Optimal excitation of interannual atlantic meridional overturning circulation variability
The optimal excitation of Atlantic meridional overturning circulation (MOC) anomalies is investigated in an ocean general circulation model with an idealized configuration. The optimal three-dimensional spatial structure of temperature and salinity perturbations, defined as the leading singular vect...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | en_US |
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American Meteorological Society
2011
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| Online Access: | http://hdl.handle.net/1721.1/65126 https://orcid.org/0000-0003-3925-6161 |
| _version_ | 1811079744997818368 |
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| author | Zanna, Laure Heimbach, Patrick Moore, Andrew M. Tziperman, Eli |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Zanna, Laure Heimbach, Patrick Moore, Andrew M. Tziperman, Eli |
| author_sort | Zanna, Laure |
| collection | MIT |
| description | The optimal excitation of Atlantic meridional overturning circulation (MOC) anomalies is investigated in an ocean general circulation model with an idealized configuration. The optimal three-dimensional spatial structure of temperature and salinity perturbations, defined as the leading singular vector and generating the maximum amplification of MOC anomalies, is evaluated by solving a generalized eigenvalue problem using tangent linear and adjoint models. Despite the stable linearized dynamics, a large amplification of MOC anomalies, mostly due to the interference of nonnormal modes, is initiated by the optimal perturbations.
The largest amplification of MOC anomalies, found to be excited by high-latitude deep density perturbations in the northern part of the basin, is achieved after about 7.5 years. The anomalies grow as a result of a conversion of mean available potential energy into potential and kinetic energy of the perturbations, reminiscent of baroclinic instability. The time scale of growth of MOC anomalies can be understood by examining the time evolution of deep zonal density gradients, which are related to the MOC via the thermal wind relation. The velocity of propagation of the density anomalies, found to depend on the horizontal component of the mean flow velocity and the mean density gradient, determines the growth time scale of the MOC anomalies and therefore provides an upper bound on the MOC predictability time.
The results suggest that the nonnormal linearized ocean dynamics can give rise to enhanced MOC variability if, for instance, overflows, eddies, and/or deep convection can excite high-latitude density anomalies in the ocean interior with a structure resembling that of the optimal perturbations found in this study. The findings also indicate that errors in ocean initial conditions or in model parameterizations or processes, particularly at depth, may significantly reduce the Atlantic MOC predictability time to less than a decade. |
| first_indexed | 2024-09-23T11:19:52Z |
| format | Article |
| id | mit-1721.1/65126 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T11:19:52Z |
| publishDate | 2011 |
| publisher | American Meteorological Society |
| record_format | dspace |
| spelling | mit-1721.1/651262022-10-01T02:52:15Z Optimal excitation of interannual atlantic meridional overturning circulation variability Zanna, Laure Heimbach, Patrick Moore, Andrew M. Tziperman, Eli Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Heimbach, Patrick Heimbach, Patrick The optimal excitation of Atlantic meridional overturning circulation (MOC) anomalies is investigated in an ocean general circulation model with an idealized configuration. The optimal three-dimensional spatial structure of temperature and salinity perturbations, defined as the leading singular vector and generating the maximum amplification of MOC anomalies, is evaluated by solving a generalized eigenvalue problem using tangent linear and adjoint models. Despite the stable linearized dynamics, a large amplification of MOC anomalies, mostly due to the interference of nonnormal modes, is initiated by the optimal perturbations. The largest amplification of MOC anomalies, found to be excited by high-latitude deep density perturbations in the northern part of the basin, is achieved after about 7.5 years. The anomalies grow as a result of a conversion of mean available potential energy into potential and kinetic energy of the perturbations, reminiscent of baroclinic instability. The time scale of growth of MOC anomalies can be understood by examining the time evolution of deep zonal density gradients, which are related to the MOC via the thermal wind relation. The velocity of propagation of the density anomalies, found to depend on the horizontal component of the mean flow velocity and the mean density gradient, determines the growth time scale of the MOC anomalies and therefore provides an upper bound on the MOC predictability time. The results suggest that the nonnormal linearized ocean dynamics can give rise to enhanced MOC variability if, for instance, overflows, eddies, and/or deep convection can excite high-latitude density anomalies in the ocean interior with a structure resembling that of the optimal perturbations found in this study. The findings also indicate that errors in ocean initial conditions or in model parameterizations or processes, particularly at depth, may significantly reduce the Atlantic MOC predictability time to less than a decade. 2011-08-12T18:14:20Z 2011-08-12T18:14:20Z 2011-01 2010-01 Article http://purl.org/eprint/type/JournalArticle 1520-0442 0894-8755 http://hdl.handle.net/1721.1/65126 Zanna, Laure et al. “Optimal Excitation of Interannual Atlantic Meridional Overturning Circulation Variability.” Journal of Climate 24.2 (2011) : 413-427. © 2011 American Meteorological Society https://orcid.org/0000-0003-3925-6161 en_US http://dx.doi.org/10.1175/2010JCLI3610.1 Journal of Climate Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Meteorological Society American Meteorological Society |
| spellingShingle | Zanna, Laure Heimbach, Patrick Moore, Andrew M. Tziperman, Eli Optimal excitation of interannual atlantic meridional overturning circulation variability |
| title | Optimal excitation of interannual atlantic meridional overturning circulation variability |
| title_full | Optimal excitation of interannual atlantic meridional overturning circulation variability |
| title_fullStr | Optimal excitation of interannual atlantic meridional overturning circulation variability |
| title_full_unstemmed | Optimal excitation of interannual atlantic meridional overturning circulation variability |
| title_short | Optimal excitation of interannual atlantic meridional overturning circulation variability |
| title_sort | optimal excitation of interannual atlantic meridional overturning circulation variability |
| url | http://hdl.handle.net/1721.1/65126 https://orcid.org/0000-0003-3925-6161 |
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