1. ENSO-Basic State Interactions Jin-Yi Yu Department of Earth System Science University of California, Irvine

2. Monthly niño3.4 index (HadISST) NINO3.4 SST Index 1997/98 1982/83 1972/73

3. Monthly niño3.4 index (HadISST) NINO3.4 SST Index 1997/98 1982/83 1972/73

4. Monthly niño3.4 index (HadISST) Interval of decade(10-15yr) happens by chance? 1997/98 1982/83 1972/73

5. A Decadal Modulation of ENSO Intensity envelope function (square rooted) Nino3.4 (HadISST) Power Spectrum of the Envelope Function

6. HadISST (1870-2006) Mann et al. (1650-1980) ERSST.v.2 (1880-2006)

7. Composite ENSO SST Structures STRONG ENSO WEAK ENSO El Nino La Nina El Nino La Nina EPO CPO

8. + - - + + _ Warm El NiñoCold La Niña + _ Warm El NiñoCold La Niña basic state changesENSO forcing

9. ENSO-Basic State Interaction Mechanism El Nino Basic State 1 Strong ENSO Activity El Nino Basic State 2 Weak ENSO Activity El Nino Basic State 1 Strong ENSO Activity warms up tropical eastern pacific reduces east-west SST gradient weaken coupling cools down eastern pacific increases SST gradient strngthen coupling El Nino/La Nina asymmetry Reversed ENSO asymmetry

10. basic state changesENSO forcing EOF1 EOF2 Leading EOFs of Low-Pass (>20yrs) Filtered SST Anomalies correlation btw envelope function and low-pass filtered SST anomalies

11. 200mb Velocity Potential Strong-ENSO-Intensity Period Weak-ENSO-Intensity Period Climatology

12. Two-Oscillator View of ENSO Central Pacific Oscillator (related to Asian-Ausatrlian monsoon) Eastern Pacific Oscillator (related to atmos-ocean coupling)

13. 2004-05 El Nino

14. Two Types of ENSO 1997/98 1977/78 Eastern-Pacific ENSO Central-Pacific ENSO

15. Evidence I: Different Decadal Changes in ENSO SST Persistence Barrier

16. 19771988 January August April March July April April/MayApril April/May April Eastern Pacific Central Pacific

17. Decadal Changes of Ocean Heat Content (along equatorial Pacific) 19771988

18. Two-Oscillator View of ENSO Central-Pacific ENSO (related to atmospheric forcing) Eastern-Pacific ENSO (related to thermocline variation)

19. Eastern Pacific Oscillator Central Pacific Oscillator 1 st EOF PC1 correlated with Eq. SSTPower Spectrum of PC1 1 st EOF PC1 correlated with Eq. SSTPower Spectrum of PC1 4 years 5 years ~2 years

20. Power Spectra of Monsoon Rainfall Index Indian Summer MonsoonAustralian Summer Monsoon (modified from Meehl and Arblaster 2002)

21. Local ocean-atmosphere interactions (From Webster 2000)

22. DJF(+1) JJA(+1) JJA(0) Remote ocean-atmosphere interactions - Meehl (1993) (From Meehl 2002)

23. ENSO in CCSM3 Observations CCSM3 Power Spectrum of Nino3.4 Index STD of SST Anomalies Observations CCSM3

24. De-Coupled CCSM3 Experiments Simulated SST replaced by observed climatology

25. Power Spectra of ENSO and Monsoon CCSM3 Control Run ENSO Australian Monsoon Decoupled-IO CCSM3 Run Australian Monsoon ENSO

26. Australian Monsoon Rainfall Index correlates with Surface Winds CCSM3 Control Run EP-type ENSO CP-type ENSO

27. EP-ENSO and Seasonal Cycle 2 yrs SST Seasonal Cycle along Equatorial Pacific Power Spectra of Nino3.4 SST Obs CCSM3 UCLA (from Latif et al. 2001)

28. ENSO Anomalies in Ocean Heat Content EP-type ENSO CP-type ENSO

29. New OHC Index for EP and CP types of ENSO CP-OHC index 160°E-150°W, 5°S-5°N 0-100 meter deep EP-OHC index 80°W-90°W, 5°S-5°N 0-100 meter deep

30. Project NINO3 SST Index (1958-2001) Onto the EP and CP ENSO strong El Niño months strong La Niña months weak event months strong El Nino is EP type strong La Nina is CP type

31. Composite SST Evolution fro strong CP-Type La Niña

32. Summary ENSO can be considered as consisting two oscillators: an Eastern Pacific Oscillator that is driven by air-sea coupling and a Central Pacific Oscillator that is driven by A-A monsoon. The alternations of ENSO between these two oscillators allow the ENSO to interact the Pacific basic state and to give rise to a 10-15year modulation cycle. In CGCMs, the excessive biennial ENSO activity (too strong CPO) and the lack of a 4-year ENSO (too weak EPO) may be two separate issues.

33. ENSO Asymmetry in SST = El Nino + La Nina STRONG ENSO PERIOD WEAK ENSO PERIOD

34. STRONG 120W180120E + _

35. weak 120W180120E _ +

36. Power Spectrum / NINO3 SST / UCLA CGCM Period (month -1 ) Indo-Pacific Ocean Coupling ~2 yrs ~4 yrs Pacific Ocean Coupling Power Density (°C) ~4 yrs 0.02.04.06.08.10 0.02.04.06.08.10.002 0.004.006.008.010.002 0.004.006.008.010 Power Density (°C)

37. Indian Ocean Warming b/a 1976/77 SST Errors in CCSM CTRL Run (1977-1996) minus (1957-1976)

38. ENSO Persistence Barrier in SST

39. Reversed ENSO Impacts on the Basic States Reversed ENSO Impacts on the Basic States (asymmetry in strong period minus asymmetry in weak period) ENSO forcing on SST ENSO forcing on Surface Winds

40. Basin De-Coupling Experiments / NCAR CCSM No Active Indian OceanNo Active Pacific Ocean (simulated January SST) (T42x1 Resolution)

41. NINO 3.4 index CCSM Control Run CCSM Decoupled-Indian-Ocean Run

42. Regression btw ENVF and Filtered SST Leading SST Modes in 10-20year Band

43. Evidence I: Different Decadal Changes in ENSO Persistence Barrier

44. ocean heat content surface zonal wind Decadal Changes of Ocean Heat Content (along equatorial Pacific) shallow thermocline deep thermocline

45. Leading SST Modes in 10-20year Band 2 nd EOF

46. Evidence I: Different Decadal Changes in ENSO SST Persistence Barrier 19771988 January August April March July April April/MayApril April/May April Eastern Pacific Central Pacific