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Temporal structure of ENSO in 20 th Century Climate simulations

Temporal structure of ENSO in 20 th Century Climate simulations. Antonietta Capotondi NOAA/Earth System Research Laboratory Collaborators : Andrew Wittenberg, Simona Masina , Clara Deser , Mike Alexander, Yuko Okumura. Observations. CCSM3 (NCAR). GFDL . NASA GISS .

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Temporal structure of ENSO in 20 th Century Climate simulations

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  1. Temporal structure of ENSO in 20th Century Climate simulations AntoniettaCapotondi NOAA/Earth System Research Laboratory Collaborators: Andrew Wittenberg, SimonaMasina, Clara Deser, Mike Alexander, Yuko Okumura

  2. Observations CCSM3 (NCAR) GFDL NASA GISS ENSO in coupled climate models 2Evolution of the Niño3.4 index

  3. Spectral characteristicsNino3.4 index (5°S-5°N, 170°W-120°W) Capotondi, Wittenberg and Masina 2006

  4. What determines the ENSO timescale? • Guilyardi et al. (2004) have shown that atmospheric model resolution can be important. Higher atmospheric resolution leads to more realistic (longer) periods. • Fedorov and Philander (2001) have emphasized the importance of the mean state (intensity of the winds, depth and strength of the equatorial thermocline) as a controlling factor for ENSO properties. • Dewitte et al. (2007) have stressed the importance of thermocline depth. A shallow thermocline in the central-west Pacific may favor fast equatorial modes, and lead to a shorter timescale. • Simple oscillator models: Delayed oscillator, Recharge oscillator, Western Pacific oscillator, Advective-Reflective oscillator. Unified theory provided by Wang (2001).

  5. What determines the ENSO timescale?Studies based on intermediate coupled models emphasize the importance of the spatial structure of the anomalous wind stress Kirtman (1997) used an intermediate complexity model and surface wind stresses of different meridional scales.

  6. What determines the ENSO timescale?Studies based on intermediate coupled models An and Wang (2000) examined the causes for the longer ENSO period after the 1976-77 climate regime shift, and examined the changes in the pattern of the wind stress. Important aspects of anomalous wind stress pattern: Meridional width: increases adjustment time through extra-equatorial Rossby waves Longitudinal position: Controls whether anomalous advection of zonal mean temperature gradients promotes ENSO growth or phase transition.

  7. ‘Center of mass’ of τx 168°W Regression of τx upon the Niño3.4 indexNCEP/NCAR Reanalyses

  8. Regression of τx upon the Niño3.4 index NCEP CCSM3 GFDL-CM2.0 IPSL-CM4

  9. Regression of τx upon the Niño3.4 index GISS-EH PCM MRI

  10. Regression of τx upon the Niño3.4 index UKMO-HadCM3 CSIRO CNRM

  11. T vs. Ly T vs. C T vs. Tp(Ly,C) Dependency of period upon structure of anomalous wind stress

  12. CCSM3 vs. HadCM3

  13. Influence of meridional width ofτxRegression of the curl(τ) upon the Nino3.4 index

  14. Curl(τ) vs. Standard Deviation of pycnocline transportMeridional transport between the base of the mixed layer and the 26σθ isopycnal, zonally averaged from the eastern edge of the WBC and the eastern ocean boundary POP simulation forced with COARE climatology

  15. Meinen and McPhaden 2000 EOF1 EOF2 INGV ocean analysis Thermocline VariabilityDepth of 15°C isotherm (Z15)

  16. Influence of meridional width of τxEOF2 of thermocline depth INGV 10°N 10°S CCSM3 HadCM3

  17. Phase relationship between the Z15 modes PC2-PC1 lag-correlation INGV CCSM3 UKMO-HadCM3

  18. CCSM4 Observations HadISST Niño3.4 time series

  19. CCSM4- Spectra

  20. CCSM4: Wind Stress and Curl(τ) CCSM4

  21. CCSM4: Thermocline variability INGV CCSM4

  22. Seasonal Footprinting mechanism: CCSM4 vs. obs

  23. Seasonal Footprinting mechanism: CCSM3 vs. obs

  24. Asymmetry in the duration of El Niño and La Niña (Okumura and Deser 2010) HadISST 1900-1947 HadISST/NCEP 1948-2008 CCSM4 Dec+1 El Niño Dec0 Dec+1 La Niña Dec0

  25. Open Questions • Relative importance of wind forcing vs. mean upper-ocean stratification in determining the ENSO timescale • SST variations appear strongly correlated with thermocline variability in the CMIP3 models. What about S-modes? • Can models reproduce the SFM? SFM is a precursor of a large fraction of ENSO events. What is its connection with the Western Wind Events (WWE)? • Is the difference in duration of El Niño and La Niña events an important metrics to include in evaluating models? • Can the models reproduce the observed ENSO diversity, including amplitude and frequency modulation, and longitudinal position of the warming? What are the mechanisms?

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