yet been identified. Lately, however, variations in the atmosphere and ocean have been widely noticed as a possible source (Wahr, 1983;Furuya et al, 1996;Plag, 1997;Celaya et al, 1999;Ponte and Stammer, 1999;Gross, 2000;Aoyama and Naito, 2001;Gross et al, 2003).…”

Atmospheric, hydrological, and ocean current contributions to Earth's annual wobble and length‐of‐day signals based on output from a climate model

“…For example, using a climate model, Celaya et al [1999] found that the atmospheric, oceanic, and hydrological excitations on the annual wobble were improved by $17% over some previous estimates made with historical data. Celaya et al also discussed the excitation of the Chandler wobble.…”