TY - JOUR
T1 - Extracting the buoyancy-driven atlantic meridional overturning circulation
AU - Larson, Sarah M.
AU - Buckley, Martha W.
AU - Clement, Amy C.
N1 - Funding Information:
Acknowledgments. The fully coupled CCSM4 data in this study is accessed from the NCAR Earth System Grid (ESG) online repository at https://www.earthsystemgrid.org/. SL thanks Ben Kirtman and Dan Vimont for discussions early on in this work. We also thank three anonymous reviewers for insightful comments that helped improve the manuscript. AC was supported by the NSF Climate and Large-Scale Dynamics program. MB was funded by the NOAA ESS Program (NA16OAR4310167), NASA Physical Oceanography Program (NNX17AH49G), and NSF (1558821).
Publisher Copyright:
© 2020 American Meteorological Society.
PY - 2020/6/1
Y1 - 2020/6/1
N2 - Variations in the Atlantic meridional overturning circulation (AMOC) driven by buoyancy forcing are typically characterized as having a low-frequency time scale, interhemispheric structure, cross-equatorial heat transport, and linkages to the strength of Northern Hemisphere gyre circulations and the Gulf Stream. This study first tests whether these attributes ascribed to the AMOC are reproduced in a coupled model that is mechanically decoupled and, hence, is only buoyancy coupled. Overall, the mechanically decoupled model reproduces these attributes, with the exception that in the subpolar gyre, buoyancy drives AMOC variations on interannual to multidecadal time scales, yet only the multidecadal variations penetrate into the subtropics. A stronger AMOC is associated with a strengthening of the Northern Hemisphere gyre circulations, Gulf Stream, and northward oceanic heat transport throughout the basin. We then determine whether the characteristics in the mechanically decoupled model can be recovered by low-pass filtering the AMOC in a fully coupled version of the same model, a common approach used to isolate the buoyancy-drivenAMOC.Amajor conclusion is that low-pass filtering the AMOC in the fully coupled model reproduces the buoyancy-driven AMOC pattern and most of the associated attributes, but not the statistics of the temporal variability. The strength of the AMOC-Gulf Stream connection is also not reproduced. The analyses reveal caveats that must be considered when choosing indexes and filtering techniques to estimate the buoyancy-driven AMOC. Results also provide insight on the latitudinal dependence of time scales and drivers of ocean circulation variability in coupled models, with potential implications for measurement and detection of the buoyancydriven AMOC in the real world.
AB - Variations in the Atlantic meridional overturning circulation (AMOC) driven by buoyancy forcing are typically characterized as having a low-frequency time scale, interhemispheric structure, cross-equatorial heat transport, and linkages to the strength of Northern Hemisphere gyre circulations and the Gulf Stream. This study first tests whether these attributes ascribed to the AMOC are reproduced in a coupled model that is mechanically decoupled and, hence, is only buoyancy coupled. Overall, the mechanically decoupled model reproduces these attributes, with the exception that in the subpolar gyre, buoyancy drives AMOC variations on interannual to multidecadal time scales, yet only the multidecadal variations penetrate into the subtropics. A stronger AMOC is associated with a strengthening of the Northern Hemisphere gyre circulations, Gulf Stream, and northward oceanic heat transport throughout the basin. We then determine whether the characteristics in the mechanically decoupled model can be recovered by low-pass filtering the AMOC in a fully coupled version of the same model, a common approach used to isolate the buoyancy-drivenAMOC.Amajor conclusion is that low-pass filtering the AMOC in the fully coupled model reproduces the buoyancy-driven AMOC pattern and most of the associated attributes, but not the statistics of the temporal variability. The strength of the AMOC-Gulf Stream connection is also not reproduced. The analyses reveal caveats that must be considered when choosing indexes and filtering techniques to estimate the buoyancy-driven AMOC. Results also provide insight on the latitudinal dependence of time scales and drivers of ocean circulation variability in coupled models, with potential implications for measurement and detection of the buoyancydriven AMOC in the real world.
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U2 - 10.1175/JCLI-D-19-0590.1
DO - 10.1175/JCLI-D-19-0590.1
M3 - Article
AN - SCOPUS:85085921992
VL - 33
SP - 4697
EP - 4714
JO - Journal of Climate
JF - Journal of Climate
SN - 0894-8755
IS - 11
ER -