PDO — ENSO, Aleutian Low, or some of each?
Guest Post by Basil Copeland
Introduction
In a recent post here at WUWT, as well as on his own blog, Bob Tisdale challenged the popular view that the Pacific Decadal Oscillation (PDO) is a principal driver of climate independent of the tropical El Nino-Southern Oscillation (ENSO) system. Presenting the results of his own analysis, as well as citations from published scientific literature, Bob at least made the case for some plausible relationship between PDO and ENSO. But what is the nature of this relationship, and does it reduce PDO to, as Bob put it, merely “a pattern of SST variability, not SST” itself?
Bob quoted extensively from Newman et al. (2003). While this paper was in press at the time, it was reviewed and considered by Miller et al. (2004). The latter is a comprehensive review of “Decadal-Scale Climate and Ecosystem Interactions in the North Pacific Ocean” (e.g., the title of the paper). While acknowledging a tropical forcing (ENSO) on North Pacific SSTs, they contend that there is another, distinct forcing that is independent of the tropical forcing, related on decadal time scales to the behavior of the Aleutian Low.
In this post I will be citing selected portions of the Miller et al. paper, and presenting some simple empirical data that demonstrate the complex reality of the PDO. While on an interannual to decadal scale it is possible to demonstrate a “teleconnection” between ENSO and the PDO, on multi-decadal time scales this teleconnection appears to have little power to explain the behavior of the PDO. Instead, the multi-decadal pattern of the PDO is based — or “forced” — on midlatitude climate variability reflected in the behavior of the Aleutian Low. Specifically, I will bring into the discussion the North Pacific Index (NPI). The NPI is calculated as the area-weighted sea level pressure over the region 30°N-65°N, 160°E-140°W, and provides a measure of the intensity of the wintertime Aleutian Low. I’ve taken the monthly NPI data, created a moving average, and have normalized and inverted it so that it scales similarly to ENSO and the PDO for purposes of comparison. For ENSO, I am using a series for Nino 3.4. All data sources are cited in a reference list at the end of this post.
Power Spectrum: Nino 3.1, PDO, and NPI
In leading up to a discussion of Newman et al., Miller et al. say:
Deterministic forcing from the tropics clearly has an effect in establishing decadal SST variability in the midlatitudes. The forcing of the canonical SST pattern (around the subtropic front) has long been linked to atmospheric teleconnections from the El Nino/Southern Oscillation (ENSO) events on interannual timescales. (Except as noted, citations will be eliminated in quoting from Miller et al.)
So this much is consistent with the point Bob was making about ENSO being a driver of the PDO, and is what we see in Figure 1 with the common periodicities at 4.8 to 6.5 years, and possibly at ~9 years. But Miller et al. go on to discuss a second pattern of SST’s present in the PDO that have their origin in the Aleutian Low and propagate via “Rossby waves from the central North to the region around the subartic frontal zone and the Kuroshio-Oyashio Extension (KOE) region.” In further describing these Rossby waves, they write:
These Rossby waves arrive several years after the Aleutian Low changes, resulting in a lagged response in SST in the KOE region. This second SST pattern…also projects onto the PDO although it has a lagged relationship to the canonical pattern of SST [i.e. the pattern induced by ENSO]. Hence, the PDO index should be considered an amalgam of these two physical ocean responses. (Emphasis supplied.)
Continuing the first quote above, Miller et al. go on to say:
The forcing of the KOE SST pattern (around the subartic front) is only weakly linked to tropical teleconnections. The independent behavior of the KOE SST has been clarified through its enhanced decadal variance relative to the canonical SST pattern and through its links to decadal wind-stress curl forcing.
Then they comment on Newman et al.:
Recent studies with a simple first-order Markov model with forcing specified by the tropical SST index, damping rate specified by SST persistence (with re-emergence) and white noise forcing (simulating midlatitude weather) reversals that the bulk of the PDO index is explicable by atmospheric forcing from tropical teleconnections (Newman et al., 2003).
Again, this accords with what Bob was saying. But Miller et al. go on to say:
The forcing with tropical origins clearly drives the canonical SST pattern portion of the PDO. However, the simple model result is somewhat deficient in decadal timescale energy. This suggests that the KOE SST pattern portion of the PDO is not simply driven by (or at least is not in phase with) this tropical forcing.
We see this clearly in Figure 1. Out beyond 12.8 years, there is very little power in the Nino 3.4 spectrum. There is modest power on a scale of 31.2 years, but there is simply nothing to compare to the multi-decadal power spectrum seen in the PDO and evident in the NPI. The latter show power at bidecadal, and especially at pentadecadal periodicities. On the latter, I would here just reference a series of papers by Minobe (sometimes with others); see the reference list at the end of this post for examples.
The bottom line? While ENSO forced variation may drive the PDO out to decadal time scales, it does not fully account for PDO variation on longer time scales. That latter is more likely related to long term, low frequency, oscillations in the behavior of the Aleutian Low, which set up what is really the more uniquely characteristic pattern of the PDO: its variation between cool and warm phases on a scale of 20-30 years.
What Difference Does It Make?
Based on discussions we had in comments to his post, and some private email correspondence, I do not think that Bob would have any significant disagreement with any of this. So what was his point, and why do I think it is important to clarify the matter? Bob’s point was that “global warming” cannot be attributed to the PDO. And depending on what one means by “global warming,” he is no doubt correct. That is, if by “global warming” we are speaking of the long rise in global temperatures since the earth came out of the “Little Ice Age,” then certainly, the PDO cannot likely account for that. After all, the PDO is basically an oscillation about the long term global trend, whatever that is. But if by “global warming” we were to mean calling attention to the increase in the rate of increase in global temperatures since the middle of the 20th century — and this was a cornerstone focus of the IPCC’s AR4 — then the behavior of the PDO does become extremely relevant to the so-called “global warming” of the past half century or so.
To understand my point, consider Figures 2 and 3. In Figure 2 I show smoothed trends for the NPI, PDO and Nino 3.4. These were derived using Hodrick-Prescott filtering. Since first introducing this technique to WUWT users last year, I’ve continued to investigate the properties of this technique. As some readers may recall, the outcome all depends upon the value of the “smoothing parameter” lambda. By analyzing Morelet wavelet transforms before and after smoothing, I can determine the degree of smoothing implicit in a given value of lambda. For Figure 2 I used a value of lambda (512000) which results in a degree of smoothing that filters out cycles of less than ~2^6 months, i.e ~5.3 years. It thus captures the decadal (and longer) variation in these three series, while filtering out shorter term periodicities (which are much more prevalent in ENSO than in the PDO/NPI). We can clearly see the decadal variation in ENSO, as well as the multi-decadal variation in the PDO, which is closely matched by the multi-decadal pattern of the NPI, in Figure 2.
I then extracted the first principal component from these three series, shown in Figure 3. Consider this a “weighted average” of the three series. It really does not reveal anything we do not already know – that the PDO/NPI, and a decadal influence from ENSO – has undergone major epoch changes, or regime shifts, in the 20th Century. Figure 3 simply illustrates what is cited on the JISAO web page for the PDO:
Several independent studies find evidence for just two full PDO cycles in the past century: “cool” PDO regimes prevailed from 1890-1924 and again from 1947-1976, while “warm” PDO regimes dominated from 1925-1946 and from 1977 through (at least) the mid-1990’s. Shoshiro Minobe has shown that 20th century PDO fluctuations were most energetic in two general periodicities, one from 15-to-25 years, and the other from 50-to-70 years.
The issue with respect to what impact this has on measuring the degree of “global warming” is obvious. If we simply bifurcate the 20th Century into two halves, which is more or less what the IPCC AR4 did in its assessment of 20th Century global temperature trends, the trend for the second half of the 20th Century is going to begin during a period that was dominated by a cool phase of the PDO, and end during a period dominated by a warm phase. In other words, even if the PDO is not itself, over a complete cycle, contributing to “global warming,” trends calculated this way will be biased upwards because of the transient impact of decadal and bidecadal influences of the PDO on global temperature. Measuring global warming with a starting point in the middle of the 20th Century, which is what the IPCC did in AR4, is just a variation on the theme of cherry picking, something familiar to most WUWT readers.
Perhaps a better way to look at all of this is from the global perspective of Figure 4. Figure 4 plots the HadCRUT3 series from 1850:01 through 2009:03. Shown is a smoothed trend line, blue (HP smoothing, lambda 512000), and superimposed is a smoothed trend line in red (again, HP smoothing with lambda 512000) of the UAH satellite record, rescaled to track with HadCRUT3. In this data, there appear to be two complete PDO-like cycles, when measured peak-to-peak: one from 1879 to 1941, and the other from 1942 to 2004. From 1879 to 1941, the decadal rate of growth in global temperature was 0.036°C/decade; from 1942 to 2004, the decadal rate of growth in global temperature was 0.087°C/decade. Contrast this latter with the claim in IPCC AR4 that the rate of warming for the past 50 years (1956-2005) was 0.13°C/decade.
Put differently, the real rate of warming since the last peak of the PDO is approximately 33% less than alleged by the IPCC because of the bias created in not taking into effect the suppression of global temperatures in the mid-20th by the cool phase of the PDO. So while the PDO itself may not be contributing to global warming, the warm phase of the past three decades, following on two to three decades of a previous cool phase, has allowed climate alarmists to overstate the actual degree of global warming in the 20th Century.
References and Data
- The NPI data I utilized is here: http://www.cgd.ucar.edu/cas/jhurrell/indices.data.html#npmon
- The main page for the PDO data is here: http://jisao.washington.edu/pdo/PDO.latest
I downloaded the data, though, from Wood For Trees: http://www.woodfortrees.org/data/jisao-pdo
- The Nino 3.4 series I used is here: http://climexp.knmi.nl/data/ihadisst1_nino3.4a.dat
- A full cite to the Miller et al., 2004 paper: Miller, AJ, Chai, F, Chiba, S, Joisan, JR and Neilson, DJ. Decadal-Scale Climate and Ecosystem Interactions in the North Pacific Ocean. Journal of Oceanography, Vol. 60, pp. 163 to 188, 2004. A copy can be downloaded here: http://horizon.ucsd.edu/miller/download/jgofs/JO_60-1-11.pdf . I believe many WUWT readers will enjoy this paper. The authors at least acknowledge the role of solar forcing, and cite Landscheidt, Svensmark and Friis-Christensen, and others who are often ignored in articles of this nature.
- The principle paper by Shoshiro Minobe on the pentadecadal cycle in the PDO is “Resonance in bidecadal and pentadecadal climate oscillations over the North Pacific : Role in climatic regime shifts,” Geophysical Research Letters. 26(7), 1999, 855-858. A copy can be downloaded here: http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/21813/1/1999grl_letter.pdf . There is an intriguing indication that Minobe is working on research that would connect the Pentadecadal oscillation to LOD here: http://wwwoa.ees.hokudai.ac.jp/~mikeda/proj/iarc/sympo/8minobe.htm .
- The HadCRUT3 data was downloaded via Wood For Trees: http://www.woodfortrees.org/data/hadcrut3gl .
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John F. Hultquist (09:53:32)
“My thought is we are accustomed to thinking of things as being independent or dependent variables – “ENSO drives PDO, and the like” – while, in fact, nature is more complex, with lots of co-dependencies. Sort of like a spider’s web – tweak it on any line, node, or connection and the whole thing responds”
I agree with you. There is a tendency to try to find short cuts to answers. But it doesn’t work that way.
I like this viewpoint of Richard Feynman :
Adam perhaps instead of clouds a more immediate driver would be the difference in albedo from ice and snow. A cool PDO has warm SSTs in the western Pacific and a warm one has the warm SSTs in the eastern Pacific. With predominant easterly winds, during the cool phase warm waters heat the air which then blow across open ocean having little effect and during the warm phase the water warms air which then blows across N. America reducing the amount of ice and snow cover thereby reducing albedo.
Basil: I haven’t been ignoring your post. I believe I must have I forgotten to press “Submit Comment” with my first comment before I closed the window. Or with the links, it’s awaiting moderation. Either way, I’ll try again.
#####
Bravo! I enjoyed the post, but let me clear up a few points.
In one of my early comments on the “Misunderstandings About The Pacific Decadal Oscillation” thread, I noted that I included the Newman et al paper because it was controversial. I, however, also included numerous graphs of the PDO compared to the SST anomalies of the North Pacific (North of 20N), compared to detrended SST anomalies of the North Pacific, etc. Here’s a link to my copy of the “Misunderstandings” post, with the larger illustrations for the far-sighted (like me):
http://bobtisdale.blogspot.com/2009/04/misunderstandings-about-pdo-revised.html
One illustration that many people missed was Figure 5, in which I subtracted global temperature anomalies from SST anomalies of the North Pacific, North of 20N (the area of the PDO), creating a “Residual” of sorts:
http://i42.tinypic.com/345kgsk.jpg
Note how the two datasets opposed one another from the 1940s to ~1976. During that period, the PDO was in the Cool Phase, and according to popular beliefs, the PDO should have been causing global temperatures to decline. Note, however, that the SST residuals were positive. This means that North Pacific SST anomalies were higher than Global temperature anomalies, and the North Pacific was actually contributing positive anomalies during that period. In other words, it was warming, not cooling. So that North Pacific SST anomalies actually opposed the global cooling during that period. They did not contribute or drive.
So why would global temperatures decline during that period? The Tropical Pacific SST anomalies are in “phase” with the PDO, as shown in my Figure 9 of that post:
http://i41.tinypic.com/n14010.jpg
And what dominates SST anomalies of the Tropical Pacific? ENSO.
Again, ENSO drives global temperature, not the PDO. It expresses the PATTERN of SST Variability of the North Pacific, nothing more.
Bill Illis (11:56:03) : “There is this great animation of clouds over one year which provides a real model of how the climate actually works. The Equator runs the climate and I don’t see a consistent Aleutian Low or an NPI in this animation.”
First, good links. I appreciate the info. The animation is helpful but is the issue of the Aleutian Low, as being discussed, not a multi-year phenomenon rather than something over the course of one year? The paragraphs after the three charts at the top seem to suggest so.
And in your statement I’ve quoted: “The Equator Runs the climate …”
Although I would substitute the “Intertropical Convergence Zone” (ITCZ) for Equator, I basically agree. The vertical Sun, and thus solar intensity, shifts over six months but sort of hangs at the solstices (“sun stands still’) while passing the Equator more rapidly. When over each Tropic, in turn, there is tremendous energy input in a 10 to 15 degrees of latitude band. There is more ocean area involved when the vertical sun is over the Tropic of Capricorn and there is a lag between energy input and the atmospheric movements. The areal extent of the combined ITCZ and the Trade Winds, and the oceans over which these processes occur, is much greater than for the other – extra tropical – lows and highs and so on. As an analogy, take a bucket of water out of a large swimming pool. Both will have the same temperature but the pool will have more heat (aka energy).
I also do not see much emphasis on the rotational aspect of Earth and the three dimensional shape of ocean basins applied to these problems. Recall the song “when you are spinning around, things come undone.”
Adam Gallon (11:06:42) : “Add in a contribution from our CO2 output and we’re nearly there?”
We don’t need no stinking “contribution from our CO2 output” – it is more or less miniscule and just clutters up the conversation.
Basil: You wrote, “Bob’s point was that ‘global warming’ cannot be attributed to the PDO. And depending on what one means by ‘global warming,’ he is no doubt correct. That is, if by ‘global warming’ we are speaking of the long rise in global temperatures since the earth came out of the ‘Little Ice Age,’ then certainly, the PDO cannot likely account for that.”
You missed my point. My point was the PDO reflects a pattern of SST variability in a specific part of the North Pacific. Nothing more. During positive phases of the PDO, SST anomalies in the extreme eastern North Pacific (North of 20N) tend to be positive, and the SST anomalies in the central and western North Pacific (North of 20N) tend to be negative. The reverse is true during the negative PDO phases.
Granted, the tendency of the SST anomalies in the eastern part of the North Pacific, being in phase with the PDO, will impact land surface temperatures in the Pacific Northwest. That is, a positive PDO would correlate with a tendency toward a positive LST anomaly in the Pacific Northwest. But the SST anomalies in the western part of the North Pacific also have an impact the land surface temperatures–in eastern Asia. Since the SST anomalies in that part of the North Pacific oppose the PDO, the impact is of the opposite sign.
You went on to illustrate the correlation between the PDO, NINO3.4 SST anomalies, and the inverted NPI.
Then you wrote, without showing cause and effect, “In other words, even if the PDO is not itself, over a complete cycle, contributing to ‘global warming,’ trends calculated this way will be biased upwards because of the transient impact of decadal and bidecadal influences of the PDO on global temperature.”
Basil, through what physical processes does the PDO, IN AND OF ITSELF, have transient impacts on global temperatures????
Bill Illis: The UCAR Cloud and Precipitation video from that model simulation was great. Thanks for the link. For those interested, the discussion page is here:
http://www.vets.ucar.edu/vg/CCM3T170/index.shtml
Bob,
I think you have accepted elsewhere that during a positive PDO the El Nino is enhanced and La Nina is suppressed. Vice versa during a negative PDO.
Can you indicate how you think the ENSO process might give rise to approximately 30 year phase shifts between positive and negative PDO phases ?
Mike Lorrey (10:52:26) – that comment is an excellent summation of the situation.
In reading this and Bob Tisdale’s previous post ( http://wattsupwiththat.com/2009/04/28/misunderstandings-about-the-pacific-decadal-oscillation/ ) — both very excellent discussions — this whole discussion of PDO & ENSO (and not to make light of it), I am reminded of mankind’s eternal conundrum — which came first, the chicken or the egg?
We can use statistics to discern patterns as we’ve seen above, but we seem to be at the stage of only discerning symptoms. We’ve still a long way to go. It’s no wonder then that politicians have grabbed hold of the CO2 cause – it’s so simple and easy to understand – no real thought is necessary – which, maybe, is why politicians did grab hold of it. (Shhh – be nice now.)
John F. Hultquist (09:14:20) :
Note: Under the three charts find Nino 3.1 and not 3.4
Power Spectrum: Nino 3.1, PDO, and NPI
The 3.1 is a typo; should be 3.4.
Northern Plains Reader (11:21:51) :
By Robert Livesay, do you mean “Livezey?” I’m aware of Livezey’s position on this. The question of whether the PDO can be reduced simply to red noise is addressed in Radionov (2006):
http://www.beringclimate.noaa.gov/regimes/Prewhitening2006GL025904.pdf
Bottom line quote:
Hence, it is unlikely that these regime shifts are
just manifestations of a red noise process. The red noise
component (Figure 4c), which is represented here by the
difference in the PDO series before and after the prewhitening,
accounts for about 25% of the total variance in PDO.
For those less familiar with the background here, there are some (like Livezey) who challenge the notion of “regime shift.” The “red noise” argument would reduce the PDO to a random walk. It would then become meaningless to speak of phases of the PDO, or shifts between one or the other being characteristic of the PDO for long periods at a time. It is, I think, a minority view, not one widely held.
On the paleoclimate record, McDonald & Case (2005):
http://www.sscnet.ucla.edu/geog/downloads/634/260.pdf
and a quote:
Second, the 50 to 70 year mode of PDO variability
inferred from instrumental observations of SST’s has been
generally persistent and significant over the past 200 years
and intermittently significant prior to that.
They do conclude that the paleo evidence is uncertain, and the mode unstable. A change in mode or phase is like pornography — we may not be able to predict it, but we know it when we see it.
Thanks to all. This is like sitting-in on a serious postt-grad seminar. Again, as an amateur, I look for the gorilla in the room: who has the big Joules here? The Sun of course, but then the ocean. And from there back into the air, thence to space. Stephen Wilde improves on the point I wanted to make. ..The other point I would make (not original with me) is geometry. As noted above by Illis (11:56:03) and Hultquist (14:56:16) the Equator (or equatorial region) is the big dog here. Imagine a map of the energy flux of sunlight onto surface area over time. It would be like that crazy homunculus from Psych 101, with a gigantic component from Lat 23 N to 23 S and a much lesser contribution from 23 to 67, and almost bupkis from there to the poles. So the power to drive the system, the engine room, is the tropics. And all this yammer about changing albedo at the poles just leaves me –cold.
Loving this conversation.
If there is a PDO teleconnection I would think it may involve mechanisms in the Indian Ocean and some sort of harmonic of the MJO.
Bill Illis, (11:56:03)
I just cannot get over the beauty of that animation.
It seems like Africa and the Amazon have a beating heart within them as the clouds change from white/blue to orange. In the Amazon basin the clouds are trapped against the Andes so they stay to make Brazil so productive.
The clouds regularly wash over the USA and Europe and then let the crops dry off for harvest.
In Australia the clouds seem to be avoiding the continent except for the last three months of the year, while New Zealand is regularly covered and revealed by bands of clouds.
With more observations, a meteorologist could see and understand so much more. I imagine how wonderful our understanding of the earth could be if the billions upon billions had been spent on observations like this. Can you imagine a database that contained animations of every part of earth science that has been studied? Can you imagine if these animations could be layered at the viewer’s whim and run forward or backward through a decade? Temperatures, winds, currents, sea ice, snow accumulations, clouds, tides and anything else that would aid understanding? Can you imagine looking to the earth for answers instead of to a computer projection?
When such a tool is available for twenty years or so perhaps it might be time to try to project the earth’s climate out to about three weeks and see how it goes. Until then let’s just look at the real numbers.
Thanks to Basil Copeland for a post that adds to our knowledge of the PDO. Two aspects in particular were helpful to me as someone interested in what happens in California and Japan: 1) The Aleutian Low and 2) Rossby Waves. Bob Tisdale’s article convinced me that the PDO is not a driver of anything, but an indicator (for me) of regime changes on a multidecadal basis in the Northern Pacific, which also seems to be an indicator of many other changes to global climate. It is an “index” that seems very important to pay attention to. Its discovery, as I undertand it, came from trying to find out what happened to salmon runs.
I am not able to understand a great deal of Dr. Copeland’s post, but I would be interested in feedback on the following. The first part connects Rossby Waves to ENSO.
Oceanic midlatitude Rossby Waves from my reading are mechanisms that carry El Nino signals to the opposite coast. “ENSO-induced perturbations in the tropics [can] propagate poleward along the ocean’s eastern boundaries as coastal trapped waves. These waves tend to evolve into Rossby waves and transmit the effects of ENSO into mid-latitude oceanic interiors.” (Siedler ea) There is another atmospheric Rossby wave from the Indo-Australian Convergence Zone that moves into the Central Pacific. A wave train is set off in the upper tropics, arcing poleward and eastward. This leads to enhancement and southward movement of the Aleutian Low.” (Oliver) Are either of these important for changes that lead to the PDO?
Steven Wilde: You wrote, “I think you have accepted elsewhere that during a positive PDO the El Nino is enhanced and La Nina is suppressed. Vice versa during a negative PDO.”
Actually, you wrote something to that effect in the “Misunderstandings About The Pacific Decadal Oscillation” thread. Refer to your 12:31:32 comment on 4/28. If I wrote it elsewhere, I don’t recall it. I’d like to illustrate the effect in a future post, though, if it’s there.
You asked, “Can you indicate how you think the ENSO process might give rise to approximately 30 year phase shifts between positive and negative PDO phases ?”
There’s lots of debate about what causes the phase shifts, as can well be seen, and as you’re aware, the phase shifts in the PDO and ENSO and NPI all appear to happen around the same time, as Basil illustrated above. Do they result from an atmospheric bridge from the North Atlantic? Do the shifts result from variability in the subsurface South Pacific as suggested by Bratcher and Giese? Does the Southern Ocean play a role?
I am interested in discussing the pros and cons of the negative PDO causing loopyness in the jet stream that affects weather around the globe as the jet stream circles the NH in its northern track. The reverse is also of interest. With the jet stream in its more southerly track with a positive PDO, the loopyness disappears and the jet stream is in a more linear track around the globe with fewer breaks and weather extremes. This may have more to do with the strength of the trade winds, which affects PDO, which affects the jet stream.
Bill Illis (11:56:03) :
Next one has to describe a physical reason for the NPI to be a driver of the PDO.
There is this great animation of clouds over one year which provides a real model of how the climate actually works. The Equator runs the climate and I don’t see a consistent Aleutian Low or an NPI in this animation.
https://www.ucar.edu/publications/nsf_review/animations/ccm3.512×256.mpg
We need to revisit some basic climatology here. [In this, I’m somewhat touching on what John F. Hultquist (14:56:16) : posted about the ICTZ; there is more to climate than the ITCZ.] The equator does not run the climate entirely. There are other climate forces beyond Hadley cells. In this discussion, the presence and positions of the northern continents and the polar cells lead to permanent lows and highs — the Aleutian and Icelandic lows, and the Siberian high. If those are not shown in your animation, then your animation is not a realistic depiction of global climate. So a physical reason for the NPI to drive the PDO — in part — exists. Though it is probably a misnomer to say the NPI is “driving” the PDO. They are just two representations of the same underlying physical subsystems.
For a physical mechanism, it is already there in Miller et al. For another explanation, here is Zhang and Delworth (2007):
The PDO consists of both the projection of ENSO
onto the North Pacific as well as North Pacific variability
that is independent from ENSO[emphasis supplied.]
In this paper, we focus on the latter part.
….
The modeling results suggest that the
AMO can contribute to the component of the PDO that is
linearly independent of ENSO, i.e. the NPMO, and the
associated PNA pattern.
[9] How does the North Atlantic-North Pacific teleconnection
occur and what affects the time lag between the PDO
and the AMO? Here we propose a mechanism (Figure 3) for
the influence of the AMO on the North Pacific multidecadal
variability:
[10] 1. During the positive (negative) AMO phase, the
warm (cold) North Atlantic SST anomaly leads to reduced
(enhanced) surface DJF northward atmospheric eddy heat
transport and upper level DJF eddy vorticity flux over both
the North Atlantic and the North Pacific mid-latitudes
(Supplementary Figure 6), in response to the enhanced
northward oceanic heat transport. This weakening (strengthening)
of the mid-latitude winter storm track results in a
poleward (equatorward) shift of the westerly wind, and thus
the weakening (strengthening) of the Aleutian Low, i.e. high
(low) SLP anomaly and positive (negative) PNA pattern
over the North Pacific.
[11] 2. The negative (positive) wind stress curl anomaly
associated with the high (low) SLP anomaly over the North
Pacific leads to an anomalous anticyclonic (cyclonic) midlatitude
gyre circulation (Supplementary Figure 7), and thus
a northward (southward) shift of the Kuroshio Current and
warm (cold) SST anomaly in the central and western North
Pacific, especially near the Kuroshio/Oyashio Extension
(KOE) region.
…..
[12] 3. The atmospheric response to the warm (cold) SST
anomaly in the KOE region leads to even stronger weakening
(strengthening) of the Aleutian Low, i.e. amplified
high (low) SLP anomaly and positive (negative) PNA
pattern over the North Pacific. Hence the North Pacific
air-sea interaction provides a positive feedback and the
excited North Pacific multidecadal mode can persist.
Source: http://www.gfdl.noaa.gov/bibliography/related_files/roz0704.pdf
Let me pick up and address Bob here:
Bob Tisdale (15:24:27) :
Then you wrote, without showing cause and effect, “In other words, even if the PDO is not itself, over a complete cycle, contributing to ‘global warming,’ trends calculated this way will be biased upwards because of the transient impact of decadal and bidecadal influences of the PDO on global temperature.”
Basil, through what physical processes does the PDO, IN AND OF ITSELF, have transient impacts on global temperatures????
and
Bob Tisdale (13:59:24) :
And what dominates SST anomalies of the Tropical Pacific? ENSO.
Again, ENSO drives global temperature, not the PDO. It expresses the PATTERN of SST Variability of the North Pacific, nothing more.
I wouldn’t disagree with the PDO being a “pattern” of variability, of something. I do disagree that it is all ENSO. Whatever the PDO is picking up, it is more than just a pattern of SST variability caused entirely by ENSO. If that’s your point, then we’ll have to agree to disagree. As to whether it is just SST, it is actually as much SLP as SST (which are just two sides of a coin). But again, the issue is not what it is as much as what causes it, and whether ENSO can explain the multidecadal periodicity of the PDO. There is no agreement that ENSO can explain the intradecadal variability, and maybe even decadal variability. But there is something more. Please, read Miller et al., and Zhang and Delworth. Don’t put all your PDO eggs in one basket (ENSO). 🙂
Incidentally, while I will be the last person to fail to express appreciation for the role of oceanic processes on global climate, of the energy received in the tropics, and redistributed over the globe, 50% more is redistributed by atmospheric circulation than by oceanic currents. So we need to broaden our horizons here, and not focus strictly on SST’s. Secular patterns in atmospheric circulation, oscillating between periods when zonal circulation dominates, and periods when meridional circulation dominates, have a lot to do with natural climate variability also. It is just not all about ENSO.
-Basil
I agree Basil. It isn’t all about SST’s. But I think the jet stream behavior is mostly influenced by what the oceans are doing. Once it hits land masses, it develops a life of its own. But I think that life can be characterized and modeled. If I had the computer chops to do it, I would be measuring jet stream behavior (literally, physical measurements of loops and digs (or lack thereof) along with pressure gradients and weather fronts) compared to PDO characteristics over several decades and see what we get in terms of temperature trends in the NH. Then I would do the same examination of the jet stream that surrounds the South Pole.
Bill Illis (11:56:03) :
I wonder why you have never done a guest post here?
Just Want Truth… (18:57:35) :
Bill Illis (11:56:03) :
I think I better clarify : It seems I learn as much or more from your comments than some of the posts here. So I am wondering why you haven’t had an interesting guest post?
Interesting thought from John Christy :
“There are some of us who remain so humbled by the task of measuring and understanding the extraordinarily complex climate system that we are skeptical of our ability to know what it is doing and why. As we build climate data sets from scratch and look into the guts of the climate system, however, we don’t find the alarmist theory matching observations.”
-John Christy
Director, Earth System Science Center at the University of Alabama (UAH)
Fascinating. Thanks. And the comments are wonderfully informative.
The jet stream has been loopy of late and WA is getting daytime temps 10 to 15 degrees cooler than “normal”, but the nights are about “normal.” Snow on the passes again today and tonight.
How much data does it take to be meaningful? It just seems to me that a couple hundred years of data is simply not enough observations to document the complete cycle. Yep, the sun looks to be in a minima, that helps. The glacial cycle seems to be more in the 25,000 to 50,000 year range. Is there a role for geomagnetism, and have we only observed it in a declining state? What other cycles are there?
I don’t mean to belittle any work done to date, but rather merely ask what is the likelihood that we have enough data to make comprehensive predictions or attribute causes and depict relationships with a high degree of certitude.
I’m only going for the lifetime of a tax cap and trade scheme based on a poorly thought-out and studied cause and affect relationship. I will leave the next hundred years to someone else. There is enough data for the next 30 years. After that, I will be in my doddering and drooling on my bib.
Pamela Gray (18:50:19) :
I agree Basil. It isn’t all about SST’s. But I think the jet stream behavior is mostly influenced by what the oceans are doing. Once it hits land masses, it develops a life of its own.
Pamela,
Earlier you mentioned the “loopiness” of the jet stream when the PDO is negative. I’m just a curious observer — I switched from physical geology/geology/geophysics to economics (environmental/resource economics) many years ago, so my climatology is rusty…but wouldn’t this be explained by the relative strength or weakness of the Aleutian Low? At least in North America.
The loopiness gives rise to (or is an expression of) times when winds are more meridional than zonal. There seem to be long epochs in which one or the other dominate. But why?
Any thoughts?
Basil
For some reason this all reminds me of a bunch of folks analyzing a violin.
One says “Look! The bridge modulates the body!”
Another says “But the area near the chin piece starts vibrating after the main body, the main body is the important driver.”
Yet a third says it’s the air in the body that drives the vibration and a fourth assures us all that the strings are where the energy comes from for all the rest and the air is just too thin…
And I’m just left wondering: What about the bow, and where is the musician that moves it…
Yes, complex systems can “ring” for a long time; but somewhere and at some time there is a modulating, driving, energy input that sets the whole thing ringing…
http://www.lavoisier.com.au/articles/greenhouse-science/solar-cycles/IanwilsonForum2008.pdf
So my take on it all is that we have this giant instrument, with resonant frequencies from 90 to 30 to 10 to ?? years based on small changes and with some resonances at 100,000 year intervals based on orbital mechanics (and potentially mid length cycles such as the 1500 year cycle); and we are surprised that the “sound” it makes in air pressures and movements is rich, deep, resonant and complex.
I’m reminded of the way a cymbal does the crash and ring with deep rich frequencies, some measured in whole seconds, others in milliseconds. They must be made just a bit non-symmetrical and with a non-smooth finish to get that effect. Our planet is very non-smooth and non-symmetrical leading me to expect many non-linear, complex and rich oscillations.
But where is the drumstick and the drummer?
If not orbital mechanics and not the sun, then what and where? The earths tilt? The daily spin? Precession and wobble? Can we reasonably expect to identify it from hearing the cymbal crash? Or hearing the brush slowly dragged across it?
One is left to wonder…
Basil: Regarding your 18:34:50 comment, I have no doubt that the PDO is a response to coupled Ocean-Atmosphere processes, just like ENSO is a response to coupled Ocean-Atmosphere processes. And I thank you for pointing to the NPI as an indicator of the atmospheric variability.
You wrote, “…of the energy received in the tropics, and redistributed over the globe, 50% more is redistributed by atmospheric circulation than by oceanic currents.”
Please explain where the 50% came from.