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Atlantic Meridional Overturning Circulation and the Prediction of North Atlantic Sea Surface Temperature Mojib Latif, Helmholtz Centre for Ocean Research and Kiel University Klwer, M., et al. (2014) Earth and Planetary Science Letters, 406, DOI 10.1016/j.epsl.2014.09.001.

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Scientific Questions 1.What is the role of the AMOC in decadal North Atlantic SST variability? 2.How predictable is the AMOC-related North Atlantic SST variability? 3.How can we deal with model bias which is particularly large in the North Atlantic?

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1. What is the role of the AMOC in decadal North Atlantic SST variability? hypothesis: low-frequency variability of the NAO drives the AMOC (following Eden and Jung 2001) through anomalous surface heat fluxes

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The NAO drives convection in the North Atlantic, which in turn drives the AMOC Latif and Keenlyside 2011

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The Kiel Climate Model (KCM) 1.El Nio/Southern Oscillation(ENSO), period ~4 yrs 2.Atlantic Multidecadal Oscillation (AMO/V), period ~60 yrs 3.Pacific Decadal Oscillation (PDO/V), period ~50 yrs 4.Southern Ocean Centennial Variability (SOCV), ~ 300 yrs

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The Kiel Climate Model (KCM) simulates rich internal AMOC variability in a 4,000 years long control run AMOC index, 30N Park and Latif 2008

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Surface air temperature anomalies associated with multicentennial and multidecadal AMOC variability largely independent and originating in different regions multicentennial multidecadal Park and Latif 2008

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The KCM (T31-L19, 2) is used to assess the impact of the NAO-related heat fluxes on the AMOC the anomalous heat flux forcing is applied to a coupled model, which distorts the thermodynamic feedbacks less than when forcing ocean models in uncoupled mode The Kiel Climate Model (KCM) is forced by NAO-related heat flux anomalies Q net

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Hypothesis: NAO-related heat flux anomalies drive the AMOC which in turn drives North Atlantic SST a positive phase of the NAO is associated with an enhanced heat loss over the subpolar North Atlantic

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Kiel Climate Model (KCM) response when forced by NAO-related heat fluxes NAO index is in phase with mixed layer depth and subpolar gyre, but leads the models AMOC by several years 11-year running means

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2. Dynamical/statistical prediction of the decadal North Atlantic SST variability Model bias is large. We cant expect that the model realistically simulates North Atlantic SST variability linked to AMOC variability The issue of model bias

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AMOC variability in the KCM 1870-2000 model overturning variability Canonical Correlation Analysis (CCA) was used to statistically relate the overturning variability to the observed North Atlantic SST variability Klwer et al. 2014

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CCA has been performed between model AMOC and observed North Atlantic SST CCA finds those patterns in two datasets, with time evolutions that are most strongly correlated AMOC leads observed North Atlantic SST by 1-2 decades, use model (KCM) AMOC to predict observed SST Klwer et al. 2014

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Leading CCA modes SST leads AMOC by 10 years SST lags AMOC by 21 years Klwer et al. 2014

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Link between model AMOC and observed SST at two leads/lags expressed by the leading CCA modes SST leads AMOC by 10 yearsSST lags AMOC by 21 years Klwer et al. 2014 suggests a rather high decadal predictability potential

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Statistical hindcast/forecast of the observed AMO index using the model AMOC as a predictor the present AMO warm phase will continue until 2030, but with negative tendency r=0.69 Klwer et al. 2014

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3. How can we deal with model bias which is particularly large in the North Atlantic? either by improving the models (tough!) or by correction methods: flux correction, flow field correction Drews et al., in prep.

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Conclusions 1.The NAO is an important driver of the AMOC, which was shown by forcing the KCM by NAO-related heat fluxes 2.This method could be an alternative to initialize decadal predictions, as climate models suffer from large biases 3.The KCMs AMOC can be used as a predictor to statistically predict with high skill decadal North Atlantic SST variability 4.This study suggests a rather high decadal predictability potential of North Atlantic SST, which solely arises from the history of the NAO 5.The AMO/V is predicted to stay in its warm phase until 2030, but with a negative tendency

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Comparison of model SST with observed SST by means of Canonical Correlation Analysis (CCA) time series, CCA-mode 2

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Comparison of model SST with observed SST by means of Canonical Correlation Analysis (CCA) patterns, CCA-mode 2

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Verification of the Bjerknes hypothesis: atmosphere drives NA SST on short, ocean on long time scales correlation SST/Q, low-passcorrelation SST/Q, high-pass cutoff at about 10 years Gulev et al. 2013

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The individual surface heat flux components from reanalysis the turbulent fluxes matter, radiative fluxes are weak, which argues against aerosol forcing of multidecadal SST variability Q SH Q LH Q SW Q LW

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Evolution of the overturning streamfunction anomaly with respect to the NAO in the KCM the climate model acts as a complicated filter on the NAO-forcing

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Hindcast of the AMOC 1900-2010 Kiel Climate Model forced by NAO-related heat flux anomalies overturning at 48Noverturning at 48N, 1500m

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Lag-regression of model SST w.r.t. AMOC index at 30N SST anomaly patterns are strongly influenced by model bias

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The problem of model bias, or why we cant use the predicted model SST CMIP5 multi-model mean SST bias courtesy S. Steinig incorrect path of North Atlantic Current inhibits realistic simulation of SST

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The role of wind stress forcing skill in hindcasting observed SST when prescribing observed wind stress anomalies to the KCM correlations based on annual means

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Analysis of North Atlantic turbulent surface heat fluxes since 1880 suggests that the ocean drives North Atlantic SST at decadal time scales Gulev et al. 2013

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Comparison of model SST with observed SST by means of Canonical Correlation Analysis (CCA) time series, CCA-mode 1

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Comparison of model SST with observed SST by means of Canonical Correlation Analysis (CCA) patterns, CCA-mode 1 observed SSTmodel SST

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The individual surface heat flux components from reanalysis the turbulent fluxes matter, radiative fluxes are weak, which argues against aerosol forcing of multidecadal SST variability Q SH Q LH Q SW Q LW

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NAO-forced mixed-layer depth and AMOC variability corr.: NAO with mixed-layer depth corr.: mixed-layer depth with AMOC

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The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu