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

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

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) 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

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

SCENARIO: A2 – 20C 2m-Temperature A2(2001-2050) – 20C(1951-2000) JFM A2(2051-2100) – 20C(1951-2000) JFM A2(2001-2050) – 20C(1951-2000) JAS A2(2051-2100) – 20C(1951-2000) JAS °C

SCENARIO: A2 – 20C precipitation A2(2001-2050) – 20C(1951-2000) JFM A2(2051-2100) – 20C(1951-2000) JFM A2(2001-2050) – 20C(1951-2000) JAS A2(2051-2100) – 20C(1951-2000) JAS mm/day

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)

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(2051-2100) – 20C(1951-2000) 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?

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 +

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?

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

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.

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

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:

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

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

Thanks!

THE SCENARIO SIMULATIONS global mean surface temperature anomaly

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

JFM STANDARD DEVIATION 2m-Temperature OBSERVATIONS (1958-2001) SXG 20C (1951-2000) °C SXG A2 (2001-2050) SXG A2 (2051-2100) °C

JAS STANDARD DEVIATION 2m-Temperature OBSERVATIONS (1958-2001) SXG 20C (1951-2000) SXG A2 (2001-2050) SXG A2 (2051-2100) °C

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

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

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

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

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:

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.

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

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

(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.