AMO Versus the Mid-Latitude North Pacific Residual

The North Atlantic (0 to 81W, 0 to 75N) SST and the Global SST are illustrated in Figure 1. These are the two components of the Atlantic Multidecadal Oscillation (AMO).

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Figure 1

Figure 2 illustrates the North Atlantic SST minus global SST, which is the recipe for calculating the AMO. The effects of the AMO on Northern Hemisphere (North America and Europe) temperatures have been widely studied and documented.

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Figure 2

The third, Figure 3, is a similar comparison of SSTs, but this time the Mid-Latitude North Pacific (20 to 65N) SST is illustrated with Global SST. These are the same mid-latitude coordinates as the Pacific Decadal Oscillation (PDO). Note how the North Pacific variations seem to drive global SST.

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Figure 3

Figure 4 shows the North Pacific SST minus global SST. This simple calculation excludes all the PDO calculation steps outlined in Zhang, Y., J.M. Wallace, D.S. Battisti, 1997: “ENSO-like interdecadal variability: 1900-93”. J. Climate, 10, 1004-1020. In Figure 4, with the global temperature signal removed, what’s left is the Mid-Latitude North Pacific Residual. This curve bears no likeness to the PDO. Note the scale also. The variations in SST are significantly less than the PDO, which is standardized.

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Figure 4

Figure 5 illustrates the relative magnitudes of the AMO and the North Pacific Residual. The North Pacific Residual and the AMO have been in synch to a reasonable extent since 1920. Prior to that, there was an asynchronous period, and, if the areas of the North Atlantic and North Pacific covered by these data sets are close to the same, the change in the Pacific would have outweighed the AMO and driven global temperatures up, beginning in 1909.

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Figure 5

Let’s compare them to the Global Temperature Anomaly. Refer to Figure 6. Isn’t it amazing how that works?

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Figure 6

NOTE REGARDING GLOBAL TEMPERATURE IMPACT

A discussion of the AMO from the RealClimate Glossary:
http://www.realclimate.org/index.php/archives/2004/11/atlantic-multidecadal-oscillation-amo/langswitch_lang/en

“A multidecadal (50-80 year timescale) pattern of North Atlantic ocean-atmosphere variability whose existence has been argued for based on statistical analyses of observational and proxy climate data, and coupled Atmosphere-Ocean General Circulation Model ("AOGCM") simulations. This pattern is believed to describe some of the observed early 20th century (1920s-1930s) high-latitude Northern Hemisphere warming and some, but not all, of the high-latitude warming observed in the late 20th century. The term was introduced in a summary by Kerr (2000) of a study by Delworth and Mann (2000).”

If the AMO describes “some” and “some, but not all,” of the warming observed over the 20th Century, I would think that the combined effects of the AMO and the North Pacific Residual would describe “most” and “most, but not all,” of the warming and cooling over the period of the instrument temperature record. Add the impacts of solar irradiance, ENSO, and volcanic aerosols, and what’s left for AGW?

Sounds like the lead-in for another post. Maybe in the future. There are too many other things hidden away in the ERSST data that need to be attended to first.

CLOSING REMARK

There appears to be a mistaken collective opinion that the PDO represents North Pacific SST anomaly, like the AMO. It does not. The curve if the North Pacific Residual bears little resemblance to the PDO.

SOURCE

Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc