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High Frequency Variability of the Atlantic Meridional Overturning Circulation : Volume 7, Issue 4 (18/07/2011)

By Balan Sarojini, B.

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Book Id: WPLBN0004020523
Format Type: PDF Article :
File Size: Pages 16
Reproduction Date: 2015

Title: High Frequency Variability of the Atlantic Meridional Overturning Circulation : Volume 7, Issue 4 (18/07/2011)  
Author: Balan Sarojini, B.
Volume: Vol. 7, Issue 4
Language: English
Subject: Science, Ocean, Science
Collections: Periodicals: Journal and Magazine Collection (Contemporary), Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


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Cameron, D. R., Tailleux, R., Gregory, J. M., Sarojini, B. B., Sinha, B., Bigg, G. R.,...Megann, A. P. (2011). High Frequency Variability of the Atlantic Meridional Overturning Circulation : Volume 7, Issue 4 (18/07/2011). Retrieved from

Description: National Centre for Atmospheric Science – Climate Division, Reading, UK. 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.

High frequency variability of the Atlantic meridional overturning circulation

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