Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion
The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the global climate system. In this study, using a zonally averaged ocean model, we reexamine the sensitivity of this circulation, and ocean density structure in general, to several types of external forcing. The basin o...
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ftsouthampton:oai:eprints.soton.ac.uk:339742 2023-07-30T03:58:30+02:00 Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion Sévellec, Florian Fedorov, Alexey V. 2011-09 https://eprints.soton.ac.uk/339742/ unknown Sévellec, Florian and Fedorov, Alexey V. (2011) Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion. [in special issue: Climate and the Atlantic Meridional Overturning Circulation] Deep Sea Research Part II: Topical Studies in Oceanography, 58 (17-18), 1927-1943. (doi:10.1016/j.dsr2.2010.10.070 <http://dx.doi.org/10.1016/j.dsr2.2010.10.070>). Article PeerReviewed 2011 ftsouthampton https://doi.org/10.1016/j.dsr2.2010.10.070 2023-07-09T21:39:26Z The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the global climate system. In this study, using a zonally averaged ocean model, we reexamine the sensitivity of this circulation, and ocean density structure in general, to several types of external forcing. The basin of the model extends from northern high latitudes to Antarctica and includes an implicit representation of a circumpolar channel in the South, and ocean circulation is driven by surface buoyancy fluxes and wind forcing. In contrast to earlier two-dimensional studies of the AMOC, our approach involves a careful treatment of the residual mean circulation (comprising the Eulerian-mean and eddy-induced flows), which is especially important for the Southern Ocean dynamics. Using boundary conditions consistent with present-day observations the model reproduces realistic ocean stratification and meridional overturning. The structure, intensity, and stability of the overturning are then extensively studied using three control parameters: the strength of westerly wind stress over the Southern Ocean, the magnitude of freshwater fluxes imposed on the northern Atlantic, and ocean diapycnal diffusivity. In a realistic parameter range, we estimate the AMOC sensitivity to changes in the Southern Ocean winds on the order of 1 Sv per 20% increase in the wind stress. The overturning also increases with diapycnal diffusivity, but the dependence is weaker than in the absence of the winds. The model can undergo a shutdown of the overturning (subject to a hysteresis) when either the freshwater forcing gradually increases or the wind stress decreases. The hysteresis loop disappears for large values of isopycnal diffusivity. Changes in the AMOC intensity are accompanied by changes in the volume transport of the Antarctic Circumpolar Current. Specifically, the AMOC collapse leads to a strengthening of this transport. Ultimately, our calculations produce stability maps for the steady states of the meridional overturning circulation and provide ... Article in Journal/Newspaper Antarc* Antarctic Antarctica Southern Ocean University of Southampton: e-Prints Soton Antarctic Southern Ocean The Antarctic Deep Sea Research Part II: Topical Studies in Oceanography 58 17-18 1927 1943 |
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Open Polar |
collection |
University of Southampton: e-Prints Soton |
op_collection_id |
ftsouthampton |
language |
unknown |
description |
The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the global climate system. In this study, using a zonally averaged ocean model, we reexamine the sensitivity of this circulation, and ocean density structure in general, to several types of external forcing. The basin of the model extends from northern high latitudes to Antarctica and includes an implicit representation of a circumpolar channel in the South, and ocean circulation is driven by surface buoyancy fluxes and wind forcing. In contrast to earlier two-dimensional studies of the AMOC, our approach involves a careful treatment of the residual mean circulation (comprising the Eulerian-mean and eddy-induced flows), which is especially important for the Southern Ocean dynamics. Using boundary conditions consistent with present-day observations the model reproduces realistic ocean stratification and meridional overturning. The structure, intensity, and stability of the overturning are then extensively studied using three control parameters: the strength of westerly wind stress over the Southern Ocean, the magnitude of freshwater fluxes imposed on the northern Atlantic, and ocean diapycnal diffusivity. In a realistic parameter range, we estimate the AMOC sensitivity to changes in the Southern Ocean winds on the order of 1 Sv per 20% increase in the wind stress. The overturning also increases with diapycnal diffusivity, but the dependence is weaker than in the absence of the winds. The model can undergo a shutdown of the overturning (subject to a hysteresis) when either the freshwater forcing gradually increases or the wind stress decreases. The hysteresis loop disappears for large values of isopycnal diffusivity. Changes in the AMOC intensity are accompanied by changes in the volume transport of the Antarctic Circumpolar Current. Specifically, the AMOC collapse leads to a strengthening of this transport. Ultimately, our calculations produce stability maps for the steady states of the meridional overturning circulation and provide ... |
format |
Article in Journal/Newspaper |
author |
Sévellec, Florian Fedorov, Alexey V. |
spellingShingle |
Sévellec, Florian Fedorov, Alexey V. Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion |
author_facet |
Sévellec, Florian Fedorov, Alexey V. |
author_sort |
Sévellec, Florian |
title |
Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion |
title_short |
Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion |
title_full |
Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion |
title_fullStr |
Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion |
title_full_unstemmed |
Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion |
title_sort |
stability of the atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: effects of freshwater flux, southern ocean winds, and diapycnal diffusion |
publishDate |
2011 |
url |
https://eprints.soton.ac.uk/339742/ |
geographic |
Antarctic Southern Ocean The Antarctic |
geographic_facet |
Antarctic Southern Ocean The Antarctic |
genre |
Antarc* Antarctic Antarctica Southern Ocean |
genre_facet |
Antarc* Antarctic Antarctica Southern Ocean |
op_relation |
Sévellec, Florian and Fedorov, Alexey V. (2011) Stability of the Atlantic meridional overturning circulation and stratification in a zonally averaged ocean model: Effects of freshwater flux, Southern Ocean winds, and diapycnal diffusion. [in special issue: Climate and the Atlantic Meridional Overturning Circulation] Deep Sea Research Part II: Topical Studies in Oceanography, 58 (17-18), 1927-1943. (doi:10.1016/j.dsr2.2010.10.070 <http://dx.doi.org/10.1016/j.dsr2.2010.10.070>). |
op_doi |
https://doi.org/10.1016/j.dsr2.2010.10.070 |
container_title |
Deep Sea Research Part II: Topical Studies in Oceanography |
container_volume |
58 |
container_issue |
17-18 |
container_start_page |
1927 |
op_container_end_page |
1943 |
_version_ |
1772821285068341248 |