Clim. Past Discuss., 9, 3953-3991, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Investigating the consistency between proxies and between proxies and models using data assimilation: a mid-Holocene case study
A. Mairesse1, H. Goosse1, P. Mathiot1,*, H. Wanner2, and S. Dubinkina1
1Université catholique de Louvain, Earth and Life Institute, Georges Lemaître Centre for Earth and Climate Research, Place Louis Pasteur, 3, 1348 Louvain-la-Neuve, Belgium
2Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
*now at: British Antarctic Survey, Natural Environment Research Council, Cambridge, UK

Abstract. The mid-Holocene (6 thousand years before present) is a key period to study the consistency between model results and proxy data as it corresponds to a standard test for models and a reasonable number of proxy records are available. Taking advantage of this relatively large amount of information, we have first compared a compilation of 50 air and sea surface temperature reconstructions with the results of three simulations performed with general circulation models and one carried out with LOVECLIM, a model of intermediate complexity. The conclusions derived from this analysis confirm that models and data agree on the large-scale spatial pattern but underestimate the magnitude of some observed changes and that large discrepancies are observed at the local scale. To further investigate the origin of those inconsistencies, we have constrained LOVECLIM to follow the signal recorded by the proxies selected in the compilation using a data assimilation method based on a particle filter. In one simulation, all the 50 proxies are used while in the other two, only the continental or oceanic proxies constrains the model results. This assimilation improves the consistency between model results and the reconstructions. In particular, this is achieved in a robust way in all the experiments through a strengthening of the westerlies at mid-latitude that warms up the Northern Europe. Furthermore, the comparison of the LOVECLIM simulations with and without data assimilation has also objectively identified 16 proxies whose reconstructed signal is either incompatible with the one recorded by some other proxies or with model physics.

Citation: Mairesse, A., Goosse, H., Mathiot, P., Wanner, H., and Dubinkina, S.: Investigating the consistency between proxies and between proxies and models using data assimilation: a mid-Holocene case study, Clim. Past Discuss., 9, 3953-3991, doi:10.5194/cpd-9-3953-2013, 2013.
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