Climate variability and change in the Euro-Mediterranean region as simulated with a global climate model S. Gualdi, A. Bellucci, R. Mathew, E. Scoccimarro.

Climate variability and change in the Euro-Mediterranean region as simulated

with a global climate model

S. Gualdi, A. Bellucci, R. Mathew, E. ScoccimarroINGV-CMCC

INGV ISTITUTO NAZIONALE di

GEOFISICA e VULCANOLOGIA

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

horizontal resolution ~250/300 Km IPCC-AR4 standard

horizontal resolution ~ 120Km INGV-IPCC runs

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 (1958-2001), CMAP (Xie-Arkin) precipitation (1979-2001)

Simulations: IPCC scenarios: 20th Century (1951-2000), A2 (2001-2100) data available at the PCMDI archive (www.pcmdi-llnl.gov)

INGV-CMCC COUPLED MODEL SINTEX-G (SXG)

OPA 8.2:LODYC, Paris,Global, Resol -> 2º longitude

0.5º - 2º latitude31 Vertical Levels

Lim:UCL, Louvain-la-Neuve,3-layer modelDyn & Thermodyn

ECHAM-4.6: Max-Planck-Inst. Hamburg Global, T106 resolution (1.1ºx1.1º)19 Vertical levels

Atmosphere

Coupler

Ocean&

Sea-Ice

OASIS 2.4Coupling every 1.5 hours

No Flux Adjustment

Gualdi et al. 2006Gualdi et al. 2008Bellucci et al. 2008

EURO-MEDITERRANEAN

Observations Model

mm/day

JFM

AMJ

JAS

OND

20th Century

Observations Model

Precipitation 2m-Temperature°C

SCENARIO: A2 – 20C 2m-Temperature

A2(2001-2050) – 20C(1951-2000) JFM

A2(2001-2050) – 20C(1951-2000) JAS

A2(2051-2100) – 20C(1951-2000) JFM

A2(2051-2100) – 20C(1951-2000) JAS

°C

A2(2001-2050) – 20C(1951-2000) JFM

A2(2001-2050) – 20C(1951-2000) JAS

A2(2051-2100) – 20C(1951-2000) JFM

A2(2051-2100) – 20C(1951-2000) JAS

SCENARIO: A2 – 20C precipitation

mm/day

SUMMARY 1

These results are fully consistent with the results obtained with several other CGCMs (IPCC-AR4)

In summer precipitation decreases over most of the Euro-Med. In winter it increases over north Europe and decreasesover south Europe and the Mediterranean

The Euro-Med region undergoes a substantial warming in allseason. Warming is maximum over the north-east Europe inwinter and south-western Europe-Mediterranean in summer

NAO +

Precipitation A2(2051-2100) – 20C(1951-2000) JFM

Implications for the short-term climate projections (multi-decadalclimate prediction experiments)

Similarities between the regional patterns of climate change and the variabilityassociated with the NAO

To which extent can we discriminate between the climate changesignal and the anomalies induced by the natural variability (NAO)in the short-term climate prediction experiments?

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 -

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

red noise

Power spectrum of Z300 PC1(Feldstein, 2000)

Among the external forcings which may potentially affect the NAOvariability what is the role of the ocean?

SXG SLP EOF1 (34%)

OBS NAOI

SXG NAOI

SXG SST Tripole

Power Spectra

SXG SST EOF1 (30%) SST PC1

SXG 20C NAO and North Atlantic variability (Bellucci et al. 2008)

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.

SST Composite maps (keyed to the SST PC1)

GPH c.i.: 5 m

200-hPa Z and SST Composite maps(keyed to the SST PC1)

Inter-gyre gyre: consistent with the barotropic streamfunction anomaly driven by NAO wind-curl as predicted by Sverdrup balance:

The NAO forces a gyre circulation anomaly which enhances the inter-gyre gyre transfer of SST anomalies

(x,)a tan

0k(

f)dx '

xE

x

Composite of JFM wind stress: NAO+ minus NAO- Ψ EOF1:Inter-gyre gyre (IGG)

+

-

wind

IGG

sst

During a NAO+ phase the IGG contributes to the warming of high latitudes, hence weakening the SST meridional gradient

NAO +

Once the northern SST dipole has reversed its sign, there are favourable conditionsfor the NAO to enter into a negative phase

-

+

wind

IGG

sstNAO -

Subtropical/subpolar gyre boundary

Subtropical/subpolar gyre boundary

SST/NAO interaction occurs through anomalous wind-driven circulation consistentwith Marshall et al. (2001) paradigm for mid-latitude coupled variability

Results from a CGCM suggest that midlatitude variability inthe North Atlantic on multi-annual time-scales is determinedby an oscillatory mode involving co-varying changes in SSTand atmospheric circulation with a typical NAO-like pattern(Bellucci et al. 2008)

SUMMARY 2

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 ofvariability active at multi-annual time-scales would be ofgreat importance for the study of climate variability andclimate change in the Euro-Mediterranean region and,more generally, of relevance for the feasibility short-termclimate projection experiments

Thanks!

THE SCENARIO SIMULATIONS

global mean surface temperature anomaly

Observations

SST

SST

Precip

Precip

JJASOMEAN

DJFMAMEAN

MODEL PERFORMANCE: GLOBAL

Model

20th Century

STANDARD DEVIATION 2m-Temperature

°CSXG A2 (2001-2050) SXG A2 (2051-2100)

OBSERVATIONS (1958-2001) SXG 20C (1951-2000)

JFM

°C

STANDARD DEVIATION 2m-Temperature

°C

SXG A2 (2001-2050) SXG A2 (2051-2100)

OBSERVATIONS (1958-2001) SXG 20C (1951-2000)

JAS

TELECONNECTIONS: NAO

anomaly regression NAO index JFMOBS

°C mm/day

TELECONNECTIONS: NAO

anomaly regression NAO indexSXG 20C

°C mm/day

JFM

TELECONNECTIONS: NAO

anomaly regression NAO index JFMSXG A2

°C mm/day

Year 0

Year +1

Year +2

Year +3

Sutton and Allen, 1997

Year 0

Year 1

Year 2

Year 3

SINTEX-G

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:

The anomalous gyre circulation response to the NAO wind-stress

Composite of JFM wind stress :NAO+ minus NAO-

x

xE

dxf

ax ')(

tan),(

0

k

This advective mechanism increases the long term memory of the SST,and the re-emergence of the SST tripole, on multiannual time-scales.

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.

NAO/Ocean Circulation Interactions

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

Gyre circulation Meridional overturning circulation

c.i. : 10 Sv.

The role of ocean circulation in the meridional heat transport.

Correlation is larger for the gyre contribution. Max. correlation for both ovtand 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 conditionsat the northern latitudes.

GyreOvtTotal

time lag

NAOI/Meridional Heat Transport lagged correlation at the cross-gyre boundary (51N). [NAOI leads for positive lags.]