Speaker
Description
The Atlantic Ocean is crucial for many regional climate phenomena through its linkage with the AMOC. For example, modeling studies suggest that the AMOC and associated Atlantic heat transport can affect multidecadal Arctic sea ice variability. Coherent multidecadal changes among the AMOC fingerprint and inverted vertical wind shear over the main development region of Atlantic hurricanes have been found in both observations and a coupled model control simulation, supporting an important role of the AMOC in multidecadal changes of Atlantic major hurricane frequency. The decadal AMOC decline directly observed from the RAPID program is consistent with that inferred from the observed AMOC fingerprint. Multidecadal AMOC variability is underestimated in many climate models. Understanding the mechanism of multidecadal AMOC variability and the causes of its underestimation in climate models are crucial for improving simulated AMOC-related climate impacts. Recent reconstructions of the long-term mean AMOC structure reveal that the Arctic Ocean is the northern terminus of the AMOC and the density-space AMOC across the OSNAP section is linked to the section’s west-east density contrast through both thermal wind and horizontal gyre contributions across sloping isopycnals. Across the OSNAP section, the directly observed mean AMOC strength over the recent period is similar to the reconstructed long-term mean AMOC strength over the past several decades. A simple conceptual model, which is calibrated by the OSNAP observations and includes two-way Atlantic-Arctic interactions through the oceanic advection and the AMOC-induced atmosphere-ocean (or ice-ocean) coupled freshwater feedback, illustrates the multidecadal AMOC delayed oscillator mechanism. It suggests an important role of the Arctic salinity anomaly and associated delayed negative feedback in multidecadal AMOC variability. The underestimation of multidecadal AMOC variability and associated impacts in climate models is likely related to their underestimation of multidecadal Arctic salinity changes. Monitoring the potential propagations of Arctic salinity anomalies along the boundary outflow would be valuable for predicting the timing and amplitude of future AMOC changes.
| Topic | Value of AMOC observing – what have we learned? |
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