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
10.1016/j.epsl.2014.09.001.
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?
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 2011
The Kiel Climate Model (KCM)
1. El Niño/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
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
Surface air temperature anomalies associated with
multicentennial and multidecadal AMOC variability
multicentennial
multidecadal
largely independent and originating in different regions
Park and Latif 2008
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
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
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
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
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
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
Leading CCA modes
SST leads AMOC by 10 years
SST lags AMOC by 21 years
Klöwer et al. 2014
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
Statistical hindcast/forecast of the observed AMO
index using the model AMOC as a predictor
r=0.69
Klöwer et al. 2014
the present AMO warm phase will continue until 2030,
but with negative tendency
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.
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 KCM’s 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
Comparison 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 scales
correlation SST/Q, low-pass
correlation SST/Q, high-pass
Gulev et al. 2013
cutoff at about 10 years
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
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
Hindcast of the AMOC 1900-2010
Kiel Climate Model forced by NAO-related heat flux anomalies
overturning atoverturning
48°N
at 48°N, 1500m
Lag-regression of model SST w.r.t. AMOC index at 30°N
SST anomaly patterns are strongly influenced by model bias
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
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
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
Comparison of model SST with observed SST by
means of Canonical Correlation Analysis (CCA)
time series, CCA-mode 1
Comparison of model SST with observed SST by
means of Canonical Correlation Analysis (CCA)
patterns, CCA-mode 1
observed SST
model SST
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
NAO-forced mixed-layer depth and AMOC variability
corr.: NAO with mixed-layer depth
corr.: mixed-layer depth with AMOC
•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