Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model
Sea surface temperature (SST) observations are a critical data set for long-term climate reconstruction. However, their assimilation with an ensemble-based data assimilation method can degrade performance in the ocean interior due to spurious covariances. Assimilation in isopycnal coordinates can de...
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Online Access: | https://doi.org/10.3389/fclim.2022.918572 https://doaj.org/article/5be3309ee0ff4e6c919afaac96a26075 |
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fttriple:oai:gotriple.eu:oai:doaj.org/article:5be3309ee0ff4e6c919afaac96a26075 2023-05-15T17:35:27+02:00 Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model Yiguo Wang François Counillon Sébastien Barthélémy Alexander Barth 2022-12-01 https://doi.org/10.3389/fclim.2022.918572 https://doaj.org/article/5be3309ee0ff4e6c919afaac96a26075 en eng Frontiers Media S.A. 2624-9553 doi:10.3389/fclim.2022.918572 https://doaj.org/article/5be3309ee0ff4e6c919afaac96a26075 undefined Frontiers in Climate, Vol 4 (2022) vertical localization SST assimilation isopycnal coordinate EnKF reanalysis geo envir Journal Article https://vocabularies.coar-repositories.org/resource_types/c_6501/ 2022 fttriple https://doi.org/10.3389/fclim.2022.918572 2023-01-22T19:11:17Z Sea surface temperature (SST) observations are a critical data set for long-term climate reconstruction. However, their assimilation with an ensemble-based data assimilation method can degrade performance in the ocean interior due to spurious covariances. Assimilation in isopycnal coordinates can delay the degradation, but it remains problematic for long reanalysis. We introduce vertical localization for SST assimilation in the isopycnal coordinate. The tapering functions are formulated empirically from a large pre-industrial ensemble. We propose three schemes: 1) a step function with a small localization radius that updates layers from the surface down to the first layer for which insignificant correlation with SST is found, 2) a step function with a large localization radius that updates layers down to the last layer for which significant correlation with SST is found, and 3) a flattop smooth tapering function. These tapering functions vary spatially and with the calendar month and are applied to isopycnal temperature and salinity. The impact of vertical localization on reanalysis performance is tested in identical twin experiments within the Norwegian Climate Prediction Model (NorCPM) with SST assimilation over the period 1980–2010. The SST assimilation without vertical localization greatly enhances performance in the whole water column but introduces a weak degradation at intermediate depths (e.g., 2,000–4,000 m). Vertical localization greatly reduces the degradation and improves the overall accuracy of the reanalysis, in particular in the North Pacific and the North Atlantic. A weak degradation remains in some regions below 2,000 m in the Southern Ocean. Among the three schemes, scheme 2) outperforms schemes 1) and 3) for temperature and salinity. Article in Journal/Newspaper North Atlantic Southern Ocean Unknown Pacific Southern Ocean Frontiers in Climate 4 |
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Open Polar |
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fttriple |
language |
English |
topic |
vertical localization SST assimilation isopycnal coordinate EnKF reanalysis geo envir |
spellingShingle |
vertical localization SST assimilation isopycnal coordinate EnKF reanalysis geo envir Yiguo Wang François Counillon Sébastien Barthélémy Alexander Barth Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
topic_facet |
vertical localization SST assimilation isopycnal coordinate EnKF reanalysis geo envir |
description |
Sea surface temperature (SST) observations are a critical data set for long-term climate reconstruction. However, their assimilation with an ensemble-based data assimilation method can degrade performance in the ocean interior due to spurious covariances. Assimilation in isopycnal coordinates can delay the degradation, but it remains problematic for long reanalysis. We introduce vertical localization for SST assimilation in the isopycnal coordinate. The tapering functions are formulated empirically from a large pre-industrial ensemble. We propose three schemes: 1) a step function with a small localization radius that updates layers from the surface down to the first layer for which insignificant correlation with SST is found, 2) a step function with a large localization radius that updates layers down to the last layer for which significant correlation with SST is found, and 3) a flattop smooth tapering function. These tapering functions vary spatially and with the calendar month and are applied to isopycnal temperature and salinity. The impact of vertical localization on reanalysis performance is tested in identical twin experiments within the Norwegian Climate Prediction Model (NorCPM) with SST assimilation over the period 1980–2010. The SST assimilation without vertical localization greatly enhances performance in the whole water column but introduces a weak degradation at intermediate depths (e.g., 2,000–4,000 m). Vertical localization greatly reduces the degradation and improves the overall accuracy of the reanalysis, in particular in the North Pacific and the North Atlantic. A weak degradation remains in some regions below 2,000 m in the Southern Ocean. Among the three schemes, scheme 2) outperforms schemes 1) and 3) for temperature and salinity. |
format |
Article in Journal/Newspaper |
author |
Yiguo Wang François Counillon Sébastien Barthélémy Alexander Barth |
author_facet |
Yiguo Wang François Counillon Sébastien Barthélémy Alexander Barth |
author_sort |
Yiguo Wang |
title |
Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
title_short |
Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
title_full |
Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
title_fullStr |
Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
title_full_unstemmed |
Benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
title_sort |
benefit of vertical localization for sea surface temperature assimilation in isopycnal coordinate model |
publisher |
Frontiers Media S.A. |
publishDate |
2022 |
url |
https://doi.org/10.3389/fclim.2022.918572 https://doaj.org/article/5be3309ee0ff4e6c919afaac96a26075 |
geographic |
Pacific Southern Ocean |
geographic_facet |
Pacific Southern Ocean |
genre |
North Atlantic Southern Ocean |
genre_facet |
North Atlantic Southern Ocean |
op_source |
Frontiers in Climate, Vol 4 (2022) |
op_relation |
2624-9553 doi:10.3389/fclim.2022.918572 https://doaj.org/article/5be3309ee0ff4e6c919afaac96a26075 |
op_rights |
undefined |
op_doi |
https://doi.org/10.3389/fclim.2022.918572 |
container_title |
Frontiers in Climate |
container_volume |
4 |
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1766134623135334400 |