Balan Sarojini, B., Gregory, J. M., Tailleux, R., Bigg, G.R., Blaker, A.T., Cameron, D., Edwards, N.R., Megann, A.P., Shaffrey, L. C. and Sinha, B.
High frequency variability of the Atlantic meridional overturning circulation.
Ocean Science Discussion, 8.
To link to this item DOI: 10.5194/osd-8-219-2011
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 26N. We analyse variability on a range of timescales.
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 amplitude of the simulated annual cycle is similar to observations. 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. 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 26N. Annual volume and heat transport timeseries at the same latitude are well-correlated within 15-45N,
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 50N is not well-correlated with the AMOC at 26N.
|Date Deposited:||08 Feb 2011 11:01|
|Last Modified:||23 Apr 2017 03:05|
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