1. S. Gualdi, A. Bellucci, R. Mathew, E. Scoccimarro
INGV
ISTITUTO NAZIONALE di
GEOFISICA e VULCANOLOGIA
Climate variability and change in the Euro-Mediterranean region as simulated with a global climate model
S. Gualdi, A. Bellucci, R. Mathew, E. Scoccimarro
INGV-CMCC

2. OBJECTIVE & MOTIVATION
Regional climate changes can differ substantially from the global change
projection and the assessment of the regional patterns of climate change
is one of the principal goal of the research activity
Regional climate change projections are generally produced with:
1) statistical down-scaling (strong assumptions large scale-small scale)
2) dynamical down-scaling: regional climate models (RCM) forced by large-
scale background flow from global models generally at low-resolution (no feedbacks)
3) high-resolution atmospheric-only GCMs forced with SSTs obtained from
low-resolution coupled model scenarios (no feedbacks)
Recent (IPCC) climate scenario simulations performed with high-resolution
global CGCMs (e.g., GFDL, INGV and MIROC) allow some detailed
analyses of the regional patterns of climate change including (in principle)
all the feedback processes

3. horizontal resolution ~ 120Km INGV-IPCC runs
horizontal resolution ~250/300 Km IPCC-AR4 standard 3

4. OBJECTIVE & MOTIVATION
Main features of the regional (Euro-Mediterranean) patterns
of climate change produced with a global, high-resolution,
state of the art coupled model will be discussed
Implications for the next challenges that will be faced in the
field of climate change simulations: short-term projections
(multi-decadal climate prediction experiments)
DATA
Observations: ERA-40 re-analyses ( ),
CMAP (Xie-Arkin) precipitation ( )
Simulations: IPCC scenarios: 20th Century ( ), A2 ( )
data available at the PCMDI archive (

5. INGV-CMCC COUPLED MODEL SINTEX-G (SXG)
Gualdi et al. 2006
Gualdi et al. 2008
Bellucci et al. 2008
ECHAM-4.6:
Max-Planck-Inst. Hamburg
Global, T106 resolution (1.1ºx1.1º)
19 Vertical levels
Atmosphere
Coupler
Ocean
&
Sea-Ice
OASIS 2.4
Coupling every 1.5 hours
No Flux Adjustment
OPA 8.2:
LODYC, Paris,
Global, Resol -> 2º longitude
0.5º - 2º latitude
31 Vertical Levels
Lim:
UCL, Louvain-la-Neuve,
3-layer model
Dyn & Thermodyn

6. 20th Century EURO-MEDITERRANEAN Precipitation 2m-Temperature
Observations
Model
Observations
Model
JFM
AMJ
JAS
OND
mm/day °C
Precipitation
2m-Temperature

7. SCENARIO: A2 – 20C 2m-Temperature
A2( ) – 20C( ) JFM
A2( ) – 20C( ) JFM
A2( ) – 20C( ) JAS
A2( ) – 20C( ) JAS °C

8. SCENARIO: A2 – 20C precipitation
A2( ) – 20C( ) JFM
A2( ) – 20C( ) JFM
A2( ) – 20C( ) JAS
A2( ) – 20C( ) JAS
mm/day

9. SUMMARY 1
The Euro-Med region undergoes a substantial warming in all
season. Warming is maximum over the north-east Europe in
winter and south-western Europe-Mediterranean in summer
In summer precipitation decreases over most of the Euro-
Med. In winter it increases over north Europe and decreases
over south Europe and the Mediterranean
These results are fully consistent with the results obtained
with several other CGCMs (IPCC-AR4)

10. Implications for the short-term climate projections (multi-decadal
climate prediction experiments)
Similarities between the regional patterns of climate change and the variability
associated with the NAO
Precipitation
A2( ) – 20C( ) JFM
NAO +
To which extent can we discriminate between the climate change
signal and the anomalies induced by the natural variability (NAO)
in the short-term climate prediction experiments?

11. According to a simple interpretation (climate noise paradigm) the relevant space-time scales of NAO are determined by processes which are internal to the atmosphere
NAO -
NAO +

12. Among the external forcings which may potentially affect the NAO
However, there are also evidences of a departures from a red noise hypothesis: the spectrum of the observed NAO shows enhanced power around multi-annual (decadal) time-scales, suggesting the possible involvement of external factors which modulate the NAO activity
Power spectrum of Z300 PC1
(Feldstein, 2000)
red noise
Among the external forcings which may potentially affect the NAO
variability what is the role of the ocean?

13. NAO and North Atlantic variability
SXG 20C
NAO and North Atlantic variability
(Bellucci et al. 2008)
SXG SLP EOF1 (34%)
Power Spectra
SXG SST Tripole
OBS NAOI
SXG NAOI
SXG SST EOF1 (30%)
SST PC1

14. SST Composite maps (keyed to the SST PC1)
Re-emergence of the tripole in a 5 years time .
Thermal inertia of the mixed layer accounts for an ocean memory of a few months (Frankignoul et al. 1998). If the tripole reappears (instead of undergoing an exponential decay) an additional process must be at work.

15. 200-hPa Z and SST Composite maps
(keyed to the SST PC1)
GPH c.i.: 5 m

16. The NAO forces a gyre circulation anomaly which enhances the inter-gyre gyre transfer of SST anomalies
Composite of JFM wind stress: NAO+ minus NAO-
Ψ EOF1:Inter-gyre gyre (IGG)
Inter-gyre gyre: consistent with the barotropic streamfunction anomaly driven by NAO wind-curl as predicted by Sverdrup balance:

17. SST/NAO interaction occurs through anomalous wind-driven circulation consistent
with Marshall et al. (2001) paradigm for mid-latitude coupled variability
During a NAO+ phase the IGG contributes to the warming of high latitudes, hence weakening the SST meridional gradient
wind
IGG -
Subtropical/subpolar
gyre boundary
NAO +
sst +
Once the northern SST dipole has reversed its sign, there are favourable conditions
for the NAO to enter into a negative phase
wind
IGG +
NAO -
Subtropical/subpolar
gyre boundary -
sst

18. Results from a CGCM suggest that midlatitude variability in
SUMMARY 2
Results from a CGCM suggest that midlatitude variability in
the North Atlantic on multi-annual time-scales is determined
by an oscillatory mode involving co-varying changes in SST
and atmospheric circulation with a typical NAO-like pattern
(Bellucci et al. 2008)
These results are qualitatively consistent with the delayed-
oscillator paradigm of a coupled mode of variability of the
North Atlantic proposed by Marshall et al. (2001)
The possible existence of a coupled SST-NAO mode of
variability active at multi-annual time-scales would be of
great importance for the study of climate variability and
climate change in the Euro-Mediterranean region and,
more generally, of relevance for the feasibility short-term
climate projection experiments

19. Thanks!

20. THE SCENARIO SIMULATIONS
global mean surface temperature anomaly

21. SST Precip SST Precip 20th Century MODEL PERFORMANCE: GLOBAL JJASO
Observations
Model
SST
JJASO
MEAN
Precip
SST
DJFMA
MEAN
Precip

22. JFM STANDARD DEVIATION 2m-Temperature OBSERVATIONS (1958-2001)
SXG 20C ( ) °C
SXG A2 ( )
SXG A2 ( ) °C

23. JAS STANDARD DEVIATION 2m-Temperature OBSERVATIONS (1958-2001)
SXG 20C ( )
SXG A2 ( )
SXG A2 ( ) °C

24. TELECONNECTIONS: NAO
OBS
JFM
anomaly regression NAO index °C
mm/day 24

25. SXG 20C JFM TELECONNECTIONS: NAO anomaly regression NAO index °C 25
mm/day 25

26. SXG A2 JFM TELECONNECTIONS: NAO anomaly regression NAO index °C 26
mm/day 26

27. Year 3
Year +3
Year +2
Year 2
Year +1
Year 1
Year 0
Year 0
SINTEX-G
Sutton and Allen, 1997

28. The anomalous gyre circulation response to the NAO wind-stress
Composite of JFM wind stress :NAO+ minus NAO-
Ψ EOF1:Inter-gyre gyre (IGG).
Inter-gyre gyre: consistent with the barotropic streamfunction anomaly driven by NAO wind-curl as predicted by Sverdrup balance:

29. NAO/Ocean Circulation Interactions
SST Composite maps keyed to the SST PC1. (Years with PC1 > 1 std minus years with PC1 < -1 std for different time-shifts). Note the re-emergence of the tripole after 5 yr.
This advective mechanism increases the long term memory of the SST,
and the re-emergence of the SST tripole, on multiannual time-scales.

30. Lead-lag Correlation Analysis of NAOI vs SST anomaly
(NAOI leading for positive time lags)

31. The role of ocean circulation in the meridional heat transport.
Gyre circulation
Meridional overturning circulation
c.i. : 10 Sv.

32. (51N). [NAOI leads for positive lags.]
NAOI/Meridional Heat Transport lagged correlation at the cross-gyre boundary
(51N). [NAOI leads for positive lags.]
Gyre
Ovt
Total
time lag
Correlation is larger for the gyre contribution. Max. correlation for both ovt
and gyre is achieved in 1-2 yrs and is positive. Hence, NAO+ drives a
delayed poleward heat transport which concurs to a warming of the SPG.
A warming in the subpolar region pushes the NAO towards a negative phase (NAO-)
which in turn produces a weaker northward heat transport, restoring cooler conditions
at the northern latitudes.