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Decadal Modulation of ENSO and Basic State Interactions

This study examines the decadal modulation of ENSO intensity and its interactions with the basic state of the Pacific. The analysis includes the NINO3.4 SST index, ERSST.v2 data, and HadISST dataset from 1870 to 2006. It explores the oscillatory nature of ENSO, its relationship with Asian-Australian monsoon and thermocline variation, and the impact on ocean heat content and monsoon rainfall. The study also investigates the asymmetry in ENSO activity and its persistence barrier. The findings provide insights into the complex interactions and forcing mechanisms of ENSO.

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Decadal Modulation of ENSO and Basic State Interactions

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

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

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

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

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

  6. Power Spectrum of the Envelope Function HadISST (1870-2006) ERSST.v.2 (1880-2006) Mann et al. (1650-1980)

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

  8. Warm El Niño Cold La Niña _ STRONG + + - Warm El Niño Cold La Niña _ weak + - + ENSO forcing basic state changes

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

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

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

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

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

  16. July April March April/May April April April/May April April 1977 1988 Evidence I: Different Decadal Changes in ENSO SST Persistence Barrier August April January Eastern Pacific Central Pacific

  17. Decadal Changes of Ocean Heat Content(along equatorial Pacific) 1977 1988

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

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

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

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

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

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

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

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

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

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

  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 Nino is EP type • strong El Niño months • strong La Niña months • weak event months 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 120W 180 120E _ +

  35. weak 120W 180 120E _ +

  36. Power Spectrum / NINO3 SST / UCLA CGCM Indo-Pacific Ocean Coupling Pacific Ocean Coupling .010 .010 .008 .008 ~4 yrs ~4 yrs .006 .006 Power Density (°C) Power Density (°C) .004 .004 ~2 yrs .002 .002 0 0 .04 .06 .08 .10 .04 .06 .08 .10 .02 .02 0 0 Period (month-1) Period (month-1)

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

  38. ENSO Persistence Barrier in SST

  39. 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 (T42x1 Resolution) No Active Indian Ocean No Active Pacific Ocean (simulated January SST) (simulated January SST)

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

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

  46. July April March April/May April April April/May April April 1977 1988 Evidence I: Different Decadal Changes in ENSO SST Persistence Barrier August April January Eastern Pacific Central Pacific

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