New SST Record Effects on “AMO”

So there is a new record of sea surface temperatures and a clever fellow on the Climate Audit thread says:

Someone should see what effect these changes to the sea surface temperature data have on the calculations of various so called “indices” of “variability”. There could be quite a lot of mis-interpretation of “PDO” and “AMO” etc “signatures” or “patterns” in the data if these things are taken into account. Seeing if it changes the “AMO” will be relatively easy, just using the data available on climate explorer. I’ll see what happens, and perhaps get back to everyone.

Well of course, that clever commenter 😉 was me, and I am happy to oblige myself by examining this issue. The data, along with many climate datasets, is conveniently available here. Which is good because I have a hard time using the Hadley website some times. The region of Atlantic Sea Surface Temperatures involve is from the equator to 70 degrees North latitude, and 80 to zero West longitude (-80 East to zero East). I got these SST for both the old HADSST2 and new HADSST3 data so I am comparing old apples to new apples. I calculated the differences (ie, the “corrections” that had been applied) I then calculated the AMO from the old data (ie detrended) and also another AMO which was the same data, but with the differences added in (zero after 2006 since no corrected data are yet available, and the differences towards the end are very small anyway. The three (HADSST2 AMO, HADSST3-HADSST2 data from the region, and HADSST2 AMO + “correction”) were then calculated as 12 month moving averages to eliminate the monthly noise that obscures the ability to discern what is going on. Here is what you get:

It looks to me like this may make the AMO data if HADSST is used more closely resemble the AMO calculated using Kaplan’s dataset, the differences previously looked like this, according to Bob Tisdale.

Anyway, make of it what you will, it looks to me like the “AMO” is indeed somewhat altered by this, but not hugely. The “PDO” will be another story, something for someone else to look at, I think.


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