Back in 2009, Anthony Watts and Basil Copeland did a study of the HADcruT3 temperature series and found some periodicities in the rate of warming of Earth’s surface. They created a model which achieved a reasonably good match:
Shown in Figure 6, the sinusoidal fit results in periods of 20.68, 9.22, 15.07 and 54.56 years, in that order of significance. These periodicities fall within the ranges of the spectra obtained using MTM spectrum analysis, and yield a sinusoidal model with an R2 of 0.60.
I didn’t realise the significance of the periods they found at the time, but now we are a bit further down the road of understanding solar system dynamics, it is starting to make more sense.
A very significant, high amplitude, sharp peak is evident in the spectrographic analysis of many temperature and solar proxies at around 205 years. This is known as the De Vries cycle (The page has been deleted at Wikipedia), commonly given as 200 or 210 years. It doesn’t seem to relate in any simple way to planetary frequencies, and this has been a puzzle. However, there have been some attempts to find combinations which fit the period.
Looking at the frequencies Anthony and Basil found, I realised there may be some connections with the De Vries cycle which will help us understand the links between the variables.
One of the peaks near the solar cycle length we found when Bart made a MEM spectral analysis of sunspot numbers matches the half period of the Jupiter-Saturn conjunction cycle – 9.93 years.
9.93 years multiplied by Anthony and Basil’s 20.68 year frequency gives 205.35 years; close to De Vries cycle length.
205.35 years divided by their 9.22 year frequency gives 22.27 years – close to the solar-magnetic Hale cycle length.
205.35 years divided by their 15.07 year frequency gives 13.62 years – close to a quarter (54.48/4=13.64) of their 54.56 year frequency.
54.56 years is close to five times the average solar cycle length (5×10.94=54.72 years), over the period of the HADcruT record they used.
Roy Martin found a solar pattern repeating at 55.15 years over a longer term, giving an average cycle length of 11.03 years. This is very close to the Venus-Earth-Jupiter cycle of 11.07 years.
But there’s more.
Anthony and Basil found that the frequencies also relate to Lunar periods.
because the bidecadal signal is harmonic, and readily discernible in the time domain representation of Figure 2 and Figure 6, we believe that a better attribution is the beat cycle explanation proposed by Bell , i.e. a cycle representing the combined influence of the 22 year double sunspot cycle and the 18.6 year lunar nodal cycle.
As for the decadal signal of 9.22 years, this is too short to be likely attributable to the 11 year solar cycle, but is very close to half the 18.6 year lunar nodal cycle, and thus may well be attributable to the lunar nodal cycle.
It’s also worth noting that they found a harmonic period period at 4.74 years in the spectrum of the temperature dataset, offset twice this period with Their 9.22 year period and we are near a quarter of the Lunar nodal cycle.
So how else might the Moon fit into the Luni-Solar picture? One very obvious fact is that the V-E-J average solar cycle length of 11.07 Earth orbits multiplied by the Lunar nodal cycle of 18.61 Earth orbits gives 206.01 - De Vries again! This means there will be beat periods around 27.3 and 58.3 years according to Ray Tomes (private communication). 27.3 years is half of Anthony and Basil’s 54.56 year period.
Solar cycle 24 has been a damp squib compared to preceding solar cycle 23. We haven’t seen such low activity levels solar cycle 6 reached its peak in 1806 – 206 years ago. The De Vries cycle seems likely to be a solar system wide period linked to the frequencies of planetary motion interactions, affecting both the Sun and Earth-Moon system.