Reconciling two alternative mechanisms behind bi-decadal variability in the North AtlanticReport as inadecuate




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* Corresponding author 1 LOCEAN - Laboratoire d-Océanographie et du Climat : Expérimentations et Approches Numériques 2 EPOC - Environnements et Paléoenvironnements OCéaniques 3 PARVATI - Processus de la variabilité climatique tropicale et impacts LOCEAN - Laboratoire d-Océanographie et du Climat : Expérimentations et Approches Numériques 4 Climate and environmental physics and Oeschger Centre for climate change research 5 Ocean and earth science 6 NCAS-Climate Reading Department of Meteorology Reading

Abstract : Understanding the preferential timescales of variability in the North Atlantic, usually associated with the Atlantic meridional overturning circulation AMOC, is essential for the prospects for decadal prediction. However, the wide variety of mechanisms proposed from the analysis of climate simulations, potentially dependent on the models themselves, has stimulated the debate of which processes take place in reality. One mechanism receiving increasing attention, identified both in idealized models and observations, is a westward propagation of subsurface buoyancy anomalies that impact the AMOC through a basin-scale intensification of the zonal density gradient, enhancing the northward transport via thermal wind balance. In this study, we revisit a control simulation from the Institut Pierre-Simon Laplace Coupled Model 5A IPSL-CM5A, characterized by a strong AMOC periodicity at 20 years, previously explained by an upper ocean–atmosphere–sea ice coupled mode driving convection activity south of Iceland. Our study shows that this mechanism interacts constructively with the basin-wide propagation in the subsurface. This constructive feedback may explain why bi-decadal variability is so intense in this coupled model as compared to others.





Author: Pablo Ortega - Juliette Mignot - Didier Swingedouw - Florian Sévellec - Éric Guilyardi -

Source: https://hal.archives-ouvertes.fr/



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