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...
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ftanucanberra:oai:openresearch-repository.anu.edu.au:1885/258192 2024-01-14T10:00:37+01:00 Understanding variability of the Southern Ocean overturning circulation in CORE-II models Downes, Stephanie Spence, Paul Hogg, Andrew application/pdf http://hdl.handle.net/1885/258192 https://doi.org/10.1016/j.ocemod.2018.01.005 https://openresearch-repository.anu.edu.au/bitstream/1885/258192/3/01_Downes_Understanding_variability_of_2018.pdf.jpg en_AU eng Elsevier http://purl.org/au-research/grants/arc/DE150100223 1463-5003 http://hdl.handle.net/1885/258192 doi:10.1016/j.ocemod.2018.01.005 https://openresearch-repository.anu.edu.au/bitstream/1885/258192/3/01_Downes_Understanding_variability_of_2018.pdf.jpg © 2018 The Authors Ocean Modelling CORE-II models Meridional overturning circulation Southern Ocean Eddy parameterisation Ocean stratification Water mass transformation Journal article ftanucanberra https://doi.org/10.1016/j.ocemod.2018.01.005 2023-12-15T09:35:34Z 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. SMD was supported by the Australian Governments Business Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) Article in Journal/Newspaper Antarc* Antarctic Antarctic Climate and Ecosystems Cooperative Research Centre Southern Ocean Australian National University: ANU Digital Collections Antarctic Southern Ocean The Antarctic Ocean Modelling 123 98 109 |
institution |
Open Polar |
collection |
Australian National University: ANU Digital Collections |
op_collection_id |
ftanucanberra |
language |
English |
topic |
CORE-II models Meridional overturning circulation Southern Ocean Eddy parameterisation Ocean stratification Water mass transformation |
spellingShingle |
CORE-II models Meridional overturning circulation Southern Ocean Eddy parameterisation Ocean stratification Water mass transformation Downes, Stephanie Spence, Paul Hogg, Andrew Understanding variability of the Southern Ocean overturning circulation in CORE-II models |
topic_facet |
CORE-II models Meridional overturning circulation Southern Ocean Eddy parameterisation Ocean stratification Water mass transformation |
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. SMD was supported by the Australian Governments Business Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) |
format |
Article in Journal/Newspaper |
author |
Downes, Stephanie Spence, Paul Hogg, Andrew |
author_facet |
Downes, Stephanie Spence, Paul Hogg, Andrew |
author_sort |
Downes, Stephanie |
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 |
url |
http://hdl.handle.net/1885/258192 https://doi.org/10.1016/j.ocemod.2018.01.005 https://openresearch-repository.anu.edu.au/bitstream/1885/258192/3/01_Downes_Understanding_variability_of_2018.pdf.jpg |
geographic |
Antarctic Southern Ocean The Antarctic |
geographic_facet |
Antarctic Southern Ocean The Antarctic |
genre |
Antarc* Antarctic Antarctic Climate and Ecosystems Cooperative Research Centre Southern Ocean |
genre_facet |
Antarc* Antarctic Antarctic Climate and Ecosystems Cooperative Research Centre Southern Ocean |
op_source |
Ocean Modelling |
op_relation |
http://purl.org/au-research/grants/arc/DE150100223 1463-5003 http://hdl.handle.net/1885/258192 doi:10.1016/j.ocemod.2018.01.005 https://openresearch-repository.anu.edu.au/bitstream/1885/258192/3/01_Downes_Understanding_variability_of_2018.pdf.jpg |
op_rights |
© 2018 The Authors |
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 |
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1788066493467983872 |