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A multi-model comparison of Atlantic multidecadal variability |
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| Authors: | Jin Ba Noel S Keenlyside Mojib Latif Wonsun Park Hui Ding Katja Lohmann Juliette Mignot Matthew Menary Odd Helge Otterå Bert Wouters David Salas y Melia Akira Oka Alessio Bellucci Evgeny Volodin |
| Institution: | 1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany 2. Geophysical Institute and Bjerknes Centre, University of Bergen, Bergen, Norway 3. Max Planck Institute for Meteorology, Hamburg, Germany 14. Climate and Environmental Physics, Institute of Physics and Oeschger Center of Climate Research, University of Bern, Bern, Switzerland 4. LOCEAN/IPSL, UPMC/CNRS/IRD/MNHN, University Pierre and Marie Curie, Paris, France 5. Met Office Hadley Center, Exeter, UK 6. Uni Research and the Bjerknes Centre, Bergen, Norway 12. School of Geographical Science, University of Bristol, Bristol, UK 13. Department of Physics, University of Colorado at Boulder, Boulder, CO, USA 7. Royal Netherlands Meteorological Institute, De Bilt, The Netherlands 8. CNRM/GAME, Météo-France/CNRS, Toulouse, France 9. Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan 10. Centro Euro-Mediterraneo per i Cambiamenti Climatici, CCMC, Bologna, Italy 11. Institute of Numerical Mathematics RAS, INMRAS, Moscow, Russia |
| Abstract: | A multi-model analysis of Atlantic multidecadal variability is performed with the following aims: to investigate the similarities to observations; to assess the strength and relative importance of the different elements of the mechanism proposed by Delworth et al. (J Clim 6:1993–2011, 1993) (hereafter D93) among coupled general circulation models (CGCMs); and to relate model differences to mean systematic error. The analysis is performed with long control simulations from ten CGCMs, with lengths ranging between 500 and 3600 years. In most models the variations of sea surface temperature (SST) averaged over North Atlantic show considerable power on multidecadal time scales, but with different periodicity. The SST variations are largest in the mid-latitude region, consistent with the short instrumental record. Despite large differences in model configurations, we find quite some consistency among the models in terms of processes. In eight of the ten models the mid-latitude SST variations are significantly correlated with fluctuations in the Atlantic meridional overturning circulation (AMOC), suggesting a link to northward heat transport changes. Consistent with this link, the three models with the weakest AMOC have the largest cold SST bias in the North Atlantic. There is no linear relationship on decadal timescales between AMOC and North Atlantic Oscillation in the models. Analysis of the key elements of the D93 mechanisms revealed the following: Most models present strong evidence that high-latitude winter mixing precede AMOC changes. However, the regions of wintertime convection differ among models. In most models salinity-induced density anomalies in the convective region tend to lead AMOC, while temperature-induced density anomalies lead AMOC only in one model. However, analysis shows that salinity may play an overly important role in most models, because of cold temperature biases in their relevant convective regions. In most models subpolar gyre variations tend to lead AMOC changes, and this relation is strong in more than half of the models. |
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