Guest post by Bob Tisdale
INTRODUCTION
I’ve written numerous posts that describe the Pacific Decadal Oscillation (PDO), what the PDO represents, and, just as important, what it does not represent. For those new to the PDO and for those needing a refresher, refer to An Introduction To ENSO, AMO, and PDO — Part 3An Introduction To ENSO, AMO, and PDO — Part 3.
IceCap recently published a post about the PDO. One of the illustrations in that post confirms a point I have been making: that the PDO does not represent the Sea Surface Temperatures of the North Pacific. And I’ve added a few additional comments and clarifications about the IceCap post.
In my post An Introduction To ENSO, AMO, and PDO — Part 3, the discussions of the PDO patternwere about the spatial pattern. But the word pattern can also be time-related and, therefore, it could pertain to the PDO’s “behavior in time”. A recent discussion on a blog thread gave me the impression that the multiple meanings of the word pattern could be the cause of some of the confusion about the PDO.
Also, much of the post An Introduction To ENSO, AMO, and PDO — Part 3discussed and illustrated the fact that the PDO does not represent the Sea Surface Temperature Anomalies of the North Pacific. There is another factor that may lead to some of the continued misunderstandings about the PDO. The PDO data is standardized. This could greatly exaggerate the magnitude of its variations. Could the standardization also inflate its perceived importance?
I had also wanted to include the errors in the SkepticalScience post It’s Pacific Decadal Oscillation . The SkepticalScience post was obviously written by someone who never plotted the Sea Surface Temperature anomalies of the North Pacific, who misunderstands how the PDO is calculated and what it represents, and who misunderstands or elects to misrepresent climate oscillations. But this post is long, so I’ll present the Skeptical Science errors in a separate post.
THE ICECAP PDO POST
Figure 1 is a screen cap of the opening of Joe D’Aleo’s post about the PDO at IceCap. I’ve included the screen cap because if you were to click on the post title Is the PDO real or a skeptic inventionat IceCap the link does not bring you to the post; it links to a .pdf document titled “THE PDO.” Most of the IceCap post and the linked .pdf document appear to be the same, but their opening paragraphs and the titles are different.
Figure 1
That aside, most of the IceCap post is intended to confirm the existence of the PDO, which is something I don’t dispute. If you’ve watched any of the SST .gif animations or videos I’ve prepared, the positive and negative PDO spatial patterns are very visible. And they should be; the PDO spatial pattern is the most prevalent of the many that form in the North Pacific SST anomalies. The IceCap post also mentions using the Pacific Decadal Oscillation in weather forecasts. Since there are a number of papers that describe weather patterns associated with the PDO, I imagine the PDO data is a useful index for meteorologists.
But one of the points that I have illustrated and discussed a number of times is that the PDO does not represent the Sea Surface Temperature anomalies of the North Pacific, north of 20N. The IceCap post includes a group of PDO- and ENSO-related maps, Figure 2. And those maps actually illustrate that the PDO does not represent the Sea Surface Temperature (SST) anomalies of the North Pacific.
Figure 2
I’ve modified the illustration, Figure 3, by highlighting the area used to calculate the PDO data and by covering the rest of the maps with text. The PDO is not calculated from the SST data south of 20N, so all of that additional visual information exaggerates the surface area represented by the PDO.
Figure 3
My text in Figure 3 reads: In The Positive (Warm) Phase Map Of The PDO Shown Above Left, The Sea Surface Temperature Anomaly For The North Pacific North Of 20N Appears To Be Negative. That Is, The Negative SST Anomalies Cover A Greater Surface Area And They Are More Intense Than The Positive Anomalies. The Opposite Holds True For The Map On The Right-Hand Side. How Then Could A Positive (Warm) Phase Of The PDO Raise Global Surface Temperatures, And Vice Versa?
Someone is bound to note that the IceCap post does not mention that the PDO has an impact on Global surface temperatures. Agreed. Their post doesn’t. This part of my discussion is about the common belief that the sign of the PDO dictates whether global temperatures rise or fall. Since the sign of the PDO does not represent the Sea Surface Temperature of the North Pacific the belief is unfounded.
In past posts, I’ve presented that there is an inverse relationship between the PDO and the Sea Surface Temperature (SST) Anomalies of the North Pacific. This can be shown with a graph that compares the PDO data and the difference between the SST anomalies of the North Pacific north of 20N and global SST anomalies. For simplicity sake, we’ll use the term “North Pacific Residual” for the data that’s calculated as the North Pacific SST anomalies minus the Global SST anomalies. Refer to Figure 4. We’ll use the North Pacific Residual in the comparison graph because one of the steps taken to calculate the PDO is to subtract Global SST anomalies from the SST anomalies of each 5 degree by 5 degree grid of the North Pacific north of 20N. Both datasets in Figure 4 have been smoothed with 121-month running average filters. Other than the agreement between the multidecadal variations in the two curves, there are a couple of things to note about the graph. First, the PDO data has been inverted; that is, it’s been multiplied by a negative number. Second, the PDO data has also been scaled by a factor of 0.2. That was an arbitrarily chosen round number I used to bring the variations of the PDO down into line with the North Pacific Residual data. But let’s look at the scaling in another way: the multidecadal variations in the PDO data are five times higher than the actual variations in the North Pacific Residual data in that graph. One might conclude the PDO data exaggerates the actual multidecadal variations in North Pacific SST anomalies. More on that later.
Figure 4
Figure 4 is taken from the post An Inverse Relationship Between The PDO And North Pacific SST Anomaly Residuals.
The SST anomaly data for the North Pacific is part of the Global Surface Temperature data, but the PDO data is not. This inverse relationship between the PDO and the SST anomaly data of the North Pacific directly contradicts the assumption that a positive (warm) PDO is responsible a rise in global temperatures or that a negative (cold) PDO is somehow responsible for a drop in global temperatures.
The IceCap post attempts to resurrect the argument that there is no clear evidence that ENSO drives the PDO. IceCap bases their brief discussion on a quote from the 14-year old Mantua et al (1997) paper “A Pacific interdecadal climate oscillation with impacts on salmon production.” The IceCap post reads, “The authors made no claim as to which (PDO or ENSO) was the chicken and which the egg.” And IceCap includes a quote from Mantua et al (1997):
“The ENSO and PDO climate patterns are clearly related, both spatially and temporally, to the extent that the PDO may be viewed as ENSO-like interdecadal climate variability (Tanimoto et al. 1993; ZWB). While it may be tempting to interpret interdecadal climatic shifts as responses to individual (tropical) ENSO events, it seems equally conceivable that the state of the interdecadal PDO constrains the envelope of interannual ENSO variability.”
That paragraph from Mantua et al (1997) appears to contradict a paper they reference. Mantua et al (1997) calculate the PDO using a method that was presented in Zhang et al (1997) ENSO-like Interdecadal Variability: 1900–93. In Zhang et al (1997), the PDO was identified as “NP”, and they use Cold Tongue Index SST anomalies (CT) as the El Niño-Southern Oscillation (ENSO) proxy. Zhang et al (1997) note:
“Figure 7 shows the cross-correlation function between CT and each of the other time series in Fig. 5. The lag is barely perceptible for TP and G and it increases to about a season for G – TP and NP, confirming that on the interannual timescale the remote features in the patterns shown in Fig. 6 are occurring in response to the ENSO cycle rather than as an integral part of it…”
It would be difficult for the PDO to drive ENSO if ENSO leads the PDO by a season and if the PDO spatial pattern is a “response to the ENSO cycle rather than…an integral part of it.”
In the 14 years since Mantua et al (1997) was published, there have been a number of papers that confirm that ENSO drives the PDO. In ENSO-Forced Variability of the Pacific Decadal Oscillation, Newman et al (2004) also found that the PDO lags ENSO. They describe cell d of their Figure 1 as:
“ENSO also leads the PDO index by a few months throughout the year (Fig. 1d), most notably in winter and summer. Simultaneous correlation is lowest in November– March, consistent with Mantua et al. (1997). The lag of maximum correlation ranges from two months in summer (r ~ 0.7) to as much as five months by late winter (r ~ 0.6). During winter and spring, ENSO leads the PDO for well over a year, consistent with reemergence of prior ENSO-forced PDO anomalies. Summer PDO appears to lead ENSO the following winter, but this could be an artifact of the strong persistence of ENSO from summer to winter (r = 0.8), combined with ENSO forcing of the PDO in both summer and winter. Note also that for intervals less than 1yr the lag autocorrelation of the PDO is low when the lag autocorrelation of ENSO (not shown) is also low, through the so-called spring persistence barrier (Torrence and Webster 1998).”
And the first sentence of the Conclusions of Newman et al (2004) reads (their italics):
“The PDO is dependent upon ENSO on all timescales.”
My post An Introduction To ENSO, AMO, and PDO — Part 3 included the same discussions of those two papers under the heading of DOES THE PDO DRIVE ENSO?
A more recent paper, Shakun and Shaman (2009) “Tropical origins of North and South Pacific decadal variability” also confirms that the PDO is an aftereffect of ENSO. In addition to the PDO, they use the acronym PDV for Pacific Decadal Variability.
The Shakun and Shaman (2009) Conclusions read:
“Deriving a Southern Hemisphere equivalent of the PDO index shows that the spatial signature of the PDO can be well explained by the leading mode of SST variability for the South Pacific. Thus, PDV appears to be a basin-wide phenomenon most likely driven from the tropics. Moreover, while it was already known PDV north of the equator could be adequately modeled as a reddened response to ENSO, our results indicate this is true to an even greater extent in the South Pacific.”
These papers confirm my statements from past posts that the PDO is an aftereffect of ENSO. And that brings us to the two tables from the IceCap post, which I have merged into one graphic, Figure 5. IceCap introduces the tables by stating:
“During the positive phase see the dominance of more frequent, stronger, longer La Ninas and the positive PDO mode, more frequent, stronger and longer El Ninos.”
There is an obvious error in that sentence. It should begin with “During the negativephase…”
Figure 5
Now I do realize that IceCap has not stated that the positive PDO is responsible for the more frequent, stronger and longer El Niño events and vice versa, but they implied it. And that contradicts the papers above. Since the PDO is an aftereffect of ENSO, a period when El Niño events dominated would cause the PDO to be positive, and vice versa for epochs when La Niña events dominate.
A SIMPLE DESCRIPTION OF HOW THE PDO SPATIAL PATTERN IS FORMED
To reinforce the discussion above, the following is a simple explanation of the processes that cause the PDO spatial pattern during ENSO events.
A positive PDO spatial pattern is characterized by SST anomalies in the eastern North Pacific that are higher than the SST anomalies in the central and western North Pacific. That positive PDO pattern is created by the response of the North Pacific SST anomalies to an El Niño event. Changes in coupled ocean-atmosphere processes, resulting from the El Niño, can cause an increase in the SST anomalies in the eastern North Pacific. Since the El Niño causes a reversal of trade winds in the western tropical Pacific, less warm water than normal is spun up into the western and central North Pacific (an area called the Kuroshio-Oyashio Extension or KOE), and SST anomalies of the western and central North Pacific drop. The initial drop in the western and central North Pacific is also driven by the changes in coupled ocean-atmosphere processes that are caused by the El Niño. The reverse holds true during a La Niña in the eastern North Pacific. For the western and central North Pacific during a La Niña, the leftover warm water from the El Niño also gets spun up into the KOE, adding to the warm waters being brought there by the increased strength of the trade winds, both of which raise SST anomalies there.
There are differences between the PDO and an ENSO proxy such as NINO3.4 SST anomalies from time to time. (NINO3.4 SST anomalies are a commonly used proxy for the frequency and magnitude of El Niño and La Niña events.) The reason for this is that other factors can impact how the North Pacific SST anomalies respond to ENSO events. These other factors include shifts in sea level pressure in the North Pacific and a phenomenon called The Reemergence Mechanismalong the Kuroshio-Oyashio extension (KOE). Aerosols from explosive volcanic eruptions should also account for some of the differences between the PDO and an ENSO proxy, though I have never seen this discussed in any papers.
CAN THE MULTIPLE MEANINGS OF THE WORD PATTERN ADD TO THE CONFUSION ABOUT THE PDO?
The Joint Institute for the Study of the Atmosphere and Ocean Joint Institute for the Study of the Atmosphere and OceanJoint Institute for the Study of the Atmosphere and Ocean (JISAO) Pacific Decadal Oscillation (PDO) webpage is a primary source for PDO information and data. Two maps are used by JISAO to illustrate the spatial patterns that can exist during the warm and cool phases of the PDO, Figure 6. I’ve highlighted the area of the North Pacific represented by the Pacific Decadal Oscillation. It is the area north of 20N, and only that area. The word “pattern” in the opening paragraph on that webpage refers to the “spatial climate fingerprint” of the North Pacific north of 20N, not the multidecadal variability of its data. As discussed previously in this post, when the PDO data is positive (warm phase), the SST anomalies in the eastern North Pacific are warmer than those in the western and central North Pacific, and when the PDO is negative (cool phase), the SST anomalies in the eastern North Pacific are cooler than the SST anomalies in the western and central north Pacific.
Figure 6
Farther down on the JISAO PDO webpage, the PDO is described as:
The “Pacific Decadal Oscillation” (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. While the two climate oscillations have similar spatial climate fingerprints, they have very different behavior in time.
Again, the word pattern is being used to describe spatial characteristics of the SST anomalies.
As discussed in An Introduction To ENSO, AMO, and PDO — Part 3An Introduction To ENSO, AMO, and PDO — Part 3, the phrase “El Niño-like pattern” does NOT mean that the North Pacific (north of 20N) has a separate El Niño-like event.It refers to the fact that a typical El Niño event creates a spatial pattern in the North Pacific where it is warmer in the east than it is in the central and western portions, and a typical La Niña event will create the opposite pattern, cooler in the east than it is toward the center and west of the North Pacific.
Figure 7 is a time-series graph that compares the PDO and NINO3.4 SST anomalies (a commonly used proxy for the frequency and magnitude of El Niño and La Niña events). Both datasets have been smoothed with a 121-month filter. Keep in mind that the NINO3.4 SST anomalies represent exactly that, the SST anomalies of an area of the tropical Pacific called the NINO3.4 region, which is bordered by the coordinates of 5S-5N, 170W-120W, while the PDO does not represent the SST anomalies of the North Pacific. The PDO is a statistically manufactured dataset. As illustrated, the multidecadal variations in the PDO and the NINO3.4 SST anomalies are different. Both vary from positive to negative in the mid-1940s and rise from negative to positive in the late 1970s, but the NINO3.4 SST anomalies have an extra period of positive values in the 1960s. As discussed earlier in this post, the reason the PDO has a different “behavior in time” is because the PDO is also strongly impacted by other factors, including sea level pressure and volcanic eruptions.
Figure 7
In summary, on the main JISAO Pacific Decadal Oscillation (PDO) webpage, the word pattern always refers to the “spatial” characteristics of the North Pacific SST anomalies, not its behavior in time.
THE WORD PATTERN CAN ALSO BE TIME RELATED
The second illustration on the main JISAO Pacific Decadal Oscillation (PDO) webpage is a time-series graph of the PDO data. It was missing from the website as I prepared this post. But there are copies posted at other websites. Refer to Figure 8.
Figure 8
On their PDO Index Monthly Values webpage, JISAO uses the phrase “the pattern of variability” to describe the PDO’s “behavior in time” or the periodicity of the PDO data. Refer to the description of the dataset at the top of the page. It reads (my boldface):
Updated standardized values for the PDO index, derived as the leading PC of monthly SST anomalies in the North Pacific Ocean, poleward of 20N. The monthly mean global average SST anomalies are removed to separate this pattern of variability from any “global warming” signal that may be present in the data.
The uses of the word pattern are different, and their intents are different. Does the use of the word pattern in both instances add to the confusion about the PDO? I don’t have the answer. I’m asking the question. Clearly, the use of pattern in the JISAO description of “The ‘Pacific Decadal Oscillation’ (PDO) is a long-lived El Niño-like pattern” relates to its spatial characteristics. Likewise, the word pattern in the JISAO description of their maps, “Typical wintertime Sea Surface Temperature (colors), Sea Level Pressure (contours) and surface windstress (arrows) anomaly patternsduring warm and cool phases of PDO,” refers to the same thing, the spatial pattern.
Note: I mentioned above that there are no El Niño or La Niña events in the North Pacific north of 20N. I have shown, however, that there are secondary releases of heat in the North Pacific from the warm waters left over from an El Niño. These secondary releases of heat from the North Pacific occur along the Kuroshio-Oyashio Extension (KOE) and they occur during La Niña events that follow major El Niño events. Refer to The ENSO-Related Variations In Kuroshio-Oyashio Extension (KOE) SST Anomalies And Their Impact On Northern Hemisphere Temperatures.
DOES THE PDO DATA EXAGGERATE ITS RELATIVE SIGNIFICANCE?
Figure 9 compares the Pacific Decadal Oscillation (PDO) data and NINO3.4 SST anomalies. The scales are similar and that might lead one who is unaware of the differences between the two datasets to believe the two “signals” are similar in magnitude. That’s wrong for a number of reasons. First, the NINO3.4 SST anomalies represent the SST anomalies of an area in the equatorial Pacific, but the PDO data does not represent the SST anomalies of the North Pacific. The PDO data is a statistically manufactured dataset that represents an abstract form of the SST data there. Second, the NINO3.4 SST anomalies are presented in Deg C. The PDO data is not. The PDO data has been standardized.
Figure 9
Unfortunately, as far as I know, there is no PDO data available online that has not been standardized. So to illustrate the PDO data before standardization, one would have to duplicate the process JISAO uses to create it. Two of the three SST datasets JISAO uses are obsolete and the differences between those older datasets and the current spatially complete datasets are significant, so the results could be very different. And we really do not need to go through all of that trouble to show that the PDO exaggerates the variability of the North Pacific SST anomalies. We can show that other ways.
The inverse relationship between the PDO and the North Pacific Residual was illustrated in Figure 4. And as you’ll recall, the North Pacific Residual was calculated by subtracting Global SST anomalies from North Pacific SST anomalies, north of 20N. Both datasets in Figure 4 were smoothed with a 121-month running-average filter and the PDO data was scaled and inverted (multiplied by -0.2) to bring its variations into line with the North Pacific Residual data. For the next illustration, Figure 10, let’s leave the PDO data in its raw monthly form, and only invert (multiply by -1) the North Pacific Residual data. That is, we won’t scale either dataset. As shown in Figure 10, the actual variations in the North Pacific Residual are miniscule compared to those of the standardized PDO data.
Figure 10
The standard deviation of the North Pacific Residual data is 0.177, so to standardize that dataset we divide it by that value, or multiply it by its reciprocal of 5.65. Refer to Figure 11. Note how well the inverted and standardized North Pacific Residual data (using a different SST dataset, HADISST) captures the underlying multidecadal variations of the PDO data.
Figure 11
And we can detrend the North Pacific SST anomaly data to also show how the PDO exaggerates actual North Pacific Sea Surface Temperature variability. Again in this example, both datasets are in their “raw” form, and the detrended North Pacific SST anomalies are inverted (multiplied by -1.0). The PDO data as shown in Figure 12 greatly exaggerates the actual variations in the detrended North Pacific SST anomalies.
Figure 12
To standardize the detrended North Pacific SST anomalies, we’ll divide the data by its standard deviation (0.182), or multiply it by its reciprocal of 5.5. Once again, as shown in Figure 13, much of the multidecadal variability of the PDO can be captured by inverting and scaling the adjusted North Pacific SST anomalies.
Figure 13
Whether we present the North Pacific SST anomalies detrended or as a residual, the PDO data exaggerates the actual variations in North Pacific SST anomalies by a factor of at least 5.5. This may also lead to some the misunderstandings of the effects of the PDO on global temperatures.
CLOSING
The PDO is a useful index. Based on the IceCap post, it is used by meteorologists for weather predictions. The early papers about the PDO discussed its impact on salmon production, so it is also useful in those endeavors. But the PDO cannot be used to explain epochs of global warming or cooling because the PDO does not represent a process through which the North Pacific could raise or lower global temperatures.
This post also illustrated how the PDO data is inversely related to North Pacific SST anomalies and how the PDO data greatly exaggerates the actual variations in the Sea Surface Temperatures of the North Pacific.
In a follow-up post, we’ll discuss the error-filled SkepticalScience post It’s Pacific Decadal Oscillation.
SOURCE
The PDO data and the HADISST anomalies presented in this post are available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere
phlogiston says: “You resist the use of the term ‘spatio-temporal pattern’ when its utility here is very compelling, preferring to discuss spatial and temporal pattern separately.”
The intent of the post is to clarify the PDO. Based on a recent discussion with another blogger, I found the multiple meanings of the word pattern, without specifying whether the pattern was spatial or temporal, was causing confusion. I was discussing spatial patterns and the other blogger thought I was referring to temporal patterns. That’s the only reason the subject was raised in this post.
Bob Tisdale says:
July 3, 2011 at 2:36 am
You asked, “How is a negative PDO figure obtained when the majority of the Nth Pacific SST’s are warmer? Is there a factor applied or is the subtraction of the global mean SST’s producing the neg value?”
————————-
There is no inverting factor listed in the description of their calculation.
Your graphs show that the PDO values are very close to inverted Nth Pacific SST’s, but you have not answered my question. Do you have a thorough understanding of how the PDO values are calculated?
btw.. you may need to read back as my comments quite often end up in the sinbin. (the landsch*** connection)
Geoff Sharp: With respect to your July 3, 2011 at 1:43 am comment, which is a response in part to my comment of July 2, 2011 at 4:37 am. In my comment, I suggest that you: start at this comment and read our exchange through the rest of the thread:
http://wattsupwiththat.com/2011/06/17/easterbrook-on-the-potential-demise-of-sunspots/#comment-684763
If you had refreshed your memory by reading that thread, you would not be now making statements that contradict what you’d written about a week ago. I have no plans to go through them point by point to show that your current claims do not reflect the reality of what you wrote a week ago.
You continue to attempt to dispute my findings with unfounded statements, when in reality you have acknowledged that you do not understand how the PDO is calculated and, therefore, don’t understand what it represents.
If you can disprove anything that I’ve written in this post or on this thread, using data instead of baseless claims, I will respond to it. Other than that…
Good-bye, Geoff. I attempted to ignore you earlier. I will try again.
Bob Tisdale says:
July 3, 2011 at 6:47 am
good-bye, Geoff. I attempted to ignore you earlier. I will try again.
A very weak answer Bob. If this is too much for you then I can sympathize, but you have not answered my questions. You have castigated Easterbrook for using an “outdated” PDO scale and then tried to denigrate the PDO as a tool not worthy of substance but put up no reasonable evidence. You have shown no real understanding of how the PDO values are calculated, this should be a mandatory requirement for someone challenging its credibility.
Lets cut thru the crap….I have offered you a challenge on your Figure 7. Lets see the result?
Geoff Sharp: Here’s one last graph for you to consider. I had the KNMI Climate Explorer perform Principal Component analyses of three regions in the Pacific: the North Pacific north of 20N (20N-65N, 100E-100W), the Eastern Tropical Pacific (20S-20N, 180-90W), and NINO3.4 region (5S-5N, 170W-120W). All datasets are detrended. None of the data is standardized. And I’m illustrating the 1st Principal Component for those three regions in the following graph. The variability of the 1st PC North Pacific north of 20N is not in the same ballpark as the Eastern Tropical Pacific and it’s not in the same league as the variability of 1st PC of the NINO3.4 region:
http://i54.tinypic.com/x6cxvo.jpg
Bob Tisdale says:
July 3, 2011 at 8:33 am
Lets cut thru the crap….I have offered you a challenge on your Figure 7. Lets see the result?
Geoff Sharp: Your replies are beyond laughable. You asked me how the PDO was calculated. I provided you with an answer, quoting an email I received from the keeper of the PDO data, Nate Mantua. You advised me that you didn’t understand it and you asked a couple of questions. I linked simpler discussions of how the PDO was calculated and replied to your questions.
And after all of that, now you have the audacity to write, “Your graphs show that the PDO values are very close to inverted Nth Pacific SST’s, but you have not answered my question. Do you have a thorough understanding of how the PDO values are calculated?”
Later you replied, “Lets cut thru the crap….I have offered you a challenge on your Figure 7. Lets see the result?”
Correction, in your earlier comment you made the request, “Rescale the ENSO data on your Figure 7 so that the high and low points match the PDO, then we might see a comparison.” I elected to ignore your request. Now you call it a challenge. Your challenge is based on your failure to grasp the subject at hand, which I’m sure Pamela Grey continues to find entertaining.
I believe in the post above I have repeatedly addressed the fact that the PDO does not represent the SST anomalies of the North Pacific, while the NINO3.4 SST anomalies do represent the SST anomalies of the NINO3.4 region. You even mentioned that the comparison is apples and oranges. Scaling them does not eliminate the fact that they’re still apples and oranges.
Tisdale & Sharp
I have no idea how PDO and ENSO indicies are calculated, but when normalised to the same scale there is a high degree of correlation year in year out.
http://www.vukcevic.talktalk.net/P&E.htm
M.A.Vukcevic says:
July 3, 2011 at 2:18 pm
Thanks Vuk, you have saved me the trouble and eloquently put this argument to rest. Enough said I think.
M.A.Vukcevic says: “I have no idea how PDO and ENSO indicies are calculated, but when normalised to the same scale there is a high degree of correlation year in year out.”
Agreed, and that’s been well known for years, but that’s not the topic of this conversation.
Bob Tisdale says:
July 3, 2011 at 7:27 pm
Agreed, and that’s been well known for years, but that’s not the topic of this conversation.
You just do not know when to lie down. Some excerpts from your article and discussions proves otherwise.
The PDO data is standardized. This could greatly exaggerate the magnitude of its variations. Could the standardization also inflate its perceived importance?
I had also wanted to include the errors in the SkepticalScience post It’s Pacific Decadal Oscillation . The SkepticalScience post was obviously written by someone who never plotted the Sea Surface Temperature anomalies of the North Pacific, who misunderstands how the PDO is calculated and what it represents, and who misunderstands or elects to misrepresent climate oscillations.
One might conclude the PDO data exaggerates the actual multidecadal variations in North Pacific SST anomalies.
Now I do realize that IceCap has not stated that the positive PDO is responsible for the more frequent, stronger and longer El Niño events and vice versa, but they implied it.
Figure 7 is a time-series graph that compares the PDO and NINO3.4 SST anomalies (a commonly used proxy for the frequency and magnitude of El Niño and La Niña events). Both datasets have been smoothed with a 121-month filter. Keep in mind that the NINO3.4 SST anomalies represent exactly that, the SST anomalies of an area of the tropical Pacific called the NINO3.4 region, which is bordered by the coordinates of 5S-5N, 170W-120W, while the PDO does not represent the SST anomalies of the North Pacific. The PDO is a statistically manufactured dataset. As illustrated, the multidecadal variations in the PDO and the NINO3.4 SST anomalies are different.
Third, if the PDO and an ENSO proxy can run out of synch occasionally, then the PDO is truly not a reasonable proxy for ENSO tendencies. You’re better off using an ENSO proxy.
DOES THE PDO DATA EXAGGERATE ITS RELATIVE SIGNIFICANCE?
Figure 9 compares the Pacific Decadal Oscillation (PDO) data and NINO3.4 SST anomalies. The scales are similar and that might lead one who is unaware of the differences between the two datasets to believe the two “signals” are similar in magnitude. That’s wrong for a number of reasons. First, the NINO3.4 SST anomalies represent the SST anomalies of an area in the equatorial Pacific, but the PDO data does not represent the SST anomalies of the North Pacific. The PDO data is a statistically manufactured dataset that represents an abstract form of the SST data there. Second, the NINO3.4 SST anomalies are presented in Deg C. The PDO data is not. The PDO data has been standardized.
But the PDO cannot be used to explain epochs of global warming or cooling because the PDO does not represent a process through which the North Pacific could raise or lower global temperatures.
This post also illustrated how the PDO data is inversely related to North Pacific SST anomalies and how the PDO data greatly exaggerates the actual variations in the Sea Surface Temperatures of the North Pacific.
(your attack on Easterbrook) Arguments about anthropogenic global warming cannot be won by misrepresenting the PDO,
My views about the PDO are based on data. Dr. Easterbrooks views on the PDO are based on his misunderstandings, as are yours.
Last, have you noticed that Easterbrook never responded to my comments about his post at WUWT? It’s been about a week. You on the other hand, based on you unwillingness to accept what is presented by data, will argue, apparently for the sake of highlighting your own failings.
The failure of your article is your assumption that the Nth Pacific SST’s are the PDO. The PDO uses the area north of 20deg in the Pacific as a component of the overall Pacific basin, look at it as a proxy record if your like, or perhaps a bi product of a larger system or dare I say perhaps a driver of what occurs in the central Pacific. Whoever came up with the spatial mechanisms for calculating the PDO should be applauded as it has stood the test of time and meshes beautifully with the ENSO record.
M.A.Vukcevic says:
July 3, 2011 at 2:18 pm
Tisdale & Sharp
I have no idea how PDO and ENSO indicies are calculated, but when normalised to the same scale there is a high degree of correlation year in year out.
http://www.vukcevic.talktalk.net/P&E.htm
Vuk, of special interest relating to your graph. Nearly all La Nina’s are preceded by a cool PDO (warm water near Asia). This is in direct contrast to Bob’s and the Newman et al 2003 position. But if we look at the El Nino position they tend to lead the PDO. You will notice the reference in the article refers to an ENSO/PDO relationship when comparing what comes first. Perhaps the La Nina/PDO comparison is of special interest. La Nina cannot start until the Walker Circulation pump is in action. The pump cannot start unless there is warm water around Asia and your graph supports this assumption.
Bob asks the question how can the PDO affect world temperatures. Your graph shows exactly how this can happen.
Geoff Sharp says: “You just do not know when to lie down. Some excerpts from your article and discussions proves otherwise.”
The only reasons you would believe my discussions prove otherwise is because you don’t understand what you quoted, or you and I are having two different discussions. I’m attempting to illustrate for you that the magnitude of the variations in the SST anomalies and in the 1st Principal Components of the SST anomalies of the NINO3.4 region are far greater than those of the North Pacific. What are you arguing about?
Geoff Sharp says: “Whoever came up with the spatial mechanisms for calculating the PDO should be applauded as it has stood the test of time and meshes beautifully with the ENSO record.”
A major difference between the PDO and ENSO is the magnitude of their variations, which is one of the points of my post that you continue to fail to accept. This can be seen in the graph that you dismissed, which compared the 1st Principal Components of the detrended SST anomalies for the North Pacific, and the eastern Tropical Pacific, and the NINO3.4 region. The variations in the 1st PC of the NINO3.4 region are 5.5 times greater than those of the North Pacific.
http://i54.tinypic.com/x6cxvo.jpg
We can smooth the1st PC of the NINO3.4 region and the 1st PC of the North Pacific datasets and create a graph that was similar to Figure 7 in the post. The relationship continues. The multidecadal variations in ENSO dwarf those of the PDO.
http://i55.tinypic.com/aakjsn.jpg
The same relationship holds true if we switch back to SST anomalies. The variations in NINO3.4 SST anomalies dwarf the detrended North Pacific SST anomalies and the North Pacific residuals, where the North Pacific Residuals are calculated as North Pacific SST anomalies minus Global SST anomalies.
http://i53.tinypic.com/205tauu.jpg
Geoff Sharp: Let’s wrap this up. I have provided papers that show the PDO lags ENSO. I have illustrated that the PDO is inversely related to the SST anomalies of the North Pacific. I have illustrated that the PDO exaggerates the variations in the North Pacific SST anomalies because the PDO is standardized. Further to that, in my July 4, 2011 at 1:32 am comment, I have illustrated that the variations in the 1st Principal Component of the NINO3.4 region are more than five times greater than the 1st Principal Component of the North Pacific, and I have illustrated that the variations in NINO3.4 SST anomalies dwarf the variations in the SST anomalies of the North Pacific.
And on this thread and in the thread of the Easterbrook post, I asked you a very basic question, which you have failed to respond to on both occasions. That question is, through what process does the PDO cause global temperatures to rise and fall? If you cannot answer that question and document the basis for your belief with data, there is no reason to continue this discussion.
I think you need to read back Bob, Vuk’s graph and my response to it blow every weak point you have tried to raise in this article as well as answering your last question with basic accepted ENSO knowledge. I believe you have sided with the AGW crew and continue to argue along their predictable lines and references.
I don’t need to have discussions with you but I will continue to appose your AGW views when presented. Let’s see if your man enough to approve my comments on your blog?
Geoff Sharp: Regarding your latest conjecture on how climate and ENSO works that you expressed in your July 4, 2011 at 12:59 am comment, it is based on your assumptions and therefore riddled with errors. When you have a hypothesis, always check the satellite-era SST data first, because that’s the epoch with the most spatially complete source data. First, the SST anomalies of the Western and Central Pacific (Kuroshio-Oyashio Extension or KOE) are not the PDO. They are a component of the PDO. Second, the NINO3.4 SST anomalies precede KOE SST anomalies most often during the transition from El Niño to La Niña.
http://i52.tinypic.com/28jcsv4.jpg
FYI, I discussed the ENSO-caused variations in the KOE SST anomalies and their impact on Global Surface Temperatures in the following post:
http://bobtisdale.wordpress.com/2010/12/08/the-enso-related-variations-in-kuroshio-oyashio-extension-koe-sst-anomalies-and-their-impact-on-northern-hemisphere-temperatures/
Second, by your own description, you confirmed what I have said and illustrated in my post. When the PDO is negative, the SST anomalies of the KOE are positive, and since this has a greater impact on North Pacific SST anomalies than the cooling in the east, the North Pacific SST anomalies will rise.
Your attempts to disprove my post have once again failed.
Geoff Sharp says (July 4, 2011 at 2:23 am ): “I think you need to read back Bob, Vuk’s graph and my response to it blow every weak point you have tried to raise in this article as well as answering your last question with basic accepted ENSO knowledge.”
Whose “basic accepted ENSO knowledge”? Yours? You have demonstrated little “basic accepted…knowledge” on even the simplest subjects. You have expressed no knowledge of ENSO. Also, I have addressed the failings in your response to M.A.Vukcevic’s graph.
You continued, “I believe you have sided with the AGW crew and continue to argue along their predictable lines and references,” and you closed with, “I don’t need to have discussions with you but I will continue to appose your AGW views when presented.”
I do not present AGW views. If I did, Anthony Watts would not continue to cross post me here at WUWT. Your failure to understand the difference between my arguments and those of AGW proponents, your failure to recall my history of posts that undermine the AGW hypothesis, and your need to attempt to claim that I have AGW views broadcast the weaknesses of your arguments. Your comments really are laughable, Geoff.
You concluded, “Let’s see if your man enough to approve my comments on your blog?”
Why would I approve the comments of a troll? You have no understanding of the topics being discussed. Your arguments are not based on data, and when confronted with data, you attempt to spin, fabricate, misdirect, and redirect.
Geoff, I’ve taken the time to go back and review some of the points you attempted to make earlier on this thread.
Geoff Sharp says (July 3, 2011 at 1:43 am): “Your evidence is weak, one stating that PDO leads ENSO during the summer.”
You took the discussion out of context. Newman et al wrote in full, “Summer PDO appears to lead ENSO the following winter, but this could be an artifact of the strong persistence of ENSO from summer to winter (r = 0.8), combined with ENSO forcing of the PDO in both summer and winter. Note also that for intervals less than 1yr the lag autocorrelation of the PDO is low when the lag autocorrelation of ENSO (not shown) is also low, through the so-called spring persistence barrier (Torrence and Webster 1998).”
You continued, “What is becoming increasing obvious is your incorrect statement that is often repeated ‘. The PDO does not represent the SST anomalies of the North Pacific.’ It clearly does represent the SST anomalies but using the reverse sign. You wording is misleading and should be amended. The Nth Pacific SST’s are used as a flag to show the reverse is happening at the equator, your own graphs shows that?”
My wording is not misleading, Geoff. My statement, the PDO does not represent the SST anomalies of the North Pacific, does not conflict with my other statements that the PDO is inversely related to the North Pacific SST anomalies, or inversely to the detrended North Pacific SST anomalies, or inversely related to the North Pacific Residuals.
You continued, “The PDO continues to be a valid tool which is made from Nth Pacific SST’s that reflect the pacific basin…”
Incorrect. The PDO is the product of a Principal Component analysis of the North Pacific north of 20N, and only that area. It represents nothing else in the Pacific basin.
Geoff Sharp says (July 3, 2011 at 7:32 am ): “You have castigated Easterbrook for using an ‘outdated’ PDO scale…”
This is a blatant fabrication, Geoff. I clearly stated in my Easterbrook post, “Arguments about anthropogenic global warming cannot be won by misrepresenting the PDO, or by using outdated TSI data, or by creating unusual global temperature anomaly graphs that are obviously wrong to anyone familiar with the instrument temperature record.” Outdated referred to TSI data, not the PDO data.
You continued, “…and then tried to denigrate the PDO as a tool not worthy of substance but put up no reasonable evidence.”
I have discussed why the PDO is a useful tool in the post, Geoff, so that statement clearly misrepresents my record. And the reason you do not find the evidence to be reasonable is because you either do not understand what is presented or you simply elect not accept it due to your tunnel vision.
You continued, “You have shown no real understanding of how the PDO values are calculated, this should be a mandatory requirement for someone challenging its credibility.”
This is another falsehood on your part, Geoff. I have provided you with the description of the method JISAO uses to calculate the PDO. You acknowledged that you didn’t understand parts of it. Additionally, using the KNMI Climate Explorer, I have replicated the PDO in standardized and in un-standardized forms. The record on this thread clearly indicates that you purposely ignored those graphs.
Your false claim that I have AGW views has reduced your arguments to the nonsense level, and I no longer have the need to respond to you on this or any other thread.
Good-bye, Geoff.
REPLY: Geoff, take that as a “thread closed” to further discussion on this matter. I’m rather disappointed in the way you’ve been behaving. So at this point, just walk away and stick to the solar cycle issues – Anthony
Geoff Sharp wrote (July 3, 2011 at 9:16 pm) “Whoever came up with the spatial mechanisms for calculating the PDO should be applauded as it has stood the test of time and meshes beautifully with the ENSO record.”
Geoff, here you are making it crystal clear that you don’t understand how factor analysis (e.g. PCA, EOF, SSA) calculations work. The PDO as defined COULD NOT POSSIBLY AVOID looking like ENSO — and this is an INCREDIBLY trivial point for anyone who understands factor analysis.
I recommend Johnson & Wichern’s textbook on applied multivariate statistical analysis as a starting point. As a prerequisite for reading that textbook one needs a solid understanding of advanced regression analysis.
—
Richard Holle, Thanks for your comments.
Stream of thought of reader ALMOST getting what Bob is saying:
“NHT is a function of North Pacific SST.
PDO is a function of North Pacific SST.
Could North Pacific SST be the long-sought intermediary between PDO and NHT???…
Global T is a function of North Pacific SST.
PDO is a function of North Pacific SST.
Could North Pacific SST be the long-sought intermediary between PDO and global T???…
Naaaawwww! That CAN’T (!) be right.”
–
Easier to bury heads in sand than face disconcerting affirmatives.
M A Vukcevic: Sorry it took so long for me to take a better look at the graph you presented. My earlier reply was simply a response to what you’d written and not the graph.
You wrote, “I have no idea how PDO and ENSO indicies are calculated, but when normalised to the same scale there is a high degree of correlation year in year out.
http://www.vukcevic.talktalk.net/P&E.htm”
You’ve presented two obscure datasets.
Your PDO data is based on ERSST.v3b data:
ftp://eclipse.ncdc.noaa.gov/pub/ersstv3b/pdo/pdo.1854.latest.situ.v3b.ts
There are some differences between it and the more widely referred to JISAO version of the PDO data.
And your ENSO Index link includes data for the Global-SST ENSO index:
http://jisao.washington.edu/datasets/globalsstenso/globalsstenso18002010
The parent page is here:
http://jisao.washington.edu/data/globalsstenso/
The Global-SST ENSO index is calculated as the average SST anomaly equatorward of 20-degrees latitude (north and south) minus the average SST poleward of 20-degrees. That’s really obscure. Our discussion here has been about the commonly used NINO3.4 SST anomalies for an ENSO proxy, and I’m afraid the two obscure indices you use have led to some strange theories by another blogger.
Mr. Tisdale
When I posted the graph,
http://www.vukcevic.talktalk.net/P&E.htm
I only briefly scanned trough the posts, not realising intensity of the exchange .
I do not understand in depth the physical background of either the ENSO or PDO. I just look into available data from respectable institutions, in this case NOAA and University of Washington, assuming that data are authentic and in a legitimate use by the climate science. My only interest is in good correlation of the above data with my privately assembled datasets referring to non-climatic processes of the North and Equatorial Pacific.
BTW. Dr J. Curry suggested elsewhere that both the PDO and ENSO data prior 1950’s are partly reconstructions and as such may not be absolute.
Note: I am limiting my posting to no more than 1-2 / day on average.
M.A.Vukcevic: I agree with Judith Curry. Everyone has to be wary of the early years of any SST-based dataset–actually any surface temperature dataset–due to the poor spatial coverage.
But I thank you for reintroducing me to that curious Global-SST ENSO index. It appears to have been first developed in the early 1990s, and with how it’s created, I’m still trying to determine why the researchers thought it might have been a worthwhile ENSO Index. I’m thinking of writing a post about it.
Regards
M.A.Vukcevic wrote (July 4, 2011 at 10:22 am) “Dr J. Curry suggested elsewhere that both the PDO and ENSO data prior 1950’s are partly reconstructions and as such may not be absolute.”
Huge topic. Properly interpreting some aspects of the early PDO record could involve truly monumental diagnostics exercises.
In many of the indices we discuss there are strong early-record seasonal peculiarities that precisely match strong excursions in the Earth Orientation Parameter (EOP) records. The Climate & EOP communities haven’t made a satisfying effort to integrate knowledge across disciplines. A lot of the work that needs to be done is incredibly tedious, but there is the potential to answer some very interesting questions.
Bob Tisdale wrote (July 4, 2011 at 9:25 am) “[…] Global-SST ENSO index is calculated as the average SST anomaly equatorward of 20-degrees latitude (north and south) minus the average SST poleward of 20-degrees.”
Bob Tisdale added (July 4, 2011 at 4:03 pm) “[…] thinking of writing a post about it.”
Sounds worthwhile and quite interesting.
Yes, I read that, Bob. They still don’t know what comes first. Its the chicken and egg scenario as they stated between trade winds and ocean temps. Is there a coupling? Sure but the chicken is the air pressure IMO. Not looking for a squabble. If they don’t know for sure, then its moot to argue about it. My gut tells me weather (high pressure position and strength).
Brian D says: “Yes, I read that, Bob. They still don’t know what comes first. Its the chicken and egg scenario as they stated between trade winds and ocean temps. Is there a coupling? Sure but the chicken is the air pressure IMO. Not looking for a squabble.”
I’m not squabbling, just discussing. I’m also not disagreeing with you completely.
As Bill Kessler described, the pressure difference would not exist without the Sea Surface Temperature difference, so under “normal” conditions, how could sea level pressure be the chicken? On the other hand, the SST difference wouldn’t exist without the sea level pressure difference.
A relaxation of the trade winds intitiates the El Nino, so in that regard, the chicken would be sea level pressure? But on the other hand, the La Nina phase (after an El Nino) is said to start with the formation of a Rossby wave at approximately 10N in the eastern tropical Pacific (It carries the leftover warm water back to the western Pacific). And the Rossby wave is a coupled phenomenon.
And of course, those explanations pertained to typical events. If memory serves me well, much of the uncertainty in Kessler’s discussion had to do with the fact that different factors can initiate ENSO events, so we’re back at square one.
Regards