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Impact of Ensemble Size on Significance of Climate Change, Variability, and Extremes

Impact of Ensemble Size on Significance of Climate Change, Variability, and Extremes. Jeff Yin, NCAR 11 th CCSM Workshop 22 June 2006. Examples of the Impact of Ensemble Size. Climate change (2080-2099 – 1980-1999): Stationary waves/zonal means Midlatitude storm tracks

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Impact of Ensemble Size on Significance of Climate Change, Variability, and Extremes

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  1. Impact of Ensemble Size on Significance of Climate Change, Variability, and Extremes Jeff Yin, NCAR 11th CCSM Workshop 22 June 2006

  2. Examples of the Impact of Ensemble Size • Climate change (2080-2099 – 1980-1999): • Stationary waves/zonal means • Midlatitude storm tracks • Seasonal maximum wind speed • Climate variability (NAO): • Seasonal maximum wind speed • Percentiles of wind speed • 95% significance level shown

  3. 2080-2099 minus 1980-1999:Total Z300

  4. 2080-2099 minus 1980-1999:Total Z300

  5. 2080-2099 minus 1980-1999:Total Z300

  6. 2080-2099 minus 1980-1999:Stationary wave Z300

  7. 2080-2099 minus 1980-1999:Stationary wave Z300

  8. 2080-2099 minus 1980-1999:Stationary wave Z300

  9. 2080-2099 minus 1980-1999:Zonal mean Z300

  10. 2080-2099 minus 1980-1999:Zonal mean Z300

  11. 2080-2099 minus 1980-1999:2-8 day EKE200

  12. 2080-2099 minus 1980-1999:2-8 day EKE200

  13. 2080-2099 minus 1980-1999:Seasonal maximum daily WS850

  14. 2080-2099 minus 1980-1999:Seasonal maximum daily WS850

  15. 2080-2099 regression on NAO:Seasonal maximum daily WS850

  16. 2080-2099 regression on NAO:Seasonal maximum daily WS850

  17. Positive NAO, 2080-2099:99%ile of WS850

  18. Positive NAO, 1870-1999:99%ile of WS850

  19. Positive NAO, 1870-1999:99.9%ile of WS850

  20. Summary • Ensemble size needs depend on problem • For differences of 20-year periods: • 1 member not enough (even for zonal mean) • 4+ members for stationary waves • 4+ members for storm tracks, extreme winds • For relationships with NAO: • 4+ members for seasonal max wind speed • > 300 years for 99%ile of wind speed

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