multi-decadal variability of atlantic meridional ...€¦ · ocean circulation feedback from the...
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Multi-decadal Variability of Atlantic Meridional Overturning Circulation
in CCSM3 T85x1 Control Integration
Young-Oh Kwon
(Woods Hole Oceanographic Institution)
Co-author: Claude Frankignoul (LOCEAN, Université Pierre et Marie Curie, Paris)
CCSM Annual Meeting OMWG (Breckenridge, CO; June 16, 2009)
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CCSM3 T85x1 Control Integration AMOC
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Atmosphere: North Atlantic Oscillation (NAO)
Regime I(Model Year: 150-399)
Regime II(Model Year: 450-699)
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AMOC Leading Empirical Orthogonal Function (EOF)
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AMOC Time Series (= PC 1 Time Series)Power Spectrum & Auto-Correlation
~ Red noise Long persistence (~10 years)
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AMOC Regression on NAO(low-pass filtered > 10 years)
(Contour Interval = 0.1 Sv)
AMOC integrates NAO forcing Short persistence (< 5 years)
Positive Lags: NAO Leads
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AMOC PC-1 & Deep Convection: Lag-Correlation(Deep Convection Time Series: Upper 500 m Density in the Convection Site)
AMOC integrates the convection variability
Hint of weak positive feedback
Long Persistence (~10 years)
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Upper 500 m Density Correlation with Deep Convection
Positive Lags: Deep Convection Leads (Contour Interval = 0.2)
Gulf Stream – North Atlantic Current northward shift
Positive Feedback due to increased subpolar waterDeep Convection Site
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Horizontal Circulation Regression on Deep Convection
Anti-clockwise circulation intensification
Gulf Stream – North Atlantic Current northward shift
Positive Lags: Deep Convection Leads (Contour Interval = 1 Sv)
(Contour Interval = 10 Sv)
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Convection and Horizontal Circulation (at NAC box)
Hint of 20-year oscillation
Auto-CorrelationsLag-Correlation
NAC BSF lags and integrates convection
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Alternative Possibility :Feedback between the convection and horizontal circulation
Upper 500m density correlated on convection index
Auto-correlation of convection index
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Mean Barotropic Streamfunction
(Contour Interval = 10 Sv, 10 Sv, 2 Sv)
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Conclusions
Regime II AMOC variability• Short Persistence (< 5 years)
: Stochastic atmospheric NAO forcingNAO ⇒ Deep convection ⇔ Anti-clockwise Gyre ⇒ AMOC(Please see the poster!)
• Long Persistence (~10 years) : Ocean circulation feedback from the eastern subpolar gyreDeep Convection ⇔ GS/NAC Circulation ⇔ AMOC
Factors to be considered for the Regime I AMOC variability • Ocean-to-atmosphere feedback
• Strength and location of Gulf Stream / North Atlantic Current
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Climate Change Simulations using CCSM3
Lower resolutionT31x3
Medium resolutionT42x1
Higher resolutionT85x1
Control Integration
Transient Integration A(1% per year Increasing CO2)
Transient Integration B(1% per year Increasing CO2)
Double CO2 Stabilization
Quadruple CO2 Stabilization
Bryan et al. (2006)
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Thank You