Mojib Latif , Helmholtz Centre for Ocean Research and Kiel University

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

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Dynamics of Predictability of the AMOC Mojib Latif, Helmholtz Centre for Ocean Research and Kiel University

Atlantic Meridional Overturning Circulation and thePrediction of North Atlantic Sea Surface TemperatureMojib Latif, Helmholtz Centre for Ocean Research and Kiel UniversityKlwer, M., et al. (2014) Earth and Planetary Science Letters, 406, DOI 10.1016/j.epsl.2014.09.001.

Scientific QuestionsWhat is the role of the AMOC in decadal North Atlantic SST variability?How predictable is the AMOC-related North Atlantic SST variability?How can we deal with model bias which is particularly large in the North Atlantic?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

The NAO drives convection in the North Atlantic, which in turn drives the AMOC

Latif and Keenlyside 2011The Kiel Climate Model (KCM)

El Nio/Southern Oscillation(ENSO), period ~4 yrsAtlantic Multidecadal Oscillation (AMO/V), period ~60 yrsPacific Decadal Oscillation (PDO/V), period ~50 yrsSouthern Ocean Centennial Variability (SOCV), ~ 300 yrsThe Kiel Climate Model (KCM) simulates rich internal AMOC variability in a 4,000 years long control run

AMOC index, 30NPark and Latif 2008Surface air temperature anomalies associated with multicentennial and multidecadal AMOC variabilitylargely independent and originating in different regions

multicentennialmultidecadalPark and Latif 2008

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 modeThe Kiel Climate Model (KCM) is forced by NAO-related heat flux anomaliesQnet

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

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

11-year running means2. Dynamical/statistical prediction of the decadal North Atlantic SST variabilityModel bias is large. We cant expect that the model realistically simulates North Atlantic SST variability linked to AMOC variability

The issue of model bias

AMOC variability in the KCM 1870-2000model overturning variabilityCanonical Correlation Analysis (CCA) was used to statistically relate the overturning variability to the observed North Atlantic SST variability

Klwer et al. 2014

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

Leading CCA modesSST leads AMOC by 10 yearsSST lags AMOC by 21 yearsKlwer et al. 2014Link 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 yearsKlwer et al. 2014suggests a rather high decadal predictability potential

Statistical hindcast/forecast of the observed AMO index using the model AMOC as a predictorthe present AMO warm phase will continue until 2030, but with negative tendencyr=0.69Klwer et al. 20143. 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.ConclusionsThe NAO is an important driver of the AMOC, which was shown by forcing the KCM by NAO-related heat fluxesThis method could be an alternative to initialize decadal predictions, as climate models suffer from large biases The KCMs AMOC can be used as a predictor to statistically predict with high skill decadal North Atlantic SST variabilityThis study suggests a rather high decadal predictability potential of North Atlantic SST, which solely arises from the history of the NAOThe AMO/V is predicted to stay in its warm phase until 2030, but with a negative tendencyComparison of model SST with observed SST by means of Canonical Correlation Analysis (CCA)time series, CCA-mode 2

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

Verification of the Bjerknes hypothesis: atmosphere drives NA SST on short, ocean on long time scalescorrelation SST/Q, low-passcorrelation SST/Q, high-passcutoff at about 10 yearsGulev et al. 2013The individual surface heat flux components from reanalysis

the turbulent fluxes matter, radiative fluxes are weak, which argues against aerosol forcing of multidecadal SST variabilityQSHQLHQSWQLWEvolution of the overturning streamfunction anomaly with respect to the NAO in the KCM

the climate model acts as a complicated filter on the NAO-forcingHindcast of the AMOC 1900-2010

Kiel Climate Model forced by NAO-related heat flux anomaliesoverturning at 48N

overturning at 48N, 1500mLag-regression of model SST w.r.t. AMOC index at 30N

SST anomaly patterns are strongly influenced by model biasThe problem of model bias, or why we cant use the predicted model SST

CMIP5 multi-model mean SST biascourtesy S. Steinigincorrect path of North Atlantic Current inhibitsrealistic simulation of SSTThe role of wind stress forcing

skill in hindcasting observed SST when prescribing observed wind stress anomalies to the KCMcorrelations based on annual meansAnalysis 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

Comparison of model SST with observed SST by means of Canonical Correlation Analysis (CCA)

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

patterns, CCA-mode 1observed SSTmodel SSTThe individual surface heat flux components from reanalysis

the turbulent fluxes matter, radiative fluxes are weak, which argues against aerosol forcing of multidecadal SST variabilityQSHQLHQSWQLWNAO-forced mixed-layer depth and AMOC variability

corr.: NAO with mixed-layer depth corr.: mixed-layer depth with AMOCThe research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299NACLIM www.naclim.eu

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