Abstract We apply complex Morlet wavelet transform to three polar motion data series, and derive quasi-instantaneous periods of the Chandler and annual wobble by differencing the wavelet transform results versus the scale factor, and then find their zero points. The results show that the mean periods of the Chandler (annual) wobble are 430.71±1.07 (365.24±0.11) and 432.71±0.42 (365.23±0.18) mean solar days for the data sets of 1900--2001 and 1940--2001, respectively. The maximum relative variation of the quasi-instantaneous period to the mean of the Chandler wobble is less than 1.5 % during 1900--2001 (3%--5% during 1920--1940), and that of the annual wobble is less than 1.6 % during 1900--2001. Quasi-instantaneous and mean values of Q are also derived by using the energy density---period profile of the Chandler wobble. An asymptotic value of Q=36.7 is obtained by fitting polynomial of exponential of σ ^{- 2} to the relationship between Q and σ during 1940--2001.

Keywords polar motion --- Chandler wobble --- wavelet transform --- instantaneous period

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