S2 03 Tony Barnston IRI

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A review of 2005/2006 ENSO Predictions Tony Barnston Lisa Goddard Shuhua Li International Research Institute for Climate and Society (IRI)

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* * * * * * * * *La Nina, Dec-Mar ’05-06 *El Nino, October ‘06 Two Events of Interest: A brief La Nina(*), and a 'new' El Nino (*)

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-------------------------------------------------------------------- | | | | | | | | | | | Last week’s SST anomaly

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Renewed, east-extended westerly wind anomalies

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mid-Oct ‘06

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** *

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Climate Prediction Center NCEP * *

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From Climate Diagnostics Center, Boulder, Colorado * * Black: This year

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The onset of La Nina conditions in December 2005, after a largely ENSO-neutral northern autumn, was unprecedented since 1950. How did it emerge?

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H H ← ← ← Sep 2005 L ← ← ← e q u a t o r------------ Colombia Peru 110W Precursor to Brief La Nina Conditions in late 2005 Note: Vern Kousky says this anticyclone is spurious, due to Reanalysis biases.

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← ← ← H H H Oct 2005 e q u a t o r------------ Colombia Peru 110W Precursor to Brief La Nina Conditions in late 2005 Note: Vern Kousky says this anticyclone is spurious, due to Reanalysis biases.

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Nov 2005 H H H ← L H e q u a t o r------------ Colombia Peru 110W Precursor to Brief La Nina Conditions in late 2005 Note: Vern Kousky says this anticyclone is spurious, due to Reanalysis biases.

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Five-Day Zonal Wind, SST, and 20º Isotherm Depth Anomalies along Equator Zonal Wind SST 20º Isotherm Depth Mid-2005 to Mid-2006: Brief La Nina Conditions * *

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How did statistical and dynamical ENSO prediction models fare regarding the brief 2005-06 La Nina conditions and the late 2006 El Nino development?

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Cool Conditions Coming

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Cool Conditions Coming

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Cool Conditions Coming

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El Nino Conditions Coming

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El Nino Conditions Coming

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El Nino Conditions Coming

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----------------------------------------------------------------------------- .

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----------------------------------------------------------------------------- . Unanticipated by stat models

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--------------------------------------------------------------- --------------------------------------------------------------- . . Unanticipated by stat models

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. * Hybrid Models: Dynamical ocean, statistical atmosphere Blue asterisk * means the model did comparatively well during this period.

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. Abbreviated dynamical coupled models Blue asterisk * means the model did comparatively well during this period.

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. * * Fully comprehensive coupled models: Run in the U.S. Blue asterisk * means the model did comparatively well during this period.

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. * * * Fully comprehensive coupled models: Run outside of U.S. Blue asterisk * means the model did comparatively well during this period.

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. * Statistical models based on the redness of the coupled system Blue asterisk * means the model did comparatively well during this period.

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. * Statistical models based on linear or nonlinear regression Blue asterisk * means the model did comparatively well during this period.

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. * * Statistical models based on unique designs (regression to construct an analog, neurological network). Blue asterisk * means the model did comparatively well during this period.

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The following graphs show how each model did in predicting the ENSO state from JFM 2006 to ASO 2007, by one-month increments (so there are up to 18 3-month periods), for lead times of 1 to 5 months (1 month lead is really 'zero lead', such as a forecast for JFM made from December [or even earlier] initial conditions). Scores: Correlation (uncentered; means not removed) RMSE Skill score: ( 1 – [RMSEmodel/RMSEclim] ) The blue curve shows the model skill. The pink curve shows the skill of persistence from the most recently observed one month SST.

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(blue line) persistence

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* * (blue line) persistence

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(blue line) persistence

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(blue line) persistence

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(blue line) persistence

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* * (blue line) persistence

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* * (blue line) persistence

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(blue line) persistence

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* (blue line) persistence

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* * (blue line) persistence

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* * (blue line) persistence

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(blue line) persistence

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(blue line) persistence

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* * (blue line) persistence

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(blue line) persistence

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(blue line) persistence

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(blue line) persistence

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* * (blue line) persistence

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* * (blue line) persistence

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* * (blue line) persistence

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(blue line) persistence

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(blue line) persistence

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(blue line) persistence

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CPC, early November: …current conditions stronger-than-average easterly winds over the central equatorial Pacific) and recent observed trends (decreas-ing SST anomalies throughout the central and eastern equatorial Pacific) do not support the development of El Niño. Rather, they support either a continuation of ENSO-neutral conditions or the development of weak La Niña conditions during the next 6-9 months. CPC, early October: ….current conditions and recent observed trends support a cont-inuation of ENSO-neutral cond-itions for the next 3-6 months. IRI, mid-October: The likeli-hood of maintaining neutral conditions is at least 95% through the end of 2005. The probability of a La Niña dev-eloping between now and the end of 2005 is approxi-mately 1%. IRI, mid-November: The likeli-hood of maintaining neutral conditions is virtually certain through the end of 2005. The probability of a La Niña devel-oping between now and the end of 2005 is less than 1%. End of 2005: CPC and IRI statements about La Niña

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CPC, early December: …current conditions (stronger-than-average easterly winds over the central equatorial Pacific) and recent observed trends (decreasing SST anomalies throughout the central and eastern equatorial Pacific) do not support the development of El Niño. Rather, they support either a continuation of ENSO-neutral conditions or the development of weak La Niña conditions. IRI, mid-December: …the probab-ility of a La Niña developing over the next season is approximately 10%, increasing to about 20% by mid-2006. The chances for developing El Niño conditions are estimated at less than 1% through March 2006, increasing to approx-imately 20% by mid-2006. The likelihood of maintaining neutral conditions remains very high through early 2006. End of 2005: CPC and IRI statements about La Niña

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Middle to Late 2006: CPC and IRI statements about El Niño CPC, early September: Synopsis: ENSO-neutral conditions are expected to continue for the next one to two months, with weak warm episode (El Niño) conditions likely by the end of 2006. CPC, early August: Synopsis: ENSO-neutral conditions are expected to continue for the next one to three months, with a 50% chance that weak El Niño conditions will develop by the end of 2006. IRI, mid-August: The likeli-hood of maintaining neutral conditions is at 60% through the end of 2006, and the probability of an El Niño dev-eloping between now and the end of 2006 is approxi-mately 35 to 40%. IRI, mid-September: The likeli-hood of maintaining neutral conditions through the end of 2006 is about 40%. The probability of an El Niño devel-oping between now and the end of 2005 is approximately 60%. Likely El Niño strength would be weak.

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CPC, early October: Synopsis: El Niño coniditions are likely to continue into early 2007. Collectively, [these] conditions are consistent with the early stages of El Niño in the tropical Pacific. IRI, mid-October: …the probab-ility of continuing El Niño condi-tions over the next season is approximately 80%. The likelihood of neutral conditions is just under 20%. Likely strength of El Niño is weak to moderate. Middle to Late 2006: CPC and IRI statements about El Niño CPC did slightly better, on average, with these two somewhat unusual ENSO developments than IRI. But CPC usually does not usually quantify its ENSO forecasts probabilistically.

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Conclusion In the middle of the 2000-2009 decade, we still have weak to fair skill in predicting the onset of non-neutral ENSO conditions during the early half the calendar year. In 'new' situations (e.g. Dec. 2005, or autumn 2006), we receive surprises even at times of the year when we thought we had high confidence. Often, we predict non-neutral ENSO developments once we observe signs of the emergence of an event in the middle part of the calendar year. Sub-surface sea temperature anomalies may sometimes precede SST anomalies by a month or more. Once an event begins, we are skillful at predicting its evolution and are helpful to users whose season of climate effects is later. If climate change is causing different relative relationships with- in the new normal ranges, then statistical models may fail us. We are MUCH better than we were 20 years ago. To the layman, however, our ENSO predictive skill likely still looks weak to fair.