Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation
A realistic circulation model of the North Atlantic ocean at 0.25° resolution (NATL025 NEMO configuration) has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on th...
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fttriple:oai:gotriple.eu:oai:doaj.org/article:9150c1eef8934896863c854f010bb398 2023-05-15T17:32:03+02:00 Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation G. Candille J.-M. Brankart P. Brasseur 2015-06-01 https://doi.org/10.5194/os-11-425-2015 http://www.ocean-sci.net/11/425/2015/os-11-425-2015.pdf https://doaj.org/article/9150c1eef8934896863c854f010bb398 en eng Copernicus Publications 1812-0784 1812-0792 doi:10.5194/os-11-425-2015 http://www.ocean-sci.net/11/425/2015/os-11-425-2015.pdf https://doaj.org/article/9150c1eef8934896863c854f010bb398 undefined Ocean Science, Vol 11, Iss 3, Pp 425-438 (2015) envir geo Journal Article https://vocabularies.coar-repositories.org/resource_types/c_6501/ 2015 fttriple https://doi.org/10.5194/os-11-425-2015 2023-01-22T17:51:29Z A realistic circulation model of the North Atlantic ocean at 0.25° resolution (NATL025 NEMO configuration) has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on the model dynamics. The main motivation for this work is to develop ensemble data assimilation methods, assimilating altimetric data from past missions Jason-1 and Envisat. The assimilation experiment is designed to provide a description of the uncertainty associated with the Gulf Stream circulation for years 2005/2006, focusing on frontal regions which are predominantly affected by unresolved dynamical scales. An ensemble based on such stochastic perturbations is first produced and evaluated using along-track altimetry observations. Then each ensemble member is updated by a square root algorithm based on the SEEK (singular evolutive extended Kalman) filter (Brasseur and Verron, 2006). These three elements – stochastic parameterization, ensemble simulation and 4-D observation operator – are then used together to perform a 4-D analysis of along-track altimetry over 10-day windows. Finally, the results of this experiment are objectively evaluated using the standard probabilistic approach developed for meteorological applications (Toth et al., 2003; Candille et al., 2007). The results show that the free ensemble – before starting the assimilation process – correctly reproduces the statistical variability over the Gulf Stream area: the system is then pretty reliable but not informative (null probabilistic resolution). Updating the free ensemble with altimetric data leads to a better reliability with an information gain of around 30% (for 10-day forecasts of the SSH variable). Diagnoses on fully independent data (i.e. data that are not assimilated, like temperature and salinity profiles) provide more contrasted results when the free and updated ensembles are compared. Article in Journal/Newspaper North Atlantic Unknown Toth ENVELOPE(-155.250,-155.250,-86.367,-86.367) Ocean Science 11 3 425 438 |
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English |
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envir geo |
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envir geo G. Candille J.-M. Brankart P. Brasseur Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation |
topic_facet |
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description |
A realistic circulation model of the North Atlantic ocean at 0.25° resolution (NATL025 NEMO configuration) has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on the model dynamics. The main motivation for this work is to develop ensemble data assimilation methods, assimilating altimetric data from past missions Jason-1 and Envisat. The assimilation experiment is designed to provide a description of the uncertainty associated with the Gulf Stream circulation for years 2005/2006, focusing on frontal regions which are predominantly affected by unresolved dynamical scales. An ensemble based on such stochastic perturbations is first produced and evaluated using along-track altimetry observations. Then each ensemble member is updated by a square root algorithm based on the SEEK (singular evolutive extended Kalman) filter (Brasseur and Verron, 2006). These three elements – stochastic parameterization, ensemble simulation and 4-D observation operator – are then used together to perform a 4-D analysis of along-track altimetry over 10-day windows. Finally, the results of this experiment are objectively evaluated using the standard probabilistic approach developed for meteorological applications (Toth et al., 2003; Candille et al., 2007). The results show that the free ensemble – before starting the assimilation process – correctly reproduces the statistical variability over the Gulf Stream area: the system is then pretty reliable but not informative (null probabilistic resolution). Updating the free ensemble with altimetric data leads to a better reliability with an information gain of around 30% (for 10-day forecasts of the SSH variable). Diagnoses on fully independent data (i.e. data that are not assimilated, like temperature and salinity profiles) provide more contrasted results when the free and updated ensembles are compared. |
format |
Article in Journal/Newspaper |
author |
G. Candille J.-M. Brankart P. Brasseur |
author_facet |
G. Candille J.-M. Brankart P. Brasseur |
author_sort |
G. Candille |
title |
Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation |
title_short |
Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation |
title_full |
Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation |
title_fullStr |
Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation |
title_full_unstemmed |
Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation |
title_sort |
assessment of an ensemble system that assimilates jason-1/envisat altimeter data in a probabilistic model of the north atlantic ocean circulation |
publisher |
Copernicus Publications |
publishDate |
2015 |
url |
https://doi.org/10.5194/os-11-425-2015 http://www.ocean-sci.net/11/425/2015/os-11-425-2015.pdf https://doaj.org/article/9150c1eef8934896863c854f010bb398 |
long_lat |
ENVELOPE(-155.250,-155.250,-86.367,-86.367) |
geographic |
Toth |
geographic_facet |
Toth |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Ocean Science, Vol 11, Iss 3, Pp 425-438 (2015) |
op_relation |
1812-0784 1812-0792 doi:10.5194/os-11-425-2015 http://www.ocean-sci.net/11/425/2015/os-11-425-2015.pdf https://doaj.org/article/9150c1eef8934896863c854f010bb398 |
op_rights |
undefined |
op_doi |
https://doi.org/10.5194/os-11-425-2015 |
container_title |
Ocean Science |
container_volume |
11 |
container_issue |
3 |
container_start_page |
425 |
op_container_end_page |
438 |
_version_ |
1766129988319313920 |