Walker circulation and ENSO

A paper well worth reading on the relationship between the Walker circulation and ENSO is Weakening of the Walker Circulation and apparent dominance of El Nino both reach record levels, but has ENSO really changed?, by Scott Power of the Australian Bureau of Meteorology, and Ian Smith of CSIRO. It is very well written and helpful. They aim to prove a notion:

We also document what appears to be a concurrent period of unprecedented El Nino dominance. However, our results, together with results from climate models forced with increasing greenhouse gas levels, suggest that the recent apparent dominance might instead reflect a shift to a lower mean SOI value.

The idea is that global warming is causing a weakening of the Walker circulation, and consequently more negative SOI values, on average. Dr Jones has proposed that this is the reason the cumulative sum of SOI is highly correlated with global temperatures. I think the data only show the ‘period of unprecedented El Nino dominance’ between 1976 and 1998 produces the trend, and cSOI largely matches all the wiggles in between.

Perhaps the difference is: a belief in a generalized weakening in the Walker circulation related to GW, vs a specific anomalous period of SOI generating a large part of global warming.

Power and Smith go on to make some other interesting statements. They note the disagreement about ENSO between models, and the relationship between weakening of the Walker circulation and the apparent intensity of the post 1977 period:

The Walker Circulation tends to weaken in climate models forced with increasing greenhouse gases [Tanaka et al., 2004; Vecchi et al., 2006; Meehl et al., 2007].

[18] On the other hand, there is currently no consensus amongst climate models concerning change in the behaviour of ENSO in response to global warming [Cane, 2005; Collins et al., 2005; Guilyardi, 2006; Nyenzi and Lefale, 2006; Philip and van Oldenborgh, 2006; van Oldenborgh et al., 2005; Zelle et al., 2005; Meehl et al., 2007].

[19] However, if global warming is largely responsible for the observed decline in the average value of the SOI over the period 1977 – 2006 then the threshold values used to define ENSO events need to be lowered (by approximately 3 SOI units). Under the new thresholds the apparent dominance of El Nino disappears.

This is similar situation whereby the frequency of extreme events, like heatwaves, appear to increase when the trend of average temperatures is increasing. Finally they say:

This simple interpretation gives a result that is consistent with modelling results:
global warming weakens the Walker Circulation and warms the tropical Pacific Ocean, but has little impact on tropical ENSO-driven variability about the new mean-state [Meehl et al., 2007]. While plausible, further research is needed to help quantify the extent to which global warming has in fact driven the unprecedented recent decline in the 30-year average value of the SOI. Southern Oscillation Index (SOI, blue).

However, they did not exclud the possibility that the apparent drift in Walker circulation is an artifact of the ‘period of unprecedented El Nino dominance’. They support the change in the baseline SOI with a structural break model, a methodology that luke claims is not used by real climate scientists and Nick says is ‘technical analysis’.

The break model is consistent with a ‘period of unprecedented El Nino dominance’, not only a weakening in the Walker circulation. To support their hypotheses they would need a significant negative slope on the SOI and other indexes prior to 1977, something that I bet isn’t there — a little fly in the ointment not disclosed by the authors.

It does not affect our study however, as the presence of a ‘drift down’ in the SOI mean would not affect the correlation of the cSOI, as linear regression adjusts the coefficient to compensate for this. This is one of the reasons its unreliable to estimate relative contributions from linear regressions.

Nor does it affect attempts to quantify the effects of the ‘period of unprecedented El Nino dominance’ on global mean temperature — an effect despite acknowledgment in the AR4 does not have been seriously considered as a contributor to the ‘unprecedented’ warming trend since 1960.

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0 thoughts on “Walker circulation and ENSO

  1. Southern Ocean SST anomalies impact the equatorial Pacific via the Humboldt Current. The following is a graph of Southern Ocean SST anomalies (ERSST.v3b version) for the areas south of the South Atlantic, South Pacific and Indian Oceans.

    It appears that all three of those datasets rise well before the 1976 start of the ‘period of unprecedented El Nino dominance’. Is there a 5 to 10 year lag between the upswing in Southern Ocean SST anomalies and the shift in ENSO from La Nina to El Nino dominance?

    The Southern Ocean SST anomalies south of the Atlantic and Indian Oceans when combined appear to have what could be a 100-year cycle.

    But the area south of the Pacific appears to receive a delayed and “smoothed” ENSO signal, which would feed back up to the equatorial. (And I’m not sure what to make of the two curious-looking spikes in the Pacific data prior to 1910.)

    I discussed those Southern Ocean datasets in this post:
    http://bobtisdale.blogspot.com/2009/04/closer-look-at-ersstv3b-southern-ocean.html

    Regards

      • Clarification: But I was suggesting that the multidecadal rise and fall in the Southern Ocean SST anomalies, which preceded the ‘period of unprecedented El Nino dominance’, were responsible for the extra strength of the significant El Nino events that began with the 1972/73 El Nino.

        A question that probably belongs on an earlier thread. Could the 1972/73 El Nino have been responsible for the Pacific Climate Shift of 1976? It was a significant El Nino with a two-year La Nina to “stabilize” things. That La Nina ended in 1976 (coincidentally) and was followed by two lesser (secondary?) El Nino events in 1976/77 and 1977/78. In 1974, Fuego (not too large with a DVI of 200) erupted, which would have added slightly to the impact of the La Ninas.

        The timing looks right.

        Regards

  2. Southern Ocean SST anomalies impact the equatorial Pacific via the Humboldt Current. The following is a graph of Southern Ocean SST anomalies (ERSST.v3b version) for the areas south of the South Atlantic, South Pacific and Indian Oceans. http://i39.tinypic.com/2qch20w.jpg It appears that all three of those datasets rise well before the 1976 start of the ‘period of unprecedented El Nino dominance’. Is there a 5 to 10 year lag between the upswing in Southern Ocean SST anomalies and the shift in ENSO from La Nina to El Nino dominance? The Southern Ocean SST anomalies south of the Atlantic and Indian Oceans when combined appear to have what could be a 100-year cycle. http://i41.tinypic.com/qsjwwp.jpgBut the area south of the Pacific appears to receive a delayed and “smoothed” ENSO signal, which would feed back up to the equatorial. (And I’m not sure what to make of the two curious-looking spikes in the Pacific data prior to 1910.) I discussed those Southern Ocean datasets in this post:http://bobtisdale.blogspot.com/2009/04/closer-l…Regards

  3. Ugh. Read that paper and there was some stuff of interest but a whole lot of nonsense.

    I mean, “since global warming has accelerated…”-the reference is to the SPM!!! What’s more, it is incredibly easy to see that this claim is one of those third kinds of lies-horrible, horrible statistics!!! Tell me, where is the bloody acceleration?

    AGH!!!

  4. Ugh. Read that paper and there was some stuff of interest but a whole lot of nonsense.I mean, “since global warming has accelerated…”-the reference is to the SPM!!! What's more, it is incredibly easy to see that this claim is one of those third kinds of lies-horrible, horrible statistics!!! Tell me, where is the bloody acceleration?http://i23.photobucket.com/albums/b370/gatemast…AGH!!!

  5. Clarification: But I was suggesting that the multidecadal rise and fall in the Southern Ocean SST anomalies, which preceded the ‘period of unprecedented El Nino dominance’, were responsible for the extra strength of the significant El Nino events that began with the 1972/73 El Nino.A question that probably belongs on an earlier thread. Could the 1972/73 El Nino have been responsible for the Pacific Climate Shift of 1976? It was a significant El Nino with a two-year La Nina to “stabilize” things. That La Nina ended in 1976 (coincidentally) and was followed by two lesser (secondary?) El Nino events in 1976/77 and 1977/78. In 1974, Fuego (not too large with a DVI of 200) erupted, which would have added slightly to the impact of the La Ninas. The timing looks right.Regards

    • Carl, Yes I saw it thanks, since you are on my Google Reader list, but
      I am happy for you to bring it to the attention of my readers. I
      particularly like:

      “You’d think that after $79 billion dollars of government-funded
      research just in the United States, someone would have bothered to
      detrend sea level data to discover that ENSO is radiative.”

      Do you think the issue of ENSO radiative vs non-radiative is major.
      Do you have references. I know that Douglass has just published on
      this.

      Cheers

  6. Carl, Yes I saw it thanks, since you are on my Google Reader list, butI am happy for you to bring it to the attention of my readers. Iparticularly like:”You’d think that after $79 billion dollars of government-fundedresearch just in the United States, someone would have bothered todetrend sea level data to discover that ENSO is radiative.”Do you think the issue of ENSO radiative vs non-radiative is major.Do you have references. I know that Douglass has just published onthis.Cheers

  7. Chicken or egg; solar or ENSO; I thought this was interesting and resolved the ‘which comes first’ issue;

    Carl Wolk (12:16:22) :

    Also note that the rises in temperature in 1976, 86/7, and 97/8 preceded the rises in solar activity

    Carl’s comment is from the Scafetta thread at WUWT and seems to suggest to this bemused mind that the ENSO starts the warming; but then this;

    “Stephen Wilde (12:21:26) :

    It is necessary to attribute sufficient modulating effects to the filtering of the TSI signal through the oceans.

    It is necessary to recognise that all the events in the air including cloudiness and albedo changes are a consequence of changes in the rate of energy emission from the oceans and not themselves a cause of climate change whether or not changes in cosmic ray quantities have some effect on overall cloudiness.

    The Svensmark theory might have a modulating effect on the primary effect on climate initiated by the oceans but does not in itself initiate anything. The absence of a 30/60 year periodicity in cosmic ray quantities is evidence of that. If Svensmark were right we would see an 11 year periodicity in oceanic phase changes but we do not.

    It needs to be appreciated that changes in the radiative balance of the oceans is a combination of long term solar changes and shorter term internal oceanic changes. Consequently very small changes in solar input can build up over several solar cycles (usually about 3) to enable a phase shift in the oceans to reveal that in the intervening period there has been a small background trend (the ’stepped’) effect.

    Whilst there is an upward solar background trend the steps will be slightly raised from the end of one positive phase to the beginning of the next positive phase at approximately 30 year intervals

    The opposite for a downward solar background trend.”

    I guess the main point is that CO2 climate sensitivity is being squeezed down to inconsequence.

  8. Chicken or egg; solar or ENSO; I thought this was interesting and resolved the 'which comes first' issue;Carl Wolk (12:16:22) : Also note that the rises in temperature in 1976, 86/7, and 97/8 preceded the rises in solar activityCarl's comment is from the Scafetta thread at WUWT and seems to suggest to this bemused mind that the ENSO starts the warming; but then this;”Stephen Wilde (12:21:26) : It is necessary to attribute sufficient modulating effects to the filtering of the TSI signal through the oceans.It is necessary to recognise that all the events in the air including cloudiness and albedo changes are a consequence of changes in the rate of energy emission from the oceans and not themselves a cause of climate change whether or not changes in cosmic ray quantities have some effect on overall cloudiness.The Svensmark theory might have a modulating effect on the primary effect on climate initiated by the oceans but does not in itself initiate anything. The absence of a 30/60 year periodicity in cosmic ray quantities is evidence of that. If Svensmark were right we would see an 11 year periodicity in oceanic phase changes but we do not.It needs to be appreciated that changes in the radiative balance of the oceans is a combination of long term solar changes and shorter term internal oceanic changes. Consequently very small changes in solar input can build up over several solar cycles (usually about 3) to enable a phase shift in the oceans to reveal that in the intervening period there has been a small background trend (the ’stepped’) effect. Whilst there is an upward solar background trend the steps will be slightly raised from the end of one positive phase to the beginning of the next positive phase at approximately 30 year intervals The opposite for a downward solar background trend.”I guess the main point is that CO2 climate sensitivity is being squeezed down to inconsequence.

  9. Chicken or egg; solar or ENSO; I thought this was interesting and resolved the 'which comes first' issue;Carl Wolk (12:16:22) : Also note that the rises in temperature in 1976, 86/7, and 97/8 preceded the rises in solar activityCarl's comment is from the Scafetta thread at WUWT and seems to suggest to this bemused mind that the ENSO starts the warming; but then this;”Stephen Wilde (12:21:26) : It is necessary to attribute sufficient modulating effects to the filtering of the TSI signal through the oceans.It is necessary to recognise that all the events in the air including cloudiness and albedo changes are a consequence of changes in the rate of energy emission from the oceans and not themselves a cause of climate change whether or not changes in cosmic ray quantities have some effect on overall cloudiness.The Svensmark theory might have a modulating effect on the primary effect on climate initiated by the oceans but does not in itself initiate anything. The absence of a 30/60 year periodicity in cosmic ray quantities is evidence of that. If Svensmark were right we would see an 11 year periodicity in oceanic phase changes but we do not.It needs to be appreciated that changes in the radiative balance of the oceans is a combination of long term solar changes and shorter term internal oceanic changes. Consequently very small changes in solar input can build up over several solar cycles (usually about 3) to enable a phase shift in the oceans to reveal that in the intervening period there has been a small background trend (the ’stepped’) effect. Whilst there is an upward solar background trend the steps will be slightly raised from the end of one positive phase to the beginning of the next positive phase at approximately 30 year intervals The opposite for a downward solar background trend.”I guess the main point is that CO2 climate sensitivity is being squeezed down to inconsequence.

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