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The PDO is NOT a Simple Residual Like the AMO.

People understand the Atlantic Multidecadal Oscillation (AMO). It’s calculated very simply; subtract Global SST (sea surface temperature) anomalies from the North Atlantic SST anomalies. This simple process has been said to remove the global warming signal from the AMO. Many people believe the Pacific Decadal Oscillation (PDO) is calculated using the same basic equation, but it’s not. According to Nathan Mantua of JISAO, the details of how the PDO is calculated are found in this paper:

ENSO-like Interdecadal Variability: 1900–93

Calculating the PDO is a multistep process. It includes creating an SST anomaly time series for each 5 degree grid of the North Pacific (North of 20N), calculating the residual for each grid, and computing the EOFs ( empirical
orthogonal function) of these North Pacific residual SST anomaly fields. The PDO index is the leading PC (principal component) of that analysis. It’s far from a simple process.

The PDO has been found to be a function of ENSO. In “ENSO-Forced Variability of the Pacific Decadal Oscillation“, Newman et al state in the conclusions, “The PDO is dependent upon ENSO on all timescales.”

A few months ago, I discovered the instructions for retrieving Smith and Reynolds ERSST.v2 data (extended reconstructed SST) from the NOAA NOMADS system based on user selected dates and global coordinates:

http://www.ncdc.noaa.gov/oa/climate/research/sst/ERSST-ts.txt

One of the first data sets I downloaded was the time series of SST anomalies for the North Pacific, 20 to 65N, what I called the Mid-Latitude North Pacific SST Anomaly in the following graph. Note the 0.9 deg C drop then rebound in temperature from the late 19th to the mid-20th centuries. It’s tough to miss. It certainly appears to be related to Meridional Overturning Circulation (MOC), not ENSO.

http://i25.tinypic.com/2cyg07k.jpg

Using the same simple process employed to calculate the AMO, that is, subtracting the Global SST Anomaly from the Mid-Latitude North Pacific Anomaly, provides a data set that I’ve dubbed the North Pacific Residual.

http://i28.tinypic.com/jrwjk6.jpg

The North Pacific Residual bears no resemblance to the PDO. In fact, note that I had to scale the PDO to bring it back into line with the data set from which it is extracted. (The PDO data illustrated is from the ERSST.v2 data set, not the JISAO version. The curves of the two PDO data sets are similar, but the ERSST.v2 data extends further back in time.)

http://i27.tinypic.com/2n1sv49.jpg

When compared to the AMO, the two Northern Hemisphere SST oscillations complement one another from the 1920s to present. Prior to that, they were out of synch, offsetting their individual impacts on global temperature. It is no coincidence that Northern Hemisphere and global temperatures follow the rises and falls of these two residual anomalies.

http://i30.tinypic.com/11kv7r5.jpg

CLOSING
Past studies have estimated the contribution of the AMO to the rises and falls of Northern Hemisphere and Global temperatures over the 20th century. I would think that the North Pacific Residual would contribute similarly. Shouldn’t climatologists and climate change bloggers have another index of North Pacific temperature anomalies, one that could be used to determine the effect of the North Pacific SST oscillation on Northern Hemisphere and Global temperatures?

SOURCES

The links and graphs are from my series on Smith and Reynolds SST data:

http://bobtisdale.blogspot.com/2008/06/smith-and-reynolds-sst-posts.html

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

Bob Tisdale

David Stockwell has analysed the CSIRO/BoM Drought Report using data reluctantly released by CSIRO in response to public pressure. His report is entitled: ‘Tests of Regional Climate Model Validity in the Drought Exceptional Circumstances Report’

The Abstract states:

In a statistical re-analysis of the data from the Drought Exceptional Circumstances Report, all climate models failed standard internal validation tests for regional droughted area in Australia over the last century. The most worrying failure was that simulations showed increases in droughted area over the last century in all regions, while the observed trends in drought decreased in five of the seven regions identified in the CSIRO/Bureau of Meteorology report. Therefore there is no credible basis for the claims of increasing frequency of Exceptional Circumstances declarations made in the report. These results are consistent with other studies finding lack of adequate validation in global warming effects modeling, and lack of skill of climate models at the regional scale.

Read David’s own blog here.

Climate Audit:

Stockwell on CSIRO Drought Report

Some Quick Thoughts on CSIRO Drought Info

CSIRO: A Limited Hang out??

CSIRO and Stock Promotions

CSIRO adopts Phil Jones’ Stonewall Tactic

Malcolm Hill alerted me to Cohenite’s comments that are worthy of a new thread:

I’m just a middle man connecting the points first raised by John McLean and Thomas Quirk in their paper, ‘ Australian Temperature Variations – An Alternative View:’

http://mclean.ch/climate/Aust_temps_alt_view.pdf

And Bob Tisdales work with Pacific Decadal Oscillation (PDO)

I agree with Malcolm that this is a crucial issue because if there has been no temperature increase then AGW is shot to bits.

A starting point would be a graph of PDO phase shifts over the 20th Century;

http://wattsupwiththat.files.wordpress.com/2008/04/pdo_monthly.png

There were 3 PDO’s during the 20thC; a warm and dry +ve PDO from 1905-46; a cool and wet -ve PDO from 1946-76; and another +ve PDO from 1976-2006.

A typical temperature chart of the 20th Century is as follows;

http://i32.tinypic.com/2s01m5y.jpg

The 2 upward trends at the beginning and end of the 20th Century are typical because they are similar +ve PDO’s with similar temperature regimes; if one looks at the slope and amplitude for the temperature increase at the beginning, it is identical to the one from 1977 onwards; the only difference is that the one at the beginning of the 20th Century starts from a lower base. The reason for this is not because the temperatures were lower, but because of base period bias. HadCrut uses a base period of 1961-90. This period covers the end of the middle -ve PDO and the beginning of the 2nd +PDO; an average of the 30 years of this base will cause temperatures in the 2nd +PDO period to be anomalously higher because these temperatures will not have the impact of the cooler temperatures of the base period dragging them down as occurred in the averaging process; conversely, the temperatures in the -ve PDO from 1946 onwards will be anomalously cooler because they do not have the averaging benefit of the +ve PDO temperatures; there will be, therefore a step-up in temperature after 1977 and a step-down before 1946. The base period weighting for Hadcrut is 0.15C, which would drag the temperatures of the 2nd +ve PDO back down slightly; but the weighting doesn’t prevent the step-up at 1977 or the step-down at 1946.

What Bob Tisdale has done is to remove the base period bias; he does this by the simple method of annual variance; Tn+1-Tn over the full range of the HadCrut data; the result is this;

http://i25.tinypic.com/e6zj0l.jpg

This shows only variance within the PDO climate; if there was a seperate anthropogenic signal based on increasing CO2 increases it would show as an increasing trend; there is no seperate upward temperature trend, so there is no CO2 caused temperature increase; a comparison between the 2 temperature histories is here;

http://i26.tinypic.com/2hmpw6r.jpg

It is interesting that Lucia has undertaken something similar, but from an opposite direction, when she removed the ENSO signal from all temperature indices in the post 2000 period;

http://rankexploits.com/musings/wp-content/uploads/2008/07/ipcc-falsifies-gavin.gif

That Lucia shows a cooling trend would tend to suggest that if there is an anthropogenic signal, it is a cooling one.