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| Titel |
On-line and off-line data assimilation in palaeoclimatology: a case study |
| VerfasserIn |
A. Matsikaris, M. Widmann, J. Jungclaus |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 11, no. 1 ; Nr. 11, no. 1 (2015-01-15), S.81-93 |
| Datensatznummer |
250117119
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| Publikation (Nr.) |
 copernicus.org/cp-11-81-2015.pdf |
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| Zusammenfassung |
| Different ensemble-based data assimilation (DA) approaches for palaeoclimate
reconstructions have been recently undertaken, but no systematic comparison
among them has been attempted. We compare an off-line and an on-line
ensemble-based method, with the testing period being the 17th century, which
led into the Maunder Minimum. We use a low-resolution version of Max Planck
Institute for Meteorology Earth System Model (MPI-ESM) to assimilate the Past Global Changes (PAGES) 2k
continental temperature reconstructions. In the off-line approach, the
ensemble for the entire simulation period is generated first and then the
ensemble is used in combination with the empirical information to produce the
analysis. In contrast, in the on-line approach, the ensembles are generated
sequentially for sub-periods based on the analysis of previous sub-periods.
Both schemes perform better than the simulations without DA. The on-line
method would be expected to perform better if the assimilation led to states
of the slow components of the climate system that are close to reality and
the system had sufficient memory to propagate this information forward in
time. In our comparison, which is based on analysing correlations and
differences between the analysis and the proxy-based reconstructions, we find
similar skill for both methods on the continental and hemispheric scales.
This indicates either a lack of control of the slow components in our setup
or a lack of skill in the information propagation on decadal timescales.
Additional experiments are however needed to check whether the conclusions
reached in this particular setup are valid in other cases. Although the
performance of the two schemes is similar and the on-line
method is more difficult to implement, the temporal consistency of the analysis in the
on-line method makes it in general preferable. |
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