Graham, sorry I don't follow that. I understand how a dipole is detected, which is looking for correlations that approach -1, but not the link strength. I hope I am not leading people astray by my confusion.

I keep thinking that correlations on very short time scales are indistinguishable from autocorrelation. Pick a location just outside the NINO34 region and any autocorrelation in the NINO34 region can easily leak into the outer regions. But how do you exclude that or determine a cutoff region?