The First-time Absence of the Chandler Wobble since 2015 and its Implications for Excitation Processes

Abstract The Chandler Wobble period is considered a single time-invariable constant, ~ 1.2 years. To confirm the time-invariability of the Chandler period, we preliminarily estimated the Chandler period using 50 years’ long space geodetic data under the minimum excitation assumption. Unexpectedly, the estimated period has been shortened by more than 60 days since about 2005, which we consider unreal but significant. Moreover, by simple least-squares modeling, we found the Chandler Wobble started to be weaker in 2005 and almost disappeared in 2015. We interpret these results in both excitation and wobble domains as caused by the absence of the Chandler Wobble for the first time in the observation history. Assuming no excitations of the Chandler Wobble since 2005, the rather abrupt damping suggests that the Q-value is below 25, and that the excitation power of the Chandler Wobble should be greater than previously thought. Meanwhile, although the atmosphere and ocean are currently believed to be the excitation sources of the Chandler wobble, the available atmospheric and oceanic angular momentum functions do not show any temporal changes in terms of the excitation power around the Chandler frequency even after 2005, and cannot explain the recent anomaly of the Chandler Wobble.