I think this is a possible direction to go, based on some very promising results that I worked on over the past day.



For all I know, this may be a well known correlation, but I discovered that the tidal gauge data in Sydney Harbor aligns with the SOI behavior remarkably well, especially if a delay differencing of about 2 years is applied.

![ddmodel](http://imagizer.imageshack.us/a/img538/1953/itXH4n.gif)

The tidal data itself has a significant annual and bi-annual periodicity modulated by an erratic envelope, potentially modeled by a DiffEq as shown below.

![sydney](http://imagizer.imageshack.us/a/img537/4346/PDtZKc.gif)


Another interesting teleconnection to consider !

Paul Pukite