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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. - PowerPoint PPT Presentation
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Bruegel : The Harvesters (1565)
Mechanisms for European summer
temperature response to solar
forcing over the last millenniumSwingedouw D., Terray L., Servonnat J., Guiot J.
Background IPCC 2007: large increase in temp.
and drought in the Med. region, while increase in precip. in Northern Europe
« Transition zone » governed by evapotranspiration (Boé and Terray 2008)
Evapotranspiration was also playing a crucial role in 2003 heat wave (Fischer et a. 2007)
Transition zone
IPCC 2007, Chap. 11, Fig. 2
Last millennium: a case-test for European summer response to
radiative changes?
A recent reconstruction now available (Guiot et al. 2010) goes back to 600
Use lots of pollen data which allow a better representation of low frequency
Use of this dataset to test a climate model response to solar forcing
Climate simulation with complex land-surface scheme: CNRM-CM3 using SECHIBA (Swingedouw et al. 2011)
Solar, GHG and volcanic forcings
Last millennium simulation
Solar forcing fingerprints
Low but significant correlation with solar forcing
both in data and model
Summer European temperature
Regression over solar variations : 90%: 95%: 99%
Solar forcing impact in the model
Schar et al. 1999
Large-scale response
Sea ice is responding to solar changes by decreasing its cover in the Nordic Seas
The large-scale atmospheric circulation does not exhibit significant changes over the North Atlantic sector in summer
Surface radiative changes in the model
Evapotranspiration driver
Evapotranspiration over Central Europe is highly correlated in summer with water content in the soil
It is therefore the loading in water of the soil in winter that is mainly driving changes in evapotranspiration
Indeed winter precipitation slighty increases with solar forcing due to Clausius-Clapeyron relationship (not shown)
1950-2006 (Alkama et al. 2010)
Summary of the mechanism
Loading of soil water reservoir in winter
Evapotranspiration increases in summer
More evaporation in the tropics
Summary of the mechanism
55°N25°N 75°N
Summary of the mechanism
55°N25°N 75°N
Temperature
Conclusions Solar forcing over last millennium has small but significant
inprints over Europe in summer with similar latitudinal pattern in reconstruction and model
Long time scales useful to increase signal to noise ratio Evapotranspiration responds strongly to solar forcing in
Central Europe and damps temperature signal through cloud feedback
Sea-ice also responds strongly and enhances solar forcing signal in Northern Europe
Too large amplitude of TSI variations in CNRM-CM3 simulation?
Thank you!
Swingedouw D., Terray L., Servonnat J., Guiot J. Mechanisms for European summer temperature response to solar forcing over the last
millennium. Climate of the past 8, 1487-1495, 2012
TSI
Winter precipitation
Early spring soil moisture
Summer Evapotranspiration
Convective clouds
Surface SW
Surface temperature
Convective precipitation
Non convective precipitationSoil
moisture+
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Schär et al. (1999) positive feedback
loop
Mechanisms to explain Central Europe response to solar forcing
