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

2. Scientific Questions
What 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?

3. 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

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

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

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

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

8. The KCM (T31-L19, 2°) is used to assess the impact of the NAO-related heat fluxes on the AMOC
The Kiel Climate Model (KCM) is forced by NAO-related heat flux anomalies
Q’net
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

9. 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

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

11. 2. Dynamical/statistical prediction of the decadal North Atlantic SST variability
The issue of model bias
Model bias is large. We can’t expect that the model realistically simulates North Atlantic SST variability linked to AMOC variability

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

13. 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
Klöwer et al. 2014
AMOC leads observed North Atlantic SST by 1-2 decades, use model (KCM) AMOC to predict observed SST

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

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

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

17. 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.

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

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

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

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

22. The individual surface heat flux components from reanalysis
QLH
QSH
QLW
QSW
the turbulent fluxes matter, radiative fluxes are weak, which argues against aerosol forcing of multidecadal SST variability

23. the climate model acts as a complicated filter on the NAO-forcing
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

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

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

26. The problem of model bias, or why we can’t 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

27. 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

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

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

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

31. The individual surface heat flux components from reanalysis
QLH
QSH
QLW
QSW
the turbulent fluxes matter, radiative fluxes are weak, which argues against aerosol forcing of multidecadal SST variability

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

33. The research leading to these results has received funding from the European Union 7th Framework Programme (FP ), under grant agreement n
NACLIM