Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects
We investigate the initialisation of Northern Hemisphere sea ice in the global climate model ECHAM5/MPI-OM by assimilating sea-ice concentration data. The analysis updates for concentration are given by Newtonian relaxation, and we discuss different ways of specifying the analysis updates for mean t...
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ftdoajarticles:oai:doaj.org/article:9b71cbe2e6474e22bad77abb318987b3 2023-05-15T15:13:36+02:00 Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects S. Tietsche D. Notz J. H. Jungclaus J. Marotzke 2013-01-01T00:00:00Z https://doi.org/10.5194/os-9-19-2013 https://doaj.org/article/9b71cbe2e6474e22bad77abb318987b3 EN eng Copernicus Publications http://www.ocean-sci.net/9/19/2013/os-9-19-2013.pdf https://doaj.org/toc/1812-0784 https://doaj.org/toc/1812-0792 doi:10.5194/os-9-19-2013 1812-0784 1812-0792 https://doaj.org/article/9b71cbe2e6474e22bad77abb318987b3 Ocean Science, Vol 9, Iss 1, Pp 19-36 (2013) Geography. Anthropology. Recreation G Environmental sciences GE1-350 article 2013 ftdoajarticles https://doi.org/10.5194/os-9-19-2013 2022-12-30T22:37:36Z We investigate the initialisation of Northern Hemisphere sea ice in the global climate model ECHAM5/MPI-OM by assimilating sea-ice concentration data. The analysis updates for concentration are given by Newtonian relaxation, and we discuss different ways of specifying the analysis updates for mean thickness. Because the conservation of mean ice thickness or actual ice thickness in the analysis updates leads to poor assimilation performance, we introduce a proportional dependence between concentration and mean thickness analysis updates. Assimilation with these proportional mean-thickness analysis updates leads to good assimilation performance for sea-ice concentration and thickness, both in identical-twin experiments and when assimilating sea-ice observations. The simulation of other Arctic surface fields in the coupled model is, however, not significantly improved by the assimilation. To understand the physical aspects of assimilation errors, we construct a simple prognostic model of the sea-ice thermodynamics, and analyse its response to the assimilation. We find that an adjustment of mean ice thickness in the analysis update is essential to arrive at plausible state estimates. To understand the statistical aspects of assimilation errors, we study the model background error covariance between ice concentration and ice thickness. We find that the spatial structure of covariances is best represented by the proportional mean-thickness analysis updates. Both physical and statistical evidence supports the experimental finding that assimilation with proportional mean-thickness updates outperforms the other two methods considered. The method described here is very simple to implement, and gives results that are sufficiently good to be used for initialising sea ice in a global climate model for seasonal to decadal predictions. Article in Journal/Newspaper Arctic Sea ice Directory of Open Access Journals: DOAJ Articles Arctic Ocean Science 9 1 19 36 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Geography. Anthropology. Recreation G Environmental sciences GE1-350 |
spellingShingle |
Geography. Anthropology. Recreation G Environmental sciences GE1-350 S. Tietsche D. Notz J. H. Jungclaus J. Marotzke Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
topic_facet |
Geography. Anthropology. Recreation G Environmental sciences GE1-350 |
description |
We investigate the initialisation of Northern Hemisphere sea ice in the global climate model ECHAM5/MPI-OM by assimilating sea-ice concentration data. The analysis updates for concentration are given by Newtonian relaxation, and we discuss different ways of specifying the analysis updates for mean thickness. Because the conservation of mean ice thickness or actual ice thickness in the analysis updates leads to poor assimilation performance, we introduce a proportional dependence between concentration and mean thickness analysis updates. Assimilation with these proportional mean-thickness analysis updates leads to good assimilation performance for sea-ice concentration and thickness, both in identical-twin experiments and when assimilating sea-ice observations. The simulation of other Arctic surface fields in the coupled model is, however, not significantly improved by the assimilation. To understand the physical aspects of assimilation errors, we construct a simple prognostic model of the sea-ice thermodynamics, and analyse its response to the assimilation. We find that an adjustment of mean ice thickness in the analysis update is essential to arrive at plausible state estimates. To understand the statistical aspects of assimilation errors, we study the model background error covariance between ice concentration and ice thickness. We find that the spatial structure of covariances is best represented by the proportional mean-thickness analysis updates. Both physical and statistical evidence supports the experimental finding that assimilation with proportional mean-thickness updates outperforms the other two methods considered. The method described here is very simple to implement, and gives results that are sufficiently good to be used for initialising sea ice in a global climate model for seasonal to decadal predictions. |
format |
Article in Journal/Newspaper |
author |
S. Tietsche D. Notz J. H. Jungclaus J. Marotzke |
author_facet |
S. Tietsche D. Notz J. H. Jungclaus J. Marotzke |
author_sort |
S. Tietsche |
title |
Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
title_short |
Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
title_full |
Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
title_fullStr |
Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
title_full_unstemmed |
Assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
title_sort |
assimilation of sea-ice concentration in a global climate model – physical and statistical aspects |
publisher |
Copernicus Publications |
publishDate |
2013 |
url |
https://doi.org/10.5194/os-9-19-2013 https://doaj.org/article/9b71cbe2e6474e22bad77abb318987b3 |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic Sea ice |
genre_facet |
Arctic Sea ice |
op_source |
Ocean Science, Vol 9, Iss 1, Pp 19-36 (2013) |
op_relation |
http://www.ocean-sci.net/9/19/2013/os-9-19-2013.pdf https://doaj.org/toc/1812-0784 https://doaj.org/toc/1812-0792 doi:10.5194/os-9-19-2013 1812-0784 1812-0792 https://doaj.org/article/9b71cbe2e6474e22bad77abb318987b3 |
op_doi |
https://doi.org/10.5194/os-9-19-2013 |
container_title |
Ocean Science |
container_volume |
9 |
container_issue |
1 |
container_start_page |
19 |
op_container_end_page |
36 |
_version_ |
1766344138177904640 |