Ocean dynamics plays a key role in driving the Atlantic Multidecadal Oscillation (AMO)

The recently proposed atmosphere-forced thermodynamics mechanism of the AMO challenged the well-known ocean dynamics mechanism, and thus it is important to identify a key feature associated with the AMO that can be used to distinguish between the two mechanisms. In this study, the spatial structure of AMO is analyzed and compared between the observations and simulations from slab ocean models and fully coupled models. The observed SST pattern of AMO is characterized by a basin-wide monopole structure, and there is a significantly high degree of spatial coherence of decadal SST variations across the entire North Atlantic basin. The observed SST anomalies over North Atlantic share a common decadal-scale signal, corresponding to the basin-wide average (i. e., the AMO). In contrast, the simulated AMO in slab ocean models exhibits a tripole-like structure, with the mid-latitude North Atlantic SST showing an inverse relationship with other parts of the basin, and the slab ocean models fail to reproduce the strong spatial coherence of decadal SST variations associated with the AMO. Further analysis using the fully coupled model simulations provides direct modeling evidence that the observed spatial coherence of decadal SST variations across North Atlantic basin can be reproduced only by including the AMOC-related ocean dynamics and the AMOC acts as a common forcing signal that results in a spatially coherent variation of North Atlantic SST.

Sun, C., Li, J., Kucharski, F. et al., 2018: Contrasting spatial structures of Atlantic Multidecadal Oscillation between observations and slab ocean model simulations, Clim. Dyn., https://doi.org/10.1007/s00382-018-4201-8

https://link.springer.com/article/10.1007%2Fs00382-018-4201-8#citeas

Image credit: Enfield, D. B., A. M. Mestas‐Nuñez, and P. J. Trimble, 2001: The Atlantic multidecadal oscillation and its relation to rainfall and river flows in the continental US. Geophys. Res. Lett.28(10), 2077-2080.

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