N.Atl S.Atl power spectrum

Power density from cross-correlation of tropical N. Atlantic and S. Atlantic SST.

6.002
9.163
10.21
and 18.6 notably marked by a zero.

The line of apsides and line of nodes come into mutual alignment on average twice every 5.997 years. This time interval, 1/(1/8.8475-1/18.6134) the perigean eclipse cycle, is also the beat period between the anomalistic and nodical months.

They are expressed as the sum of two harmonics (9.31 years and 10.23 years, see Fig. 4), …

Keeling and Whorf: “Possible forcing of global temperature by the oceanic tides”
http://www.pnas.org/content/94/16/8321.full.pdf‎