GKS!S 99/E/54 Climate simulations for the last interglacial period by means of climate models of different complexity Worn Fachbereich Geowissenschaften der Universitat Hamburg als Dissertation angenommene Arbeit) Authoress: M. L. Montoya (Meteorological Institute, University Hamburg, and as a guest in the GKSS Research Centre, Inst. of Hydrophysics) GKSS-Forschungszentrum Geesthacht GmbH ● Geesthacht ● 1999 Address: MariaLuisaMontoya PotsdamInstitutefor ClimateImpactResearch(PIK) PO BOX601203 14412Potsdam,Germany Phone:+49-331-288-2566 Die extemenBerichtederGKSSwerdenkostenlosabgegeben. The delivery of the externalGKSS reportsis free of charge, Anforderungen/ltequests: GKSS-ForschungszentrumGeesthachtGmbH Bibliothek/Library Postfach 1160 D-2 1494 Geesthacht Germany Fax.:(49)04152/871717 Als Manuscriptvervielfaltigt. FiirdiesenBerichtbehaltenwir unsalleRechtevor. GKSS-ForschungszentrumGeesthachtGmbH - Telefon (04152 )87-O Max-Planck-Stra13e”D-21502Geesthacht/Postfach1160”D-21494Geesthacht DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. mm!!!!! GKSS 99/E/54 Climate simulations for the last interglacial period by means of climate models of different complexity (Vom Fachbereich Geowissenschaften der UniversitatHamburg als Dissertation angenomnzeneA,rbeit) M. L. Montoya 128 pages with 57~gures and 9 tables Abstract Climatic conditions during the last interglacial(125,000 years before present) are investigated with two climatemodels of differentcomplexity: the atmosphere-oceangeneralcirculationmodel ECHAM-l/LSG and the climate system model of intermediatecomplexity CLIMBER-2. In par- ticularthe role of vegetationat the lastinterglacialmaximum, and its importancefor a consistent simulation of the Mid-Holocene climate, has been investigated (EU project ASPEN: Air-Sea Wave Processes in Climate Change Models). Comparisonof theresultsof thetwo modelsreveals a broad agreementin most large-scalefeatures.Nevertheless,discrepanciesare also detected.Es- sentiaIIy,the models differ in their ocean circulationresponses. Profiting of the fast turnaround timeof CLIMBER-2, a number of sensitivityexperimentshave been performed to try to explain the possible reasons for these differences, and to analyze additionaleffects not included in the previoussimulations.Inparticular,therole of vegetationatthe lastinterglacialmaximumhasbeen investigated.Comparison of the simulated responses against CLIMAP reconstructed SS’TSfor Marine Isotope Stage 5e shows a satisfactory agreementwithin the data uncertainties. Klimasimulationen fiir die letzte interglaziale Periode anhand von Klimamodellen unterschiedlicher Komplexitat Zusammenfassung Die klimatischenBedingungenwahrendder letzten interglazialenPeriode (vor 125000 Jahren) werden anhand zweier Klimamodelle unterschiedlicher Komplexitat untersucht:dem C)zean- Atmosphare gekoppelten allgemeinen Zirkulatonsmodell ECHAM- l/LSG und dem K.lima- systemmodell mittlererKomplexitat CLIMBER-2. Insbesonderewurde die Rolle derVegetation in der letzten interglazialen Periode und ihre Bedeutung fir eine konsistente Simulation des mittelholozaenischenKlimas untersucht(EU-ProjektASPEN: Air-SeaWave Processes in Climate ChangeModels – ,,Klimavariationenin historischenZeiten”). Der Vergleich der Ergebnissebei- der Modelle zeigt eine gute Ubereinstimmung der meisten der grofiskaligen Eigensch.aften, allerdings zeigen sich such Unterschiede. Die Modellergebnisse unterscheidensich im wesent- Iichen in der Antvvortder Ozeanischen Zirkulation. Die kurze Rechenzeit von CLIMBER-2 ermoglicht eine nahereUntersuchungdieserUnterschiedeund zusatzlicherAntriebsfaktoren,die in den bisherigenSimulationennichtbetrachtetwurden.Insbesonderewurde die Rolle der Vege- tationin der letzteninterglazialenPeriode untersucht.Der Vergleich der simuliertenAntworten mit den von CLIMAP rekonstruiertenOzeanoberflachentemperaturenzeigen eine befriedigende Ubereinstimmunginnerhalbder Ungewifiheit der Daten. Manuscriptreceived/Manuskripteinganginder Redaktion:4. Oktober 1999 Contents Contents i Glossary v List of Figures vii ... List of Tables X111 1 Introduction 1 1.1 Climate models for the study of paleoclimates . 1 2 The geological evidence for the LIG 7 2.1 The definition of the LIG in the terrestrial and marine records. Chronology. 7 2.2 Reconstructions on regional to global scales . 9 2.2.1 The CLIMAP SST reconstruction for MIS 5e . 9 2.2.2 LIGA 1991 . 10 2.2.3 The Last Interglacial in northwestern Europe . 10 2.3 Evidence on the deep ocean circulation . 12 2.4 Theice core record . 12 2.5 The Monsoon atthe LAG . 14 3 The experimental set-up 15 3.1 The ECHAM-1/LSG climate model . 15 3.1.1 The atmospheric component . 15 3.1.2 The oceanic component . 16 3.1.3 The coupling . 17 3.2 The control run. .o. o.... .. O.... 17 3.3 The external forcing .. o.... .O. o . ..e . .. a.. .OO. 19 i ii CONTENTS 3.3.1 The definition of the seasons . 19 3.3.2 Changes in incoming solar radiation . 21 4 Results with the ECHAM-1/LSG coupled GCM 23 4.1 Temporal evolution . 23 4.2 Large-scale atmospheric patterns . 24 4.2.1 Northern summer . 27 4.2.2 Northern winter . 33 4.2.3 Armual mean . 34 4.3 Ocean circulation . 37 4.4 Climate variability . 42 4.4.1 Atmospheric variability: synoptic scale disturbances . 44 4.4.20 cean variability . 45 4.5 Summary. 48 5 Results with the CLHV!!BER-2 climate system model 51 5.1 The CLIMBER-2 climate system model . 52 5.2 Experimental set-up . 53 5.3 Temporal evolution . 53 5.4 Comparison of mean simulated fields . 54 5.4.1 Near surface temperature . 55 5.4.2 Precipitation . 55 5.4.3 Atmospheric Circulation . 59 5.4.4 Mean ocean circulation . 60 5.5 Sensitivity experiments . 61 5.5.1 Prescribed freshwater flux run . 62 5.5.2 Radiative forcing . 63 5.5.3 The role of interactive vegetation . 66 5.6 Feedback Analysis . .. 71 5.7 Summary . .. 77 6 Comparison against reconstructed SSTS 81 6.1 CLIMAP SSTS . 81 6.2 Model-data intercornparison . 82 6.3 Global temperature differences Erompresent . 84 6.4 Summary . .. 86 7 Conclusions and Discussion 89 7.1 ECHAM-1/LSG . < . 90 7.2 CLIMBER-2 . < . 92 7.3 Model-data intercornparison . 94 7.40utlook . .. 95 8 Acknowledgments 97 9 Appendix 99 ... CONTENTS m References 115 Glossary AABW: Antarctic Bottom Water. AET: Actual Evapotranspiration. AGCM: Atmospheric General Circulation Model. A: Atmosphere. AO: Atmosphere-Ocean. AOV: Atmosphere-Ocean-Vegetation. BATS: Biosphere-Atmosphere Transfer Scheme. CLIMAP: Climate Long Range Investigation and Mapping Project. CLIMBER: Climate and Biosphere. DJF: December-January-February. EBM: Energy Balance Model. ECHAM: European Centre and Hamburg. ECMWF: European Centre for Medium Range Weather Forecasts. EOF: Empirical Orthogonal Function. GCM: General Circulation Model. GDD: Growing Degree Days. GIN: Greenland-Iceland-Norwegian. GISP2: Greenland Ice Sheet Project. GRIP: Greenland Ice Core Project. IRD: Ice Rafted Debris. v vi GLOSARIO JJA: June-JuIy-August. KYR Thousand years ago. K131?: Thousand years Before Present. LGM: Last Glacial Maximum. LIG: Last Interglacial. LIGA GROUP: Working group for the study of the Last Interglacial in the Arctic and sub-Arctic. LS~: Large Scale Geostrophic. MIS: Marine Isotope Stage. MTC O: Mean Temperature of the Coldest Month. NADW: North Atlantic Deep Water. OGCM: Ocean General Circulation Model. PIK: Potsdam Institute for Climate Impact Research. P-E: precipitation minus evaporation. PPMV: parts per million (in volume). SLP: sea Level Pressure. SS S: Sea Surface Salinity. SST: Sea Surface Temperature. THC: Thermohaline circulation. VEC ODE: Vegetation Continuous Description Model. List of Figures 3.1 The ECHAM-1 model orography (m) in T21 resolution and the model continents . ...16 3.2 Time vs. latitude (top) and celestial longitude vs. latitude (bottom) differences in zonally averaged incoming solar radiation at the top of the atmosphere (125,000 years ago minus present, Win-2). 20 3.3 Position of the solstices and equinoxes a) for the control run (the present), and b) the Eemian run (125,000 years ago). Dates of solstices and equinoxes are given in parenthesis. VE: Vernal equinox, AE: Autum-- nal Equinox, SS: Summer solstice, WS: Winter Solstice. 21 3.4 Difference in zonally averaged mean insolation in JJA (dotted line), DJF (dashed line) and in the annual mean (solid line) (Win-2). 22 4.1 Time series of the mean annual a) total sea ice extent (m2), b) total sea ice volume (m3), in the Northern (solid line) and Southern Hemisphere (dashed line), and c) globally averaged near-surface (2 m) temperature (°C), for the control (thin line) and Eemian run (thick line). 24 4.2 Time series of the mean annual globally averaged temperature of the ocean at a) 75 m, b) 250 m, c) 1000 m, d) 2000 m, and e) 4000 m depth for the control (dashed line) and Eemian run (solid line) (“C). Note that the vertical scale is the same for all levels. 25 4.3 Time series of the mean annual globally averaged salinity of the ocean at a) 75 m, b) 250 m, c) 1000 m, d) 2000 m and e) 4000 m depth for the control (dashed line) and Eemian run (solid line) (psu). Note that the vertical scale is the same for all levels. 25 vii ... Vlll LIST OF FIGURES 4.4 Time series of a) mass transport of the Antarctic Circumpolar Current (ACC) across the Drake passage, b) outflow of North Atlantic Deep Water (NADW) at 30°S, and c) amplitude of the Atlantic overturning circulation, defied as the maximum value of the zonally averaged mass transport strearnfunction of the meridional overturning