Graham: how did you first find this Niño 3.4 data, and why did you choose to work with it?
I can't find it here:
* Monthly atmospheric and SST indices, NCEP-NOAA, [http://www.cpc.ncep.noaa.gov/data/indices/](http://www.cpc.ncep.noaa.gov/data/indices/)
a website that lists a variety of indices including Niño 3.4. I'm curious because the data you're using may have been "detrended" in some way, and Ludescher _et al_ don't seem to say where they got their Niño 3.4 data.