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Influence of Subtropical Air-Sea Interaction on the Multidecadal AMOC Variability in the NCEP CFS

Influence of Subtropical Air-Sea Interaction on the Multidecadal AMOC Variability in the NCEP CFS. Bohua Huang 1 , Zeng-Zhen Hu 2 , Edwin K. Schneider 1 Zhaohua Wu 3 , Yan Xue 2. 1 George Mason University and COLA 2 Climate Prediction Center, NCEP 3 Florida State University.

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Influence of Subtropical Air-Sea Interaction on the Multidecadal AMOC Variability in the NCEP CFS

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  1. Influence of Subtropical Air-Sea Interaction on the Multidecadal AMOC Variability in the NCEP CFS Bohua Huang1, Zeng-Zhen Hu2, Edwin K. Schneider1 Zhaohua Wu3, Yan Xue2 1George Mason University and COLA 2Climate Prediction Center, NCEP 3Florida State University

  2. Scientific Questions • What role does the ocean-atmosphere interaction play in the multidecadal AMOC oscillation? • Does the tropical-subtropical Atlantic Ocean also play a part in the multidecadal AMOC oscillation?

  3. CFS Simulation • CFS-v1, operational system for seasonal to interannual prediction at NCEP since August 2004 • Atmospheric component: GFS (2003), T62 (~200 km), 64 sigma levels (prescribed sea ice cover affects surface flux into the ocean) • Oceanic component: MOM3, 1ox1o (1/3o lat within 10oS-10oN), 40 levels, non-polar (70oS-65oN) no transport between Atlantic and Arctic Ocean no sea-ice formation mechanism • Daily coupling over active ocean domain (without flux correction) • Initial condition: January 1, 1985, Atmosphere: NCEP Reanalysis 2; Ocean: GODAS • Integration is ongoing, 400-yrs done

  4. AMOC Index Year-to-Year Interannual Decadal Multidecadal Century

  5. AMOC Index Year-to-Year Interannual Decadal Multidecadal Multidecadal + Century

  6. Leading MSSA (EXEOF) Modes, 5-yr Running Mean 30-Year Lags MSSA1 -PC1 -EEMD C Century Mode MSSA 1(22.3%) -PC1 -EEMD M Multidecadal Mode MSSA2-3 (7.6%+6.4%) MSSA2-3

  7. Multi-Decadal Mode

  8. Multi-Decadal Mode

  9. Multi-Decadal Mode

  10. Multi-Decadal Mode

  11. Multi-Decadal Mode

  12. cm/s

  13. AMOC Feedback Loops Strong AMOC Warm HC, SST around 30o-45oN Wind curl (-) Downwelling Strong AMOC Weak Subtr. High Warm Subtr. SST Weak N.E. Trade Wind Delayed AMOC Weakening Cold Subtr.HC Weak STC Wind Curl (+) Subtr.Upwelling

  14. AMOC leads AMOC lags

  15. Summary • AMOC fluctuates on a wide range of time scales in CFS. • An intermittent multidecadal (30-yr) oscillation is generated by ocean-atmosphere feedback within the Atlantic sector. • Delayed response of the northern subtropical cell is crucial for the oscillation.

  16. Leading MSSA (EXEOF) Modes, Seasonal mean Lag 20 seasons (5-yrs) MSSA1-2 (3.7%+3.6%) EOF1 EOF2 68.2% 28.4% ENSO Mode PC1 COR 0.57 NINO3 lags 1 season —Normalized NINO3 index PC2 COR 0.52 NINO3 leads 5 seasons

  17. ENSO Mode

  18. ENSO Mode

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