Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model
A damped oscillatory mode of the thermohaline circulation (THC), which may play a role in interdecadal climate variability, is identified in a global primitive equation model. This analysis is done under mixed boundary conditions using an adjoint of the primitive equation model. The linearized versu...
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ftharvardudash:oai:dash.harvard.edu:1/3439964 2023-05-15T17:34:58+02:00 Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model Sirkes, Ziv Tziperman, Eli 2001 application/pdf http://nrs.harvard.edu/urn-3:HUL.InstRepos:3439964 https://doi.org/10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 en_US eng American Meteorological Society http://dx.doi.org/10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 http://ams.allenpress.com/perlserv/?request=get-archive&issn=1520-0485 Journal of Physical Oceanography Sirkes, Ziv and Eli Tziperman. 2001. Identifying a damped oscillatory thermohaline mode in a general circulation model using an adjoint model. Journal of Physical Oceanography 31(8): 2297-2306. 0022-3670 http://nrs.harvard.edu/urn-3:HUL.InstRepos:3439964 doi:10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 Journal Article 2001 ftharvardudash https://doi.org/10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 2022-04-04T12:36:25Z A damped oscillatory mode of the thermohaline circulation (THC), which may play a role in interdecadal climate variability, is identified in a global primitive equation model. This analysis is done under mixed boundary conditions using an adjoint of the primitive equation model. The linearized versus nonlinear stability behavior of the model is studied by comparing the adjoint analysis to runs of the fully nonlinear model. It is shown that a steady-state solution obtained under larger amplitude freshwater surface forcing (and hence with a weaker North Atlantic overturning) is unstable, while a steadystate solution with stronger THC is stable. In a certain intermediate parameter regime it is found that the full nonlinear model state may be unstable, while the linearized analysis indicates that the model state is stable. It is proposed that this may be because either the instability mechanism at this intermediate regime is nonlinear or, while the model is linearly stable at this regime, it allows for temporary growth of small perturbations due to the non-normal nature of the problem. A clear signal of variations is not found in the amplitude of the horizontal gyre circulation, possibly indicating that the gyre effect that was found in THC oscillations in some previous studies may not be essential for the existence of the THC oscillation. The long timescale of the oscillation in the present model also seems to indicate that the gyre effect may not be a main active participant in the thermohaline oscillation mechanism. Earth and Planetary Sciences Version of Record Article in Journal/Newspaper North Atlantic Harvard University: DASH - Digital Access to Scholarship at Harvard |
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Open Polar |
collection |
Harvard University: DASH - Digital Access to Scholarship at Harvard |
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ftharvardudash |
language |
English |
description |
A damped oscillatory mode of the thermohaline circulation (THC), which may play a role in interdecadal climate variability, is identified in a global primitive equation model. This analysis is done under mixed boundary conditions using an adjoint of the primitive equation model. The linearized versus nonlinear stability behavior of the model is studied by comparing the adjoint analysis to runs of the fully nonlinear model. It is shown that a steady-state solution obtained under larger amplitude freshwater surface forcing (and hence with a weaker North Atlantic overturning) is unstable, while a steadystate solution with stronger THC is stable. In a certain intermediate parameter regime it is found that the full nonlinear model state may be unstable, while the linearized analysis indicates that the model state is stable. It is proposed that this may be because either the instability mechanism at this intermediate regime is nonlinear or, while the model is linearly stable at this regime, it allows for temporary growth of small perturbations due to the non-normal nature of the problem. A clear signal of variations is not found in the amplitude of the horizontal gyre circulation, possibly indicating that the gyre effect that was found in THC oscillations in some previous studies may not be essential for the existence of the THC oscillation. The long timescale of the oscillation in the present model also seems to indicate that the gyre effect may not be a main active participant in the thermohaline oscillation mechanism. Earth and Planetary Sciences Version of Record |
format |
Article in Journal/Newspaper |
author |
Sirkes, Ziv Tziperman, Eli |
spellingShingle |
Sirkes, Ziv Tziperman, Eli Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model |
author_facet |
Sirkes, Ziv Tziperman, Eli |
author_sort |
Sirkes, Ziv |
title |
Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model |
title_short |
Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model |
title_full |
Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model |
title_fullStr |
Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model |
title_full_unstemmed |
Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model |
title_sort |
identifying a damped oscillatory thermohaline mode in a general circulation model using an adjoint model |
publisher |
American Meteorological Society |
publishDate |
2001 |
url |
http://nrs.harvard.edu/urn-3:HUL.InstRepos:3439964 https://doi.org/10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
http://dx.doi.org/10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 http://ams.allenpress.com/perlserv/?request=get-archive&issn=1520-0485 Journal of Physical Oceanography Sirkes, Ziv and Eli Tziperman. 2001. Identifying a damped oscillatory thermohaline mode in a general circulation model using an adjoint model. Journal of Physical Oceanography 31(8): 2297-2306. 0022-3670 http://nrs.harvard.edu/urn-3:HUL.InstRepos:3439964 doi:10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 |
op_doi |
https://doi.org/10.1175/1520-0485(2001)031<2297:IADOTM>2.0.CO;2 |
_version_ |
1766133966371291136 |