Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations
One of the most puzzling observed features of recent climate has been a multidecadal surface cooling trend over the subpolar Southern Ocean (SO). In this study we use large ensembles of simulations with multiple climate models to study the role of the SO meridional overturning circulation (MOC) in t...
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ftncar:oai:drupal-site.org:articles_25451 2024-04-28T08:39:30+00:00 Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations Zhang, Liping (author) Delworth, Thomas L. (author) Kapnick, Sarah (author) He, Jie (author) Cooke, William (author) Wittenberg, Andrew T. (author) Johnson, Nathaniel C. (author) Rosati, Anthony (author) Yang, Xiaosong (author) Lu, Feiyu (author) Bushuk, Mitchell (author) McHugh, Colleen (author) Murakami, Hiroyuki (author) Zeng, Fanrong (author) Jia, Liwei (author) Tseng, Kai-Chih (author) Morioka, Yushi (author) 2022-03-01 https://doi.org/10.1175/JCLI-D-21-0466.1 en eng Journal of Climate--0894-8755--1520-0442 articles:25451 doi:10.1175/JCLI-D-21-0466.1 ark:/85065/d7cc14dr Copyright 2022 American Meteorological Society article Text 2022 ftncar https://doi.org/10.1175/JCLI-D-21-0466.1 2024-04-04T17:34:52Z One of the most puzzling observed features of recent climate has been a multidecadal surface cooling trend over the subpolar Southern Ocean (SO). In this study we use large ensembles of simulations with multiple climate models to study the role of the SO meridional overturning circulation (MOC) in these sea surface temperature (SST) trends. We find that multiple competing processes play prominent roles, consistent with multiple mechanisms proposed in the literature for the observed cooling. Early in the simulations (twentieth century and early twenty-first century) internal variability of the MOC can have a large impact, in part due to substantial simulated multidecadal variability of the MOC. Ensemble members with initially strong convection (and related surface warming due to convective mixing of subsurface warmth to the surface) tend to subsequently cool at the surface as convection associated with internal variability weakens. A second process occurs in the late-twentieth and twenty-first centuries, as weakening of oceanic convection associated with global warming and high-latitude freshening can contribute to the surface cooling trend by suppressing convection and associated vertical mixing of subsurface heat. As the simulations progress, the multidecadal SO variability is suppressed due to forced changes in the mean state and increased oceanic stratification. As a third process, the shallower mixed layers can then rapidly warm due to increasing forcing from greenhouse gas warming. Also, during this period the ensemble spread of SO SST trend partly arises from the spread of the wind-driven Deacon cell strength. Thus, different processes could conceivably have led to the observed cooling trend, consistent with the range of possibilities presented in the literature. To better understand the causes of the observed trend, it is important to better understand the characteristics of internal low-frequency variability in the SO and the response of that variability to global warming. Article in Journal/Newspaper Southern Ocean OpenSky (NCAR/UCAR - National Center for Atmospheric Research/University Corporation for Atmospheric Research) Journal of Climate 35 5 1577 1596 |
institution |
Open Polar |
collection |
OpenSky (NCAR/UCAR - National Center for Atmospheric Research/University Corporation for Atmospheric Research) |
op_collection_id |
ftncar |
language |
English |
description |
One of the most puzzling observed features of recent climate has been a multidecadal surface cooling trend over the subpolar Southern Ocean (SO). In this study we use large ensembles of simulations with multiple climate models to study the role of the SO meridional overturning circulation (MOC) in these sea surface temperature (SST) trends. We find that multiple competing processes play prominent roles, consistent with multiple mechanisms proposed in the literature for the observed cooling. Early in the simulations (twentieth century and early twenty-first century) internal variability of the MOC can have a large impact, in part due to substantial simulated multidecadal variability of the MOC. Ensemble members with initially strong convection (and related surface warming due to convective mixing of subsurface warmth to the surface) tend to subsequently cool at the surface as convection associated with internal variability weakens. A second process occurs in the late-twentieth and twenty-first centuries, as weakening of oceanic convection associated with global warming and high-latitude freshening can contribute to the surface cooling trend by suppressing convection and associated vertical mixing of subsurface heat. As the simulations progress, the multidecadal SO variability is suppressed due to forced changes in the mean state and increased oceanic stratification. As a third process, the shallower mixed layers can then rapidly warm due to increasing forcing from greenhouse gas warming. Also, during this period the ensemble spread of SO SST trend partly arises from the spread of the wind-driven Deacon cell strength. Thus, different processes could conceivably have led to the observed cooling trend, consistent with the range of possibilities presented in the literature. To better understand the causes of the observed trend, it is important to better understand the characteristics of internal low-frequency variability in the SO and the response of that variability to global warming. |
author2 |
Zhang, Liping (author) Delworth, Thomas L. (author) Kapnick, Sarah (author) He, Jie (author) Cooke, William (author) Wittenberg, Andrew T. (author) Johnson, Nathaniel C. (author) Rosati, Anthony (author) Yang, Xiaosong (author) Lu, Feiyu (author) Bushuk, Mitchell (author) McHugh, Colleen (author) Murakami, Hiroyuki (author) Zeng, Fanrong (author) Jia, Liwei (author) Tseng, Kai-Chih (author) Morioka, Yushi (author) |
format |
Article in Journal/Newspaper |
title |
Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations |
spellingShingle |
Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations |
title_short |
Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations |
title_full |
Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations |
title_fullStr |
Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations |
title_full_unstemmed |
Roles of meridional overturning in subpolar Southern Ocean SST trends: Insights from ensemble simulations |
title_sort |
roles of meridional overturning in subpolar southern ocean sst trends: insights from ensemble simulations |
publishDate |
2022 |
url |
https://doi.org/10.1175/JCLI-D-21-0466.1 |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
Journal of Climate--0894-8755--1520-0442 articles:25451 doi:10.1175/JCLI-D-21-0466.1 ark:/85065/d7cc14dr |
op_rights |
Copyright 2022 American Meteorological Society |
op_doi |
https://doi.org/10.1175/JCLI-D-21-0466.1 |
container_title |
Journal of Climate |
container_volume |
35 |
container_issue |
5 |
container_start_page |
1577 |
op_container_end_page |
1596 |
_version_ |
1797570500838293504 |