Atlantic Meridional Overturning Circulation and the Prediction of North Atlantic Sea Surface...
If you can't read please download the document
Atlantic Meridional Overturning Circulation and the Prediction of North Atlantic Sea Surface Temperature Mojib Latif, Helmholtz Centre for Ocean Research
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.
Slide 2
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?
Slide 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
Slide 4
The NAO drives convection in the North Atlantic, which in turn
drives the AMOC Latif and Keenlyside 2011
Slide 5
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
Slide 6
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
Slide 7
Surface air temperature anomalies associated with
multicentennial and multidecadal AMOC variability largely
independent and originating in different regions multicentennial
multidecadal Park and Latif 2008
Slide 8
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
Slide 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
Slide 10
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
Slide 11
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
Slide 12
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
Slide 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 AMOC leads observed
North Atlantic SST by 1-2 decades, use model (KCM) AMOC to predict
observed SST Klwer et al. 2014
Slide 14
Leading CCA modes SST leads AMOC by 10 years SST lags AMOC by
21 years Klwer et al. 2014
Slide 15
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
Slide 16
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
Slide 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.
Slide 18
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
Slide 19
Comparison of model SST with observed SST by means of Canonical
Correlation Analysis (CCA) time series, CCA-mode 2
Slide 20
Comparison of model SST with observed SST by means of Canonical
Correlation Analysis (CCA) patterns, CCA-mode 2
Slide 21
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
Slide 22
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
Slide 23
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
Slide 24
Hindcast of the AMOC 1900-2010 Kiel Climate Model forced by
NAO-related heat flux anomalies overturning at 48Noverturning at
48N, 1500m
Slide 25
Lag-regression of model SST w.r.t. AMOC index at 30N SST
anomaly patterns are strongly influenced by model bias
Slide 26
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
Slide 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
Slide 28
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
Slide 29
Comparison of model SST with observed SST by means of Canonical
Correlation Analysis (CCA) time series, CCA-mode 1
Slide 30
Comparison of model SST with observed SST by means of Canonical
Correlation Analysis (CCA) patterns, CCA-mode 1 observed SSTmodel
SST
Slide 31
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
Slide 32
NAO-forced mixed-layer depth and AMOC variability corr.: NAO
with mixed-layer depth corr.: mixed-layer depth with AMOC
Slide 33
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