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Bruegel : The Harvesters (1565 )

Mechanisms for European summer temperature response to solar forcing over the last millennium Swingedouw D., Terray L., Servonnat J., Guiot J. . Bruegel : The Harvesters (1565 ). Background.

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Bruegel : The Harvesters (1565 )

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  1. Mechanisms for European summer temperature response to solar forcing over the last millennium Swingedouw D., Terray L., Servonnat J., Guiot J. Bruegel : The Harvesters (1565)

  2. Background • IPCC 2007: large increase in temp. and drought in the Med. region, whileincrease in precip. in Northern Europe • « Transition zone » governed by evapotranspiration (Boé and Terray 2008) • Evapotranspirationwasalsoplaying a crucial role in 2003 heatwave (Fischer et a. 2007) Transition zone IPCC 2007, Chap. 11, Fig. 2

  3. Last millennium: a case-test for Europeansummerresponse to radiative changes? • A recent reconstruction nowavailable (Guiot et al. 2010)goes back to 600 • Use lots of pollen data whichallow a betterrepresentation of lowfrequency • Use of thisdataset to test a climate model response to solar forcing

  4. Last millennium simulation • Climate simulation withcomplex land-surface scheme: CNRM-CM3 using SECHIBA (Swingedouw et al. 2011) • Solar, GHG and volcanic forcings • Influence du forçage solaire et volcanique

  5. Regression over solar variations : 90% Solar forcing fingerprints : 95% : 99% Low but significantcorrelationwithsolar forcing both in data and model SummerEuropeantemperature

  6. Solar forcing impact in the model Schar et al. 1999

  7. Large-scaleresponse • Seaiceisresponding to solar changes by decreasingitscover in the NordicSeas • The large-scaleatmospheric circulation does not exhibitsignificant changes over the North Atlantic sector in summer

  8. Surface radiative changes in the model

  9. Evapotranspiration driver 1950-2006 (Alkama et al. 2010) • Evapotranspiration over Central Europe ishighlycorrelated in summerwith water content in the soil • It istherefore the loading in water of the soil in winterthatismainlydriving changes in evapotranspiration • Indeedwinterprecipitationslightyincreaseswithsolar forcing due to Clausius-Clapeyron relationship (not shown)

  10. Summary of the mechanism Mettre un nuage avec pluie pour hiver Utiliser tableau Bruegel pour illustrer hiver et ete… More evaporation in the tropics Evapotranspiration increases in summer Loading of soil water reservoir in winter

  11. Summary of the mechanism 25°N 75°N 55°N

  12. Summary of the mechanism Temperature 25°N 75°N 55°N

  13. Conclusions • Solar forcing over last millennium has small but significantinprints over Europe in summerwithsimilar latitudinal pattern in reconstruction and model • Long time scalesuseful to increase signal to noise ratio • Evapotranspiration respondsstrongly to solar forcing in Central Europe and dampstemperature signal throughcloud feedback • Sea-icealsorespondsstrongly and enhancessolar forcing signal in Northern Europe • Too large amplitude of TSI variations in CNRM-CM3 simulation?

  14. Thankyou! Swingedouw D., Terray L., Servonnat J., Guiot J. Mechanismsfor Europeansummertemperatureresponse to solar forcing over the last millennium. Climateof the past 8, 1487-1495, 2012 Didier.Swingedouw@lsce.ipsl.fr

  15. Mechanisms to explain Central Europe response to solar forcing TSI + + Winter precipitation + Earlyspringsoilmoisture + Non convective precipitation + + Summer Evapotranspiration Soilmoisture + + Convective precipitation Convective clouds + - Surface SW Schär et al. (1999) positive feedback loop + Surface temperature

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