The Recent Absence of the Chandler wobble and Its Implications for Climate

Yamaguchi and Furuya (2022) demonstrated that the Chandler wobble (CW) is missing after 2015. Based on the analyses from the optimization of the Chandler period in the excitation domain and from the modeling of the absence of the 6-years' beat in polar motion data, we suggested the anomaly started from around 2005. Because the annual wobble (AW) does not change its phase by definition and its amplitude variation is insignificant, we can trace the CW amplitude back to the 1900s by removing the AW derived by fitting the post-2015 polar motion data. It turned out that the CW amplitude after 2015 was much smaller than the CW amplitude in the 1920s known as the former "minimum" (and nearly zero) . As of writing this abstract, it seems that CW is not re-excited yet.

Given the un-excitation of the CW since ~2005, the e-folding damping time turns out to be less than 10 years, from which we can readily infer that the Q for CW is below 26. This is the smallest estimate of the Q for CW, to our knowledge, and has also important implications for the excitation mechanisms and climate dynamics as well. Although it is widely accepted that atmospheric and oceanic angular momentum (AAM and OAM) changes are responsible for the excitation of CW (e.g., Gross 2000), it is still an open question if the CW excitations by AAM/OAM changes are random or resonant. Whereas numerous previous studies have explicitly or implicitly assumed a random noise excitation, we can recall several earlier studies that conform to the resonant excitation process.

The absence of CW for several years indicates that the spectral power of the excitation around the Chandler frequency has become much smaller than previously. While the random excitation model will regard the smallest power level caused by coincidence (Chao and Chung, 2012), the resonant excitation model will correspond to an abrupt termination of continual excitation processes within a narrow band around the Chandler frequency. Such a coherent atmospheric signals have been suggested before (Furuya et al, 1996, 1997; Plag, 1997; Aoyama et al. 2003). Also, the small-Q is more consistent with the resonant excitation process.

We need to demonstrate what has been happening in the atmosphere in the recent decade. It deserves to re-examine the effect of atmospheric wind term, using the state-of-the-art analysis data.