Impact of different estimations of the background-error covariance matrix on climate reconstructions based on data assimilation

Valler, Veronika; Franke, Jörg; Brönnimann, Stefan (2018). Impact of different estimations of the background-error covariance matrix on climate reconstructions based on data assimilation. Climate of the past discussions, pp. 1-27. Copernicus Publications 10.5194/cp-2018-168

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Data assimilation has been adapted in paleoclimatology to reconstruct past climate states. A key component of the assimilation system is the background-error covariance matrix, which controls how the information from observations spreads into the model space. In ensemble-based approaches, the background-error covariance matrix can be estimated from the ensemble. Due to the usually limited ensemble size, the background-error covariance matrix is subject to the so-called sampling error. We test different methods to reduce the effect of sampling error in a published paleo data assimilation setup. For this purpose, we conduct a set of experiments, where we assimilate early instrumental data and proxy records stored in trees, to investigate the effect of 1) the applied localization function and localization length scale; 2) multiplicative and additive inflation techniques; 3) temporal localization of monthly data, which applies if several time steps are estimated together in the same assimilation window. We find that the estimation of the background-error covariance matrix can be improved by additive inflation where the background-error covariance matrix is not only calculated from the sample covariance, but blended with a climatological covariance matrix. Implementing a temporal localization for monthly resolved data also led to a better reconstruction.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geography > Physical Geography > Unit Climatology
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography
08 Faculty of Science > Institute of Geography > Physical Geography

UniBE Contributor:

Valler, Veronika; Franke, Jörg and Brönnimann, Stefan

Subjects:

300 Social sciences, sociology & anthropology
500 Science > 550 Earth sciences & geology
900 History > 910 Geography & travel

ISSN:

1814-9359

Publisher:

Copernicus Publications

Language:

English

Submitter:

Saba Sabina Baer

Date Deposited:

22 Mar 2019 14:37

Last Modified:

22 Mar 2019 14:37

Publisher DOI:

10.5194/cp-2018-168

BORIS DOI:

10.7892/boris.128067

URI:

https://boris.unibe.ch/id/eprint/128067

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