Quasi-periodic wind signal as a possible excitation of Chandler wobble

The atmospheric contribution to the excitation of the Chandler wobble (CW) is studied for a period of about 11 years period beginning in September 1983, using the wobble data set (SPACE93). Two atmospheric angular momentum (AAM) functions are employed; one is based on Japan Meteorological Agency (JMA) data, and the other is based on U.S. National Meteorological Center (NMC) data. In the vicinity of the Chandler frequency, the excitation power for both AAM functions is comparable with that inferred from the observed wobble. If we separate the AAM excitation into wind and pressure effects, the wind contribution exceeds the pressure contribution around the Chandler frequency. In addition, the JMA wind AAM function reveals a spectral peak around the Chandler frequency. Significant coherence with the inferred excitation exceeding the 99% confidence level can be recognized for both JMA and NMC wind excitation. We propose that the wind contribution to the excitation of polar motion may be somewhat larger than at other frequencies because of the existence of quasi-periodic atmospheric variations that have been found in other investigations. In a narrow-band analysis of the excitation using least squares fit sinusoids, we found that both the amplitude and phase of the inferred excitation near the Chandler band indicate their strong dependence on the assumed Chandler period and that an assumed CW period of 431 days caused atmospheric and observed excitations to agree most closely.