Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states
This study examines criteria for the existence of two stable states of the Atlantic Meridional Overturning Circulation (AMOC) using a combination of theory and simulations from a numerical coupled atmosphere–ocean climate model. By formulating a simple collection of state parameters and their relati...
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ftunswworks:oai:unsworks.library.unsw.edu.au:1959.4/unsworks_41954 2024-05-12T07:54:23+00:00 Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states Sijp, WP England, MH Gregory, JM 2012 http://hdl.handle.net/1959.4/unsworks_41954 https://doi.org/10.1175/2011JCLI4245.1 unknown American Meteorological Soc http://purl.org/au-research/grants/arc/FL100100214 http://hdl.handle.net/1959.4/unsworks_41954 https://doi.org/10.1175/2011JCLI4245.1 metadata only access http://purl.org/coar/access_right/c_14cb CC-BY-NC-ND https://creativecommons.org/licenses/by-nc-nd/4.0/ urn:ISSN:0894-8755 urn:ISSN:1520-0442 Journal of Climate, 25, 1, 282-298 13 Climate Action anzsrc-for: 040503 Physical Oceanography anzsrc-for: 0401 Atmospheric Sciences anzsrc-for: 0405 Oceanography anzsrc-for: 0909 Geomatic Engineering journal article http://purl.org/coar/resource_type/c_6501 2012 ftunswworks https://doi.org/10.1175/2011JCLI4245.1 2024-04-17T15:45:34Z This study examines criteria for the existence of two stable states of the Atlantic Meridional Overturning Circulation (AMOC) using a combination of theory and simulations from a numerical coupled atmosphere–ocean climate model. By formulating a simple collection of state parameters and their relationships, the authors reconstruct the North Atlantic Deep Water (NADW) OFF state behavior under a varying external salt-flux forcing. This part (Part I) of the paper examines the steady-state solution, which gives insight into the mechanisms that sustain the NADW OFF state in this coupled model; Part II deals with the transient behavior predicted by the evolution equation. The nonlinear behavior of the Antarctic Intermediate Water (AAIW) reverse cell is critical to the OFF state. Higher Atlantic salinity leads both to a reduced AAIW reverse cell and to a greater vertical salinity gradient in the South Atlantic. The former tends to reduce Atlantic salt export to the Southern Ocean, while the latter tends to increases it. These competing effects produce a nonlinear response of Atlantic salinity and salt export to salt forcing, and the existence of maxima in these quantities. Thus the authors obtain a natural and accurate analytical saddle-node condition for the maximal surface salt flux for which a NADW OFF state exists. By contrast, the bistability indicator proposed by De Vries and Weber does not generally work in this model. It is applicable only when the effect of the AAIW reverse cell on the Atlantic salt budget is weak. Article in Journal/Newspaper Antarc* Antarctic NADW North Atlantic Deep Water North Atlantic Southern Ocean UNSW Sydney (The University of New South Wales): UNSWorks Antarctic Southern Ocean The Antarctic Journal of Climate 25 1 282 298 |
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UNSW Sydney (The University of New South Wales): UNSWorks |
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ftunswworks |
language |
unknown |
topic |
13 Climate Action anzsrc-for: 040503 Physical Oceanography anzsrc-for: 0401 Atmospheric Sciences anzsrc-for: 0405 Oceanography anzsrc-for: 0909 Geomatic Engineering |
spellingShingle |
13 Climate Action anzsrc-for: 040503 Physical Oceanography anzsrc-for: 0401 Atmospheric Sciences anzsrc-for: 0405 Oceanography anzsrc-for: 0909 Geomatic Engineering Sijp, WP England, MH Gregory, JM Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states |
topic_facet |
13 Climate Action anzsrc-for: 040503 Physical Oceanography anzsrc-for: 0401 Atmospheric Sciences anzsrc-for: 0405 Oceanography anzsrc-for: 0909 Geomatic Engineering |
description |
This study examines criteria for the existence of two stable states of the Atlantic Meridional Overturning Circulation (AMOC) using a combination of theory and simulations from a numerical coupled atmosphere–ocean climate model. By formulating a simple collection of state parameters and their relationships, the authors reconstruct the North Atlantic Deep Water (NADW) OFF state behavior under a varying external salt-flux forcing. This part (Part I) of the paper examines the steady-state solution, which gives insight into the mechanisms that sustain the NADW OFF state in this coupled model; Part II deals with the transient behavior predicted by the evolution equation. The nonlinear behavior of the Antarctic Intermediate Water (AAIW) reverse cell is critical to the OFF state. Higher Atlantic salinity leads both to a reduced AAIW reverse cell and to a greater vertical salinity gradient in the South Atlantic. The former tends to reduce Atlantic salt export to the Southern Ocean, while the latter tends to increases it. These competing effects produce a nonlinear response of Atlantic salinity and salt export to salt forcing, and the existence of maxima in these quantities. Thus the authors obtain a natural and accurate analytical saddle-node condition for the maximal surface salt flux for which a NADW OFF state exists. By contrast, the bistability indicator proposed by De Vries and Weber does not generally work in this model. It is applicable only when the effect of the AAIW reverse cell on the Atlantic salt budget is weak. |
format |
Article in Journal/Newspaper |
author |
Sijp, WP England, MH Gregory, JM |
author_facet |
Sijp, WP England, MH Gregory, JM |
author_sort |
Sijp, WP |
title |
Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states |
title_short |
Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states |
title_full |
Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states |
title_fullStr |
Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states |
title_full_unstemmed |
Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states |
title_sort |
precise calculations of the existence of multiple amoc equilibria in coupled climate models. part i: equilibrium states |
publisher |
American Meteorological Soc |
publishDate |
2012 |
url |
http://hdl.handle.net/1959.4/unsworks_41954 https://doi.org/10.1175/2011JCLI4245.1 |
geographic |
Antarctic Southern Ocean The Antarctic |
geographic_facet |
Antarctic Southern Ocean The Antarctic |
genre |
Antarc* Antarctic NADW North Atlantic Deep Water North Atlantic Southern Ocean |
genre_facet |
Antarc* Antarctic NADW North Atlantic Deep Water North Atlantic Southern Ocean |
op_source |
urn:ISSN:0894-8755 urn:ISSN:1520-0442 Journal of Climate, 25, 1, 282-298 |
op_relation |
http://purl.org/au-research/grants/arc/FL100100214 http://hdl.handle.net/1959.4/unsworks_41954 https://doi.org/10.1175/2011JCLI4245.1 |
op_rights |
metadata only access http://purl.org/coar/access_right/c_14cb CC-BY-NC-ND https://creativecommons.org/licenses/by-nc-nd/4.0/ |
op_doi |
https://doi.org/10.1175/2011JCLI4245.1 |
container_title |
Journal of Climate |
container_volume |
25 |
container_issue |
1 |
container_start_page |
282 |
op_container_end_page |
298 |
_version_ |
1798848911101657088 |