The upper curve in the second graph shows the PDO reconstruction of D’Arrigo et al. (2001) between 1707 and 1972. The reconstruction has been smoothed with a 15-year running mean filter to eliminate short-term fluctuations. Superimposed on this PDO reconstruction is the instrumental mean annual PDO index (Mantua 2007) which extends the PDO series up to the year 2000. The lower curve in the second graph shows the absolute deviation of the Earth’s LOD from its long-term trend between 1656 to 2005. The data in this figure has also been smoothed with a 15-year running mean filter.
A comparison between the upper and lower curves in the second graph shows that there is a remarkable agreement between the years of the peak (absolute) deviations of the LOD from the long-term trend and the years where the phase of the PDO reconstruction is most positive. While the correlation is not perfect, it is convincing enough to conclude the PDO index is another good example of a climate system that is directly associated with changes in the Earth's rotation rate.
What is even more remarkable is the fact that LOD variations preceed those seen in the PDO by an average of eight years. So whatever causes the deviations in the LOD from its long-term trend must also be responsible for flipping the phase of the PDO.
The solid curve in the first graph (above) shows the absolute deviation of the Earth’s LOD from its long-term trend between 1656 to 2005. The data in this figure has also been smoothed with a 15-year running mean filter. Superimposed on this plot is a scaled version of the assymmtery in the Sun's motion about the centre-of-mass of the Solar System. The reader can see for themselves that, from 1700 to 2000 A.D., on every occasion where the Sun has experienced a maximum in the asymmetry of its motion about the CM of the Solar System, the Earth has also experienced a significant deviation in its LOD from that expected from the long-term trends.
The question is: "How does the pattern in sea surface temperatures in the Northern Pacific ocean (i.e. the PDO) know about the postion of the Sun with respect to the barycentre of the Solar System?"