2. Possible excitation of the Chandler wobble by the annual oscillation of polar motion Kosek Wiesław Space Research Centre, Polish Academy of Sciences Annual Seminar of Commission of Satellite Geodesy, Committee Space Research PAS Section of Geodetic Networks, Committee of Geodesy PAS, Section of Geodynamics, Committee of Geodesy PAS, Space Research Centre PAS. EARTH ROTATION AND SATELLITE GEODESY - FROM ASTROMETRY TO GNSS Warsaw, 18-19 September 2003

3. Chandler wobble excitation The atmospheric wind and IB pressure variations maintain a major part of the observed Chandler Wobble. However the wind signal dominates over the IB pressure term in the vicinity of the Chandler frequency (Furuya et al. 1996; Aoyama and Naito 2001). Celaya et al. (1999) using the results of a coupled atmosphere-ocean- land climate model, concluded that some combination of atmospheric and oceanic processes probably have enough power to excite the Chandler wobble. Using an 11-year time series of the OAM Brzeziński and Nastula (2002) concluded that, within the limits of accuracy, the coupled system atmosphere/ocean fully explains the observed Chandler wobble during the period 1985-1996. The most important mechanism exciting the Chandler wobble in 1985-1996 was ocean-bottom pressure fluctuations, which contribute about twice as much excitation power as do atmospheric pressure fluctuations (Gross 2002).

4. Data EOPC01 (1846.0 - 2000.0), Δt =0.05 yr http://hpiers.obspm.fr/eop-pc/ EOPC04 (1962.0 - 2003.6), Δ t = 1 day http://hpiers.obspm.fr/eop-pc/ USNO (1976.0 - 2003.6), Δ t = 1 day (finals.all ) http://maia.usno.navy.mil/bulletin-a.html

5. The mean determination error of x, y pole coordinates data

6. The FTBPF amplitude spectra of complex-valued pole coordinate data in 1900-2003

7. The most energetic oscillations of polar motion computed by the FTBPF Chandler Annual

8. The amplitudes and phases of the Chandler and annual oscillations computed by the LS in 3 year time intervals, the Niño indices

9. The amplitude of the Chandler oscillation computed from the x, y data by the FTBPF and from the x – i y data by the LS method in 5 year time intervals

10. Transformation of x, y pole coordinates data to polar coordinate system radius angular velocity length of polar motion path mean pole

11. The mean pole computed by the Ormsby LPF - filter length,- number of data, - cutoff frequency, - cutoff period, - roll-off termination frequency. - pole coordinates data, 1849 2003

12. Corr. Coeff. 1900-2003 0.864 1950-2003 0.899

13. The FTBPF time-frequency amplitude spectra of polar motion radius and angular velocity

14. The time-frequency coherence between the radius and angular velocity computed using the Morlet Wavelet Transform

15. The length of polar motion path and the envelope of the Chandler oscillation

16. LS Phases computed in 5 year time intervals of the Chandler and annual oscillations, periods estimated from them and the beat period

17. Niño The beat period of the Chandler and annual oscillation computed from their LS phases in 5 and 6 year time intervals. First derivative of the Chandler amplitude computed by the LS in 5 year time intervals and by the FTBPF. The Niño indices.

18. The amplitudes and phases of 6-7yr oscillation in the radius computed in 12, 13 year time intervals by the LS method. The periods computed from the phases

19. The periods of the 6-7 yr oscillation in the radius computed from the LS phases in 12, 13 year time intervals. Beat period of the Chandler and annual oscillations computed from the LS phases in 5 and 6 year time intervals. First derivative of the Chandler amplitudes computed by the LS in 4, 5 and 6 year time intervals. 0.654 Corr. Coeff. 1984-2000 Corr. Coeff. 1984-1997 0.510

20. Conclusions Amplitudes and phases of the Chandler oscillation are smoother than those of the annual oscillation. The phase of the annual oscillation had maximum values and the beat period of the Chandler and annual oscillation had minimum values before the biggest 1982/83 and 1997/98 El Niño events. Long period variations with periods greater than 6 years in the length of polar motion path are due to variable amplitude of the Chandler oscillation. The increase of the Chandler oscillation amplitude is associated with the increase of the beat period of the Chandler and annual oscillations. It means that the annual oscillation period gets closer to the Chandler one. Thus, the Chandler amplitude increases during increase of the period (decrease of the phase) of the annual oscillation. The Chandler oscillation can be excited by variable annual oscillation.