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Axel Timmermann

Beyond the “simple” recharge paradigm. Axel Timmermann. Is ENSO still interesting?. Citations per year Source: Web of Science. title. abstract. Recap: ENSO recharge paradigm. Recap: ENSO recharge paradigm. Discharging, Sverdrup Transport term. + Damping nonlinearity.

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Axel Timmermann

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  1. Beyond the “simple” recharge paradigm Axel Timmermann

  2. Is ENSO still interesting? Citations per year Source: Web of Science title abstract

  3. Recap: ENSO recharge paradigm

  4. Recap: ENSO recharge paradigm Discharging, Sverdrup Transport term + Damping nonlinearity

  5. Beyond the “simple” recharge paradigm • Nonlinearity, skewness and bursting • Annual-cycle ENSO coupling • Noise-induced instability • ENSO flavors • ENSO “diversity” • Response to external forcing

  6. Reasons for ENSO skewness Saddle node 1. Nonlinear SST equation • 2. Nonlinear atmospheric response • convection depends on total SST • Interaction of ENSO with atmospheric noise

  7. ENSO skewness and ENSO bursting

  8. ENSO skewness and ENSO bursting • Radiative conv. • Equilibrium state is • saddle point • Highly unstable Period-doubling Bifurcations generate Chaos and low-frequency Variability There is a permanent La Nina state for large coupling

  9. ENSO skewness and ENSO bursting Error growth rate strongly state- dependent Certain stretches on attractor of well Predictable Possibility for regime predictability

  10. Nonlinear Atmospheric Response S. Philip 2009 Wind response to quadratic SSTA • For a large El Nino, the warm pool and main convection center extend eastward, • enhanced westerly wind anomalies • For a large La Nina, the main convection zone shrinks • Weaker easterly wind response With atmospheric nonlinearity And state-dependent noise

  11. Beyond the “simple” recharge paradigm • Nonlinearity, skewness and bursting • Annual-cycle ENSO coupling • Noise-induced instability • ENSO flavors • ENSO “diversity” • Response to external forcing

  12. ENSO annual cycle interaction Annual cycle ENSO PDO, IPO MJO, WWB

  13. Periodically modulated coupling of a linear oscillator Observations γ(t) =γ0+α sin(ωat) Recharge model Amplitude Modulation

  14. Periodically forced NONLINEAR OSCILLATOR produces…. K Ω Arnol’d Tongues

  15. Periodically forced NONLINEAR OSCILLATOR produces the Devil’s Staircase

  16. Periodically forced NONLINEAR OSCILLATOR produces the Devil’s Staircase

  17. Periodically forced NONLINEAR OSCILLATOR produces frequency entrainment Effect of AMOC Shutdown on ENSO Stroboscopic view ENSO amplitude Dominant frequency Annual cycle amplitude

  18. Orbital forcing effects on ENSO Abrupt changes of ENSO 140,000-100,000 years ago 140,000-100,000 years ago Abrupt changes of ENSO Timmermann et al. (2007)

  19. Beyond the “simple” recharge paradigm • Nonlinearity, skewness and bursting • Annual-cycle ENSO coupling • Noise-induced instability • ENSO flavors • ENSO “diversity” • Response to external forcing

  20. Noise-induced intensification of ENSO Eisenman et al. 2005 WWB modulation by temperature for present-day climate

  21. ENSO recharge model with state-dependent noise Coupling strength and noise may change slowly over time

  22. ENSO recharge model with state-dependent noise Ensemble mean equation for ENSO State-dependent noise is “coupling” State-dependent noise is also “nonlinearity”

  23. ENSO recharge model with state-dependent noise Coupling strength and noise may change slowly over time

  24. ENSO recharge model with state-dependent noise Ensemble mean equation for ENSO State-dependent noise is “coupling” State-dependent noise is also “nonlinearity”

  25. ENSO recharge model with state-dependent noise Ensemble variance equation for ENSO Deriving third order equations and 4th Order closure We can obtain a closed set of equations for the ensemble variance

  26. ENSO recharge model with state-dependent noise period Teast period/2 Temperature variance Time [months] Instability of the second order moments is associated with error dynamics

  27. Beyond the “simple” recharge paradigm • Nonlinearity, skewness and bursting • Annual-cycle ENSO coupling • Noise-induced instability • ENSO flavors • ENSO “diversity” • Response to external forcing

  28. Multiplicity of ENSO modes Westward-propagating SST mode Interannual mode Quasi-biennial mode Warm-pool El Nino, Modoki

  29. The SST mode Simplified Gill solution

  30. The SST mode equation A westward propagating SST mode! Note the zonal T derivative originates From the wind stress, not directly from The zonal advection.

  31. The Thermocline mode Ignore ocean current anomalies Simplified Gill solution: K-wave Reduced gravity equations

  32. The Mixed-Thermocline mode The mixed mode

  33. Cold tongue versus warm pool El Nino EOF2, Timmermann 2001 EOF2, Timmermann 2003 Dateline El Nino, Larkin and Harrison 2005 El Nino Modoki, Ashok et al. 2007 Central Pacific El Nino, Kao and Yu 2009 Warm Pool El Nino, Kug et al. 2009 SST and precipitation

  34. El Nino flavors and their impact on Australia EOF2 of SSTA, Timmermann et al. 2003 Cold tongue El Nino Modoki drought DJF MAM JJA SON Courtesy of Harry Hendon

  35. El Nino flavors and their impact on Australia EOF2 of SSTA, Timmermann et al. 2003 Modoki Explains why the rainfall response to the El Nino 1997/98 was relatively weak in Australia drought DJF MAM JJA SON Courtesy of Harry Hendon

  36. Beyond the “simple” recharge paradigm • Nonlinearity, skewness and bursting • Annual-cycle ENSO coupling • Noise-induced instability • ENSO flavors • ENSO complexity • Response to external forcing

  37. ENSO complexity From Slingo

  38. What controls the amplitude of ENSO? Noise level dT/dt=f (T,u..)+Σ(T)ζ ENSO variance maybe skewness Strength of annual cycle dT/dt=f (T,u..)+Asinωt Nonlinearities dT/dt=f (u'T', Σ(T)ζ) Background state dT/dt=f (T,u,h,v,w) External factors

  39. Beyond the “simple” recharge paradigm • Nonlinearity, skewness and bursting • Annual-cycle ENSO coupling • Noise-induced instability • ENSO flavors • ENSO “diversity” • Response to external forcing

  40. Projected climate change versus model bias Many state-of-the-art coupled general circulation models still suffer from biases in the mean and the annual cycle Enhanced equatorial warming pattern, dominant climate response in the tropical Pacific +2C -2C 2-4C SST model bias SST model bias in a “typical” state-of-the-art climate model

  41. ENSO performance in climate models Standard deviation of sea surface Temperature anomalies Guilyardi et al. 2009

  42. Future Changes of ENSO, AR4 “All IPCC AR4 models show continued ENSO interannual variability in the future no matter what the change in average background conditions, but changes in ENSO interannual variability differ from model to model.” , IPCC AR4 ENSO change 2100 Yamaguchi and Noda

  43. Noise-induced intensification of ENSO AR4 models simulate increased Intraseasonal variability WWB-ENSO interaction increased during the last 50 years

  44. Conclusions TODAY IN THE FUTURE

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