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ENSO Variability in SODA: 1871-2008

ENSO Variability in SODA: 1871-2008. SULAGNA RAY BENJAMIN GIESE TEXAS A&M UNIVERSITY WCRP 2010, Paris, 17-19 Nov. 2010. Historical Winds. Compo et al., BAMS, 2006. Comparison of NINO 4 zonal wind stress between 20CRv2 and ERA-40. Black : 20CRv2 Red : ERA-40. SODA 2.2.4.

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ENSO Variability in SODA: 1871-2008

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  1. ENSO Variability in SODA: 1871-2008 SULAGNA RAY BENJAMIN GIESE TEXAS A&M UNIVERSITY WCRP 2010, Paris, 17-19 Nov. 2010

  2. Historical Winds Compo et al., BAMS, 2006

  3. Comparison of NINO 4 zonal wind stress between 20CRv2 and ERA-40 Black : 20CRv2 Red : ERA-40

  4. SODA 2.2.4 • Model • − Parallel Ocean Program 2.0.1 • Domain • − Global (including Arctic) • Resolution • − 0.4° × 0.25° average resolution • − 40 levels, 10m spacing from surface to 450m • Winds • − 20CRv2 daily stress 1871-2008 • Heat and Salt fluxes • − Bulk formulae using 20CRv2 daily variables • SODA Data Assimilation • − WOD09 hydrographic and ICOADS 2.5 SST data

  5. DJF SST anomaly of two strong El Niños from HadISST & SODA 2.2.4 HADISST SODA 2.2.4 1877 1997

  6. hhhhh Standard Measure of El Niño : NINO-3.4 SST anomaly NINO-3.4 SST anomaly from SODA 2.2.4 (Red) and HADISST (Black) Stronger El Niños in SODA compared to HADISST

  7. NINO-3.4 Index DJF SST anomaly of 1997-98 El Niño

  8. Center of Heat Index : CHI First moment of SST anomaly - Like the center of mass SST anomaly must be greater than 0.5°C Area must be greater or equal to the NINO-3.4 region CHI Longitude = center of El Niño warming CHI Amplitude = strength of El Niño Same for La Niña

  9. CHI- Amplitude showing strength of El Niños Amplitude (C) Years El Niño in the late 19th century as strong as those in late 20th century

  10. CHI- Amplitude showing strength of La Niña Amplitude (C) Years La Niña in the last century do not show much variation

  11. CHI-Longitude showing Location of El Niños Longitude Years Circle radius proportional to the strength of CHI-amplitude

  12. An Analysis of the position of El Niño in SODA • Histogram of the position overlayed by a Gaussian with same mean and standard deviation • Null hypothesis: Position of El Niño randomly distributed about 140W

  13. Obstacles in Ocean reanalysis • Ocean observations are inhomogenous in space and time • - Data thinning experiment ✔ • Model bias • - Simulation vs. Assimilation ✔ • Errors in surface forcing

  14. WOD09 Hydrographic Temperature Observations 1920s 1940s 1960s 1990s Per decade

  15. ICOADS 2.5 Number of SST Observations Per decade

  16. Data Thinning Experiment Sample the 1990s as though sampled in different periods 5 Experiments : 1.) No Assimilation As though sampled in the 2.) 1920s 3.) 1940s 4.) 1960s 5.) 1990s – Control run All other elements of the run are identical

  17. SST RMS Difference in the Tropical Pacific Value in assimilating even sparse observations

  18. Model Bias in CHI-Amplitude and Longitude Red− Before 1950 Blue− After 1950 SODA 2.2.0 CHI-Longitude SODA 2.2.0 CHI-Amplitude SODA 2.2.4 CHI-Longitude SODA 2.2.4 CHI-Amplitude • Bias in the model does not seem to affect the amplitude of El Niño events • There is a slight westward bias in the position of the El Niño

  19. Comparison of CHI from SODA and HadISST Red− Before 1950 Blue− After 1950 HADISST CHI-Amplitude HADISST CHI-Longitude SODA 2.2.4 CHI-Amplitude SODA 2.2.4 CHI-Longitude • El Niños are warmer in SODA compared to HadISST before 1950 • El Niños in HadISST are east of those in SODA for the post-1950 period • No correlation before1950 in terms of location

  20. Conclusions • A 138-yr reanalysis is used to explore ENSO variability • First moment of temp. anomaly (CHI) is used to describe El Niño • Prominent decadal variability of El Niño strength, but little trend • Location of El Niño varies considerably… But the distribution cannot • be distinguished from Gaussian • Model bias in SODA does not significantly affect the strength of El Niño but • does introduce a slight westward bias in location • Assimilation of sparse data adds value to the reanalysis

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