Whither ENSO

1990 control (300yr), 2xCO2 (600yr), 4xCO2 (600yr)
Delworth et al., Wittenberg et al., Merryfield et al., Joseph & Nigam (JC 2006), Wittenberg (GRL 2009) Zhang et al. (MWR 2007); van Oldenborgh et al. (OS 2005); Guilyardi (CD 2006); Reichler & Kim (BAMS 2008) Kug et al. (JC 2010), Vecchi & Wittenberg (WIREsCC 2010), Collins et al. (Nature Geosci. 2010)
Best hope for long-term ENSO predictability?
NINO3 memory might last 5yr, following strong warm events.
Given enough years, we can say...
CM2.1 ENSO is too strong
These are what perfect forecasts look like!
(perfect model, near-perfect initial conditions, 40 members)
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“Perfect” ensemble reforecasts
Summarize the ensemble PDF with quartiles.
25th and 75th percentiles of NINO3 SSTA, from 40 members
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“Perfect” ensemble reforecasts
Quartiles “forget” initialization after a few years.
gray: 95%-bands for control quartiles, from 5000 resampled 40-ensembles
Both historical & paleo records suggest past modulation of ENSO
Historical SSTA (ERSST.v3)
Palmyra corals (Cobb et al., Nature 2003)
Multiproxy reconstructions: e.g. Emile-Geay et al. (2011abc, subm.)
Whither ENSO?
Assessing El Niño/Southern Oscillation risks for the coming decades
Andrew Wittenberg NOAA/GFDL
Earth's dominant year-to-year climate fluctuation:
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“Perfect” ensemble reforecasts
Other members look nothing like the control.
(forecasts with maximum NINO3 SST RMS error over each decade)
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“Perfect” ensemble reforecasts
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Decadal statistics of ENSO
Ensemble forecasts of ENSO activity
smoothed NINO3 SSTA amplitude from 40 members
பைடு நூலகம்
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Decadal statistics of ENSO
Activity distributions also “forget” the ICs
{10,50,90}-percentiles of smoothed amplitude, with 95%-bands from control
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Long-term memory?
Distribution of inter-event wait times suggests that NINO3 SSTA might have some memory beyond 5 years.
5-year wait most common
3822yr / 495 events = 7.7yr mean wait
consistent with Poisson
ENSO events and their nearest neighbors
strong events more isolated
Meehl et al. (IPCC-AR4 2007) Guilyardi et al. (BAMS 2009) Vecchi & Wittenberg (WIREs CC 2010) Collins et al. (Nature Geosci. 2010)
correl(SST trend of 1%/yr, SST.PC1 of PICTRL) 10S-10N, 120E-80W Yamaguchi & Noda (JMSJ 2006)
What sort of ENSO do we simulate?
strong, skewed, long period, eastward propagating (1980s & late 1990s) weak, biennial, “Modoki” (early 1990s & 2000s)
Wittenberg (GRL 2009)
Modulation of NINO3 SST power spectrum
(e.g. satellites, TAO) (e.g. reconst SST)
2000yr mean
Wittenberg (GRL 2009)
Centuries of weak or strong ENSOs
CM2.1 ENSO is very sensitive to some parameters
Pre-industrial range of 100yr spectra
Vecchi & Wittenberg (WIREsCC 2010)
Projected ENSO changes (CMIP3/AR4)
Weak/ambiguous near-term anthropogenic impacts on ENSO Intrinsic modulation
Reviews:
Absolute value of NINO3 SSTA (degC)
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Decadal statistics of ENSO
Smoothed measure of ENSO activity
NINO3 SSTA amplitude, smoothed with 4yr running mean
Normal
El Niño
NOAA/CPC
How will ENSO behave in the coming decades?
ENSO drives/confounds global SI-to-decadal variability. CMIP5 & AR5 – new focus on near-term (30yr) projections. If we knew the next decade would have: - mega-ENSO → insure, invest, prepare, monitor & model - no ENSO → different investments, e.g. rebuild habitats
regular & westward propagating (1960s & 70s)
These are from a single run with unchanging forcings.
20 centuries of simulated NINO3 SSTs
annual means & 20yr low-pass
CM2.1 mean state hardly differs between active/inactive ENSO centuries
How predictable are decades of extreme ENSO?
Will Will Willforecasts forecasts forecast Will Will forecasts forecasts ensembles capture capture Tinycapture perturbation: the events, track differ intensity anything the if between control? notof their at the all? epochs? timing? epoch?
+0.0001C at one gridcell (equator, 180W, top 10m)
NINO3 SSTA
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“Perfect” ensemble reforecasts
Some members resemble the control.
(forecasts with minimum NINO3 SST RMS error over each decade)