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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 4
Clim. Past, 13, 379–393, 2017
https://doi.org/10.5194/cp-13-379-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Clim. Past, 13, 379–393, 2017
https://doi.org/10.5194/cp-13-379-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Apr 2017

Research article | 20 Apr 2017

Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction

Atsushi Okazaki1 and Kei Yoshimura2 Atsushi Okazaki and Kei Yoshimura
  • 1RIKEN Advanced Institute for Computational Science, Kobe, Japan
  • 2Institute of Industrial Science, The University of Tokyo, Tokyo, Japan

Abstract. Data assimilation (DA) has been successfully applied in the field of paleoclimatology to reconstruct past climate. However, data reconstructed from proxies have been assimilated, as opposed to the actual proxy values. This prevented full utilization of the information recorded in the proxies.

This study examined the feasibility of proxy DA for paleoclimate reconstruction. Isotopic proxies (δ18O in ice cores, corals, and tree-ring cellulose) were assimilated into models: an isotope-enabled general circulation model (GCM) and forward proxy models, using offline data assimilation.

First, we examined the feasibility using an observation system simulation experiment (OSSE). The analysis showed a significant improvement compared with the first guess in the reproducibility of isotope ratios in the proxies, as well as the temperature and precipitation fields, when only the isotopic information was assimilated. The reconstruction skill for temperature and precipitation was especially high at low latitudes. This is due to the fact that isotopic proxies are strongly influenced by temperature and/or precipitation at low latitudes, which, in turn, are modulated by the El Niño–Southern Oscillation (ENSO) on interannual timescales.

Subsequently, the proxy DA was conducted with real proxy data. The reconstruction skill was decreased compared to the OSSE. In particular, the decrease was significant over the Indian Ocean, eastern Pacific, and the Atlantic Ocean where the reproducibility of the proxy model was lower. By changing the experimental design in a stepwise manner, the decreased skill was suggested to be attributable to the misrepresentation of the atmospheric and proxy models and/or the quality of the observations. Although there remains a lot to improve proxy DA, the result adequately showed that proxy DA is feasible enough to reconstruct past climate.

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Short summary
Data assimilation has been successfully applied in the field of paleoclimatology to reconstruct past climate. However, data reconstructed from proxies have been assimilated, as opposed to the actual proxy values, which prevented full utilization of the information recorded in the proxies. This study propose a new data assimilation system in which actual proxy data are directly assimilated.
Data assimilation has been successfully applied in the field of paleoclimatology to reconstruct...
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