Iirc it's been suggested that there my be at least 3 flavours of El Ninos. Are central El Ninos as periodic as eastern ones? The Californian blocking behaviour seems similar to blocking of the NH jet stream (the 'arctic vortex').
Perhaps there is only one dipole and some aperiodic phenomenon modifies it?
I'd love to visualise the data for the ocean conveyor and how it's changed since the deeper ocean buoys were deployed. Dara, did you download any of the Argo data?