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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-137
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-137
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Dec 2019

Submitted as: research article | 04 Dec 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Assimilating monthly precipitation data in a paleoclimate data assimilation framework

Veronika Valler1,2, Yuri Brugnara1,2, Jörg Franke1,2, and Stefan Brönnimann1,2 Veronika Valler et al.
  • 1Institute of Geography, University of Bern, Bern, Switzerland
  • 2Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Abstract. Data assimilation approaches such as the ensemble Kalman filter method have become an important technique for paleoclimatological reconstructions and reanalysis. Different sources of information from proxy records and documentary data to instrumental measurements were assimilated in previous studies to reconstruct past climate fields. However, precipitation reconstructions are often based on indirect sources (e.g., proxy records). Assimilating precipitation measurements is a challenging task because they have high uncertainties, often represent only a small region and generally do not follow Gaussian distribution. In this paper, a set of experiments are conducted to test the possibility of using information about precipitation in climate reconstruction with monthly resolution by assimilating monthly instrumental precipitation amounts or the number of wet days per month, solely or in addition to other climate variables such as temperature and sea level pressure, into an ensemble of climate model simulations. The skill of all variables (temperature, precipitation, sea-level pressure) improved over the pure model simulations when only monthly precipitation amounts were assimilated. Assimilating the number of wet days resulted in similar or better skill compared to assimilating precipitation amount. The experiments with different types of instrumental observations being assimilated indicate that precipitation data can be useful, particularly if no other variable is available from a given region. Overall the experiments show promising results because with the assimilation of precipitation information a new data source can be exploited for climate reconstructions. Especially the wet day records can become an important data source in future climate reconstructions because many existing records date several centuries back in time and are not limited by the availability of meteorological instruments.

Veronika Valler et al.
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Short summary
Data assimilation is becoming more and more important for past climate reconstructions. The assimilation of monthly resolved precipitation information has not been much explored so far. In this study we analyze the impact of assimilating monthly precipitation amounts and the number of wet day within an existing paleoclimate data assimilation framework. We find increased skill in the reconstruction, suggesting that monthly precipitation can constitute a valuable input for future reconstructions.
Data assimilation is becoming more and more important for past climate reconstructions. The...
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