Understanding variability of the Southern Ocean overturning circulation in CORE-II models
The current generation of climate models exhibit a large spread in the steady-state and projected Southern Ocean upper and lower overturning circulation, with mechanisms for deep ocean variability remaining less well understood. Here, common Southern Ocean metrics in twelve models from the Coordinat...
Published in: | Ocean Modelling |
---|---|
Main Authors: | , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Elsevier
2018
|
Subjects: | |
Online Access: | https://oceanrep.geomar.de/id/eprint/47825/ https://oceanrep.geomar.de/id/eprint/47825/1/Downes.pdf https://doi.org/10.1016/j.ocemod.2018.01.005 |
id |
ftoceanrep:oai:oceanrep.geomar.de:47825 |
---|---|
record_format |
openpolar |
spelling |
ftoceanrep:oai:oceanrep.geomar.de:47825 2023-05-15T18:24:38+02:00 Understanding variability of the Southern Ocean overturning circulation in CORE-II models Downes, S.M. Spence, P. Hogg, A.M. 2018 text https://oceanrep.geomar.de/id/eprint/47825/ https://oceanrep.geomar.de/id/eprint/47825/1/Downes.pdf https://doi.org/10.1016/j.ocemod.2018.01.005 en eng Elsevier https://oceanrep.geomar.de/id/eprint/47825/1/Downes.pdf Downes, S. M. , Spence, P. and Hogg, A. M. (2018) Understanding variability of the Southern Ocean overturning circulation in CORE-II models. Ocean Modelling, 123 . pp. 98-109. DOI 10.1016/j.ocemod.2018.01.005 <https://doi.org/10.1016/j.ocemod.2018.01.005>. doi:10.1016/j.ocemod.2018.01.005 info:eu-repo/semantics/restrictedAccess Article PeerReviewed 2018 ftoceanrep https://doi.org/10.1016/j.ocemod.2018.01.005 2023-04-07T15:47:32Z The current generation of climate models exhibit a large spread in the steady-state and projected Southern Ocean upper and lower overturning circulation, with mechanisms for deep ocean variability remaining less well understood. Here, common Southern Ocean metrics in twelve models from the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) are assessed over a 60 year period. Specifically, stratification, surface buoyancy fluxes, and eddies are linked to the magnitude of the strengthening trend in the upper overturning circulation, and a decreasing trend in the lower overturning circulation across the CORE-II models. The models evolve similarly in the upper 1 km and the deep ocean, with an almost equivalent poleward intensification trend in the Southern Hemisphere westerly winds. However, the models differ substantially in their eddy parameterisation and surface buoyancy fluxes. In general, models with a larger heat-driven water mass transformation where deep waters upwell at the surface ( ∼ 55°S) transport warmer waters into intermediate depths, thus weakening the stratification in the upper 2 km. Models with a weak eddy induced overturning and a warm bias in the intermediate waters are more likely to exhibit larger increases in the upper overturning circulation, and more significant weakening of the lower overturning circulation. We find the opposite holds for a cool model bias in intermediate depths, combined with a more complex 3D eddy parameterisation that acts to reduce isopycnal slope. In summary, the Southern Ocean overturning circulation decadal trends in the coarse resolution CORE-II models are governed by biases in surface buoyancy fluxes and the ocean density field, and the configuration of the eddy parameterisation. Article in Journal/Newspaper Southern Ocean OceanRep (GEOMAR Helmholtz Centre für Ocean Research Kiel) Southern Ocean Ocean Modelling 123 98 109 |
institution |
Open Polar |
collection |
OceanRep (GEOMAR Helmholtz Centre für Ocean Research Kiel) |
op_collection_id |
ftoceanrep |
language |
English |
description |
The current generation of climate models exhibit a large spread in the steady-state and projected Southern Ocean upper and lower overturning circulation, with mechanisms for deep ocean variability remaining less well understood. Here, common Southern Ocean metrics in twelve models from the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) are assessed over a 60 year period. Specifically, stratification, surface buoyancy fluxes, and eddies are linked to the magnitude of the strengthening trend in the upper overturning circulation, and a decreasing trend in the lower overturning circulation across the CORE-II models. The models evolve similarly in the upper 1 km and the deep ocean, with an almost equivalent poleward intensification trend in the Southern Hemisphere westerly winds. However, the models differ substantially in their eddy parameterisation and surface buoyancy fluxes. In general, models with a larger heat-driven water mass transformation where deep waters upwell at the surface ( ∼ 55°S) transport warmer waters into intermediate depths, thus weakening the stratification in the upper 2 km. Models with a weak eddy induced overturning and a warm bias in the intermediate waters are more likely to exhibit larger increases in the upper overturning circulation, and more significant weakening of the lower overturning circulation. We find the opposite holds for a cool model bias in intermediate depths, combined with a more complex 3D eddy parameterisation that acts to reduce isopycnal slope. In summary, the Southern Ocean overturning circulation decadal trends in the coarse resolution CORE-II models are governed by biases in surface buoyancy fluxes and the ocean density field, and the configuration of the eddy parameterisation. |
format |
Article in Journal/Newspaper |
author |
Downes, S.M. Spence, P. Hogg, A.M. |
spellingShingle |
Downes, S.M. Spence, P. Hogg, A.M. Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
author_facet |
Downes, S.M. Spence, P. Hogg, A.M. |
author_sort |
Downes, S.M. |
title |
Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
title_short |
Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
title_full |
Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
title_fullStr |
Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
title_full_unstemmed |
Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
title_sort |
understanding variability of the southern ocean overturning circulation in core-ii models |
publisher |
Elsevier |
publishDate |
2018 |
url |
https://oceanrep.geomar.de/id/eprint/47825/ https://oceanrep.geomar.de/id/eprint/47825/1/Downes.pdf https://doi.org/10.1016/j.ocemod.2018.01.005 |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
https://oceanrep.geomar.de/id/eprint/47825/1/Downes.pdf Downes, S. M. , Spence, P. and Hogg, A. M. (2018) Understanding variability of the Southern Ocean overturning circulation in CORE-II models. Ocean Modelling, 123 . pp. 98-109. DOI 10.1016/j.ocemod.2018.01.005 <https://doi.org/10.1016/j.ocemod.2018.01.005>. doi:10.1016/j.ocemod.2018.01.005 |
op_rights |
info:eu-repo/semantics/restrictedAccess |
op_doi |
https://doi.org/10.1016/j.ocemod.2018.01.005 |
container_title |
Ocean Modelling |
container_volume |
123 |
container_start_page |
98 |
op_container_end_page |
109 |
_version_ |
1766205388616630272 |