Using Constraints from Satellite Gravimetry to Study Meteorological Excitations of the Chandler Wobble for an Earth Model with Frequency-dependent Responses

Abstract:

What maintain(s) the damping Chandler wobble (CW) is still under debate though meteorological excitations are now more preferred. However, controversial results have been obtained: Gross [2000] and Gross et al. [2003] suggested oceanic processes are more efficient to excite the CW than atmospheric ones during 1980 – 2000. Brzezinski and Nastula [2002] concluded that their contributions are almost the same, and they can only provide ~80% of the power needed to maintain the CW observed during 1985 – 1996.

Polar motion excitations involve not only the perturbations within the Earth system (namely, mass redistributions and motions of relative to the mantle), but also the Earth’s responses to those perturbations (namely, the rheology of the Earth). Chen et al. [2013a] developed an improved theory for polar motion excitation taking into account the Earth’s frequency-dependent responses, of which the polar motion transfer functions are ~10% higher than those of previous theories around the CW band. Chen et al. [2013b] compared the geophysical excitations derived from various global atmospheric, oceanic and hydrological models (NCEP, ECCO, ERA40, ERAinterim and ECMWF operational products), and found significant and broad-band discrepancies for models released by different institutes. In addition, the atmosphere, ocean and hydrology models are usually developed in a somewhat independent manner and thus the global (atmospheric, oceanic and hydrological) mass is not conserved [e.g., Yan and Chao, 2012]. Therefore, the matter-term excitations estimated from those models are problematic. In one word, it is unlikely to obtain reliable conclusions on meteorological excitations of CW on the basis of the original meteorological models.

Satellite gravimetry can measure mass transportations caused by atmospheric, oceanic and hydrological processes much more accurately than those provided by the original meteorological models, and can force the global (atmospheric, oceanic and hydrological) mass to be conserved. Therefore, it might be promising to obtain better understanding on meteorological excitations of CW by assimilating the time-variable gravity data from GRACE and SLR to improve the matter terms of the meteorological excitations, and adopting the new polar motion theory of Chen et al. [2013a].