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| Titel |
High frequency variability of the Atlantic meridional overturning circulation |
| VerfasserIn |
B. Balan Sarojini, J. M. Gregory, R. Tailleux, G. R. Bigg, A. T. Blaker, D. R. Cameron, N. R. Edwards, A. P. Megann, L. C. Shaffrey, B. Sinha |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 7, no. 4 ; Nr. 7, no. 4 (2011-07-18), S.471-486 |
| Datensatznummer |
250004719
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| Publikation (Nr.) |
 copernicus.org/os-7-471-2011.pdf |
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| Zusammenfassung |
| We compare the variability of the Atlantic meridional overturning circulation
(AMOC) as simulated by the coupled climate models of the RAPID project, which
cover a wide range of resolution and complexity, and observed by the
RAPID/MOCHA array at about 26° N. We analyse variability on a range
of timescales, from five-daily to interannual. In models of all resolutions
there is substantial variability on timescales of a few days; in most AOGCMs
the amplitude of the variability is of somewhat larger magnitude than that
observed by the RAPID array, while the time-mean is within about 10 % of
the observational estimate. The amplitude of the simulated annual cycle is
similar to observations, but the shape of the annual cycle shows a spread
among the models. A dynamical decomposition shows that in the models, as in
observations, the AMOC is predominantly geostrophic (driven by pressure and
sea-level gradients), with both geostrophic and Ekman contributions to
variability, the latter being exaggerated and the former underrepresented in
models. Other ageostrophic terms, neglected in the observational estimate,
are small but not negligible. The time-mean of the western boundary current
near the latitude of the RAPID/MOCHA array has a much wider model spread than
the AMOC does, indicating large differences among models in the simulation of
the wind-driven gyre circulation, and its variability is unrealistically
small in the models. In many RAPID models and in models of the Coupled Model
Intercomparison Project Phase 3 (CMIP3), interannual variability of the
maximum of the AMOC wherever it lies, which is a commonly used model index,
is similar to interannual variability in the AMOC at 26° N. Annual
volume and heat transport timeseries at the same latitude are well-correlated
within 15–45° N, indicating the climatic importance of the AMOC. In
the RAPID and CMIP3 models, we show that the AMOC is correlated over
considerable distances in latitude, but not the whole extent of the North
Atlantic; consequently interannual variability of the AMOC at 50° N,
where it is particularly relevant to European climate, is not well-correlated
with that of the AMOC at 26° N, where it is monitored by the
RAPID/MOCHA array. |
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