Presentation on theme: "S. Gualdi, A. Bellucci, R. Mathew, E. Scoccimarro"— Presentation transcript:
1S. Gualdi, A. Bellucci, R. Mathew, E. Scoccimarro INGVISTITUTO NAZIONALE diGEOFISICA e VULCANOLOGIAClimate variability and change in the Euro-Mediterranean region as simulated with a global climate modelS. Gualdi, A. Bellucci, R. Mathew, E. ScoccimarroINGV-CMCC
2OBJECTIVE & MOTIVATION Regional climate changes can differ substantially from the global changeprojection and the assessment of the regional patterns of climate changeis one of the principal goal of the research activityRegional 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 fromlow-resolution coupled model scenarios (no feedbacks)Recent (IPCC) climate scenario simulations performed with high-resolutionglobal CGCMs (e.g., GFDL, INGV and MIROC) allow some detailedanalyses of the regional patterns of climate change including (in principle)all the feedback processes
4OBJECTIVE & MOTIVATION Main features of the regional (Euro-Mediterranean) patternsof climate change produced with a global, high-resolution,state of the art coupled model will be discussedImplications for the next challenges that will be faced in thefield of climate change simulations: short-term projections(multi-decadal climate prediction experiments)DATAObservations: ERA-40 re-analyses ( ),CMAP (Xie-Arkin) precipitation ( )Simulations: IPCC scenarios: 20th Century ( ), A2 ( )data available at the PCMDI archive (www.pcmdi-llnl.gov)
5INGV-CMCC COUPLED MODEL SINTEX-G (SXG) Gualdi et al. 2006Gualdi et al. 2008Bellucci et al. 2008ECHAM-4.6:Max-Planck-Inst. HamburgGlobal, T106 resolution (1.1ºx1.1º)19 Vertical levelsAtmosphereCouplerOcean&Sea-IceOASIS 2.4Coupling every 1.5 hoursNo Flux AdjustmentOPA 8.2:LODYC, Paris,Global, Resol -> 2º longitude0.5º - 2º latitude31 Vertical LevelsLim:UCL, Louvain-la-Neuve,3-layer modelDyn & Thermodyn
620th Century EURO-MEDITERRANEAN Precipitation 2m-Temperature ObservationsModelObservationsModelJFMAMJJASONDmm/day°CPrecipitation2m-Temperature
9SUMMARY 1The Euro-Med region undergoes a substantial warming in allseason. Warming is maximum over the north-east Europe inwinter and south-western Europe-Mediterranean in summerIn summer precipitation decreases over most of the Euro-Med. In winter it increases over north Europe and decreasesover south Europe and the MediterraneanThese results are fully consistent with the results obtainedwith several other CGCMs (IPCC-AR4)
10Implications for the short-term climate projections (multi-decadal climate prediction experiments)Similarities between the regional patterns of climate change and the variabilityassociated with the NAOPrecipitationA2( ) – 20C( ) JFMNAO +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?
11According to a simple interpretation (climate noise paradigm) the relevant space-time scales of NAO are determined by processes which are internal to the atmosphereNAO -NAO +
12Among 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 activityPower spectrum of Z300 PC1(Feldstein, 2000)red noiseAmong the external forcings which may potentially affect the NAOvariability what is the role of the ocean?
13NAO and North Atlantic variability SXG 20CNAO and North Atlantic variability(Bellucci et al. 2008)SXG SLP EOF1 (34%)Power SpectraSXG SST TripoleOBS NAOISXG NAOISXG SST EOF1 (30%)SST PC1
14SST 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.
15200-hPa Z and SST Composite maps (keyed to the SST PC1)GPH c.i.: 5 m
16The NAO forces a gyre circulation anomaly which enhances the inter-gyre gyre transfer of SST anomaliesComposite 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:
17SST/NAO interaction occurs through anomalous wind-driven circulation consistent with Marshall et al. (2001) paradigm for mid-latitude coupled variabilityDuring a NAO+ phase the IGG contributes to the warming of high latitudes, hence weakening the SST meridional gradientwindIGG-Subtropical/subpolargyre boundaryNAO +sst+Once the northern SST dipole has reversed its sign, there are favourable conditionsfor the NAO to enter into a negative phasewindIGG+NAO -Subtropical/subpolargyre boundary-sst
18Results from a CGCM suggest that midlatitude variability in SUMMARY 2Results 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)These results are qualitatively consistent with the delayed-oscillator paradigm of a coupled mode of variability of theNorth 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
28The 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:
29NAO/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.
30Lead-lag Correlation Analysis of NAOI vs SST anomaly (NAOI leading for positive time lags)
31The role of ocean circulation in the meridional heat transport. Gyre circulationMeridional overturning circulationc.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.]GyreOvtTotaltime lagCorrelation is larger for the gyre contribution. Max. correlation for both ovtand gyre is achieved in 1-2 yrs and is positive. Hence, NAO+ drives adelayed 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.