Response of the Southern Ocean circulation to changes in global climate
The Southern Ocean circulation plays a central role in the dynamics of past and future global climate change. However, due to a scarcity of observations and the difficulty of accurately modelling the Southern Ocean, we lack a comprehensive understanding of how the circulation responds to change. The...
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2014
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ftdatacite:10.25911/5d4ffbc732e17 2023-05-15T13:49:27+02:00 Response of the Southern Ocean circulation to changes in global climate Morrison, Adele Kim 2014 https://dx.doi.org/10.25911/5d4ffbc732e17 https://openresearch-repository.anu.edu.au/handle/1885/155903 unknown The Australian National University Ocean circulation Computer simulationAntarctic Ocean Oceanography Antarctic Ocean Ocean-atmosphere interaction Antarctic Ocean Climatic changes Other CreativeWork article Thesis (PhD) 2014 ftdatacite https://doi.org/10.25911/5d4ffbc732e17 2021-11-05T12:55:41Z The Southern Ocean circulation plays a central role in the dynamics of past and future global climate change. However, due to a scarcity of observations and the difficulty of accurately modelling the Southern Ocean, we lack a comprehensive understanding of how the circulation responds to change. The energetic eddy field directly impacts the response of the circulation, but the small scale of the eddies has generally been below the resolution of numerical ocean models. This thesis makes use of two high resolution idealised ocean models to investigate the role of eddies in modifying the response of the Southern Ocean circulation to changing wind stress and surface buoyancy forcing. The simulations demonstrate that the eddy field is significant in the dynamical response, but that the impact on different aspects of the circulation is complex and subtle. The Antarctic Circumpolar Current (ACC) transport increases only weakly in response to enhanced Southern Ocean wind stress, due to the enhanced eddy field, which efficiently eliminates momentum input. In contrast, the eddy field only partially compensates wind- driven increases in the upper overturning circulation, resulting in a moderate overturning increase in response to enhanced westerly winds. Southern Ocean heat uptake is also shown to be dependent on changes in the eddy field. Mid-depth warming occurs primarily due to a decrease in the upward eddy heat flux, associated with reduced isopycnal temperature gradients in a warmer climate. However, increased wind stress may reduce the mid-depth heat uptake; a transient cooling trend arises from the wind-driven enhancement of the vertical eddy heat flux. The uncoupled idealised models also permit an in-depth analysis of the response of the Southern Ocean overturning to changes in surface buoyancy forcing. A suite of buoyancy forcing perturbations show that mid-latitude heat and freshwater fluxes may be as significant as wind stress in altering the strength of the upper overturning circulation. Analysis of the transient model response to a range of surface buoyancy forcing perturbations also indicates that recent observations are consistent with a slowdown of the lower overturning cell. In summary, this thesis has refined our understanding of how the large scale Southern Ocean circulation responds to atmospheric change and the role of the eddy field in modifying that response. This work provides a basis to interpret the more complicated response of coupled and coarse resolution models. Thesis Antarc* Antarctic Antarctic Ocean Southern Ocean DataCite Metadata Store (German National Library of Science and Technology) Antarctic Southern Ocean The Antarctic Antarctic Ocean |
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Open Polar |
collection |
DataCite Metadata Store (German National Library of Science and Technology) |
op_collection_id |
ftdatacite |
language |
unknown |
topic |
Ocean circulation Computer simulationAntarctic Ocean Oceanography Antarctic Ocean Ocean-atmosphere interaction Antarctic Ocean Climatic changes |
spellingShingle |
Ocean circulation Computer simulationAntarctic Ocean Oceanography Antarctic Ocean Ocean-atmosphere interaction Antarctic Ocean Climatic changes Morrison, Adele Kim Response of the Southern Ocean circulation to changes in global climate |
topic_facet |
Ocean circulation Computer simulationAntarctic Ocean Oceanography Antarctic Ocean Ocean-atmosphere interaction Antarctic Ocean Climatic changes |
description |
The Southern Ocean circulation plays a central role in the dynamics of past and future global climate change. However, due to a scarcity of observations and the difficulty of accurately modelling the Southern Ocean, we lack a comprehensive understanding of how the circulation responds to change. The energetic eddy field directly impacts the response of the circulation, but the small scale of the eddies has generally been below the resolution of numerical ocean models. This thesis makes use of two high resolution idealised ocean models to investigate the role of eddies in modifying the response of the Southern Ocean circulation to changing wind stress and surface buoyancy forcing. The simulations demonstrate that the eddy field is significant in the dynamical response, but that the impact on different aspects of the circulation is complex and subtle. The Antarctic Circumpolar Current (ACC) transport increases only weakly in response to enhanced Southern Ocean wind stress, due to the enhanced eddy field, which efficiently eliminates momentum input. In contrast, the eddy field only partially compensates wind- driven increases in the upper overturning circulation, resulting in a moderate overturning increase in response to enhanced westerly winds. Southern Ocean heat uptake is also shown to be dependent on changes in the eddy field. Mid-depth warming occurs primarily due to a decrease in the upward eddy heat flux, associated with reduced isopycnal temperature gradients in a warmer climate. However, increased wind stress may reduce the mid-depth heat uptake; a transient cooling trend arises from the wind-driven enhancement of the vertical eddy heat flux. The uncoupled idealised models also permit an in-depth analysis of the response of the Southern Ocean overturning to changes in surface buoyancy forcing. A suite of buoyancy forcing perturbations show that mid-latitude heat and freshwater fluxes may be as significant as wind stress in altering the strength of the upper overturning circulation. Analysis of the transient model response to a range of surface buoyancy forcing perturbations also indicates that recent observations are consistent with a slowdown of the lower overturning cell. In summary, this thesis has refined our understanding of how the large scale Southern Ocean circulation responds to atmospheric change and the role of the eddy field in modifying that response. This work provides a basis to interpret the more complicated response of coupled and coarse resolution models. |
format |
Thesis |
author |
Morrison, Adele Kim |
author_facet |
Morrison, Adele Kim |
author_sort |
Morrison, Adele Kim |
title |
Response of the Southern Ocean circulation to changes in global climate |
title_short |
Response of the Southern Ocean circulation to changes in global climate |
title_full |
Response of the Southern Ocean circulation to changes in global climate |
title_fullStr |
Response of the Southern Ocean circulation to changes in global climate |
title_full_unstemmed |
Response of the Southern Ocean circulation to changes in global climate |
title_sort |
response of the southern ocean circulation to changes in global climate |
publisher |
The Australian National University |
publishDate |
2014 |
url |
https://dx.doi.org/10.25911/5d4ffbc732e17 https://openresearch-repository.anu.edu.au/handle/1885/155903 |
geographic |
Antarctic Southern Ocean The Antarctic Antarctic Ocean |
geographic_facet |
Antarctic Southern Ocean The Antarctic Antarctic Ocean |
genre |
Antarc* Antarctic Antarctic Ocean Southern Ocean |
genre_facet |
Antarc* Antarctic Antarctic Ocean Southern Ocean |
op_doi |
https://doi.org/10.25911/5d4ffbc732e17 |
_version_ |
1766251382913892352 |