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...
| Hlavní autoři: | , , , |
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| Médium: | Journal article |
| Jazyk: | English |
| Vydáno: |
2011
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| _version_ | 1826289965007372288 |
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| author | Zanna, L Heimbach, P Moore, A Tziperman, E |
| author_facet | Zanna, L Heimbach, P Moore, A Tziperman, E |
| author_sort | Zanna, L |
| collection | OXFORD |
| 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 AtlanticMOC predictability time to less than a decade. © 2011 American Meteorological Society. |
| first_indexed | 2024-03-07T02:36:56Z |
| format | Journal article |
| id | oxford-uuid:a91ad79f-1215-42fb-94c0-dbb5fe0bbb34 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T02:36:56Z |
| publishDate | 2011 |
| record_format | dspace |
| spelling | oxford-uuid:a91ad79f-1215-42fb-94c0-dbb5fe0bbb342022-03-27T03:06:09ZOptimal Excitation of Interannual Atlantic Meridional Overturning Circulation VariabilityJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:a91ad79f-1215-42fb-94c0-dbb5fe0bbb34EnglishSymplectic Elements at Oxford2011Zanna, LHeimbach, PMoore, ATziperman, EThe 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 AtlanticMOC predictability time to less than a decade. © 2011 American Meteorological Society. |
| spellingShingle | Zanna, L Heimbach, P Moore, A Tziperman, E 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 |
| work_keys_str_mv | AT zannal optimalexcitationofinterannualatlanticmeridionaloverturningcirculationvariability AT heimbachp optimalexcitationofinterannualatlanticmeridionaloverturningcirculationvariability AT moorea optimalexcitationofinterannualatlanticmeridionaloverturningcirculationvariability AT tzipermane optimalexcitationofinterannualatlanticmeridionaloverturningcirculationvariability |