The First-time Absence of Chandler Wobble since 2015 in the Observation History
Abstract
Chandler Wobble (CW) is one component of the Earth's polar motion. CW is considered as a free motion excited by mass redistribution of the atmosphere and ocean and their motion relative to the solid Earth (Gross, 2015). The observed Chandler period (P) is 433.7 ± 1.8 days (e.g., Furuya and Chao, 1996), and has been regarded as a single and time-invariable constant.
To confirm the time-invariability of the Chandler period, we preliminarily estimated the Chandler period using 50 years' long space geodetic data on the minimum excitation assumption (e.g., Wilson and Vicente, 1990). Unexpectedly, the estimated Chandler period has been shortened by more than 60 days since about 2005 and reached around 380 days, which we consider unreal but significant. By fitting the polar motion with the "standard" model containing CW, annual wobble (AW), and long-term motion and the model excluded CW, we found that CW started to be weaker in 2005 and almost disappeared in 2015. The estimated amplitude of CW is about 20 mas, we interpret these results in both excitation and wobble domain as the absence of CW for the first time in the observation history. To seek the cause of CW absence, we analyze the available atmospheric and oceanic angular momentum (AAM/OAM) functions that are archived at the Paris Observatory. The AAM and OAM are based on the National Centers for Environmental Prediction (NCEP) reanalysis data and the output from the Estimating the Circulation and Climate of the Ocean (ECCO) model, respectively. As a result, the AAM and OAM do not change regarding the excitation power around the Chandler frequency even after 2005. In addition, we integrate the non-seasonal AAM and OAM to see if the CW absence is reproduced, assuming that P and Q as 435 days and 100, respectively. We examined three distinct 10 years' coverage, starting from 1965, 1985, and 2005. The amplitude of the calculated CW in the three periods is systematically smaller than the observed CW, and we found no anomaly after 2005. The result suggests that the theory of CW excitation and/or the available excitation functions (AAM and/or OAM) are not complete to explain.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.G15A..06Y