15.11.2021: Ocean Circulation and Climate Dynamics Colloquium

When?     Monday, 15. November 2021 at 3 pm
Where?    ZOOM meeting room: https://geomar-de.zoom.us/j/88447977748?pwd=KytQclhpaEVYc2NJclZMamc0QVZidz09

Meeting-ID: 884 4797 7748
Kenncode: 872578

Abstract:
Atlantic Multidecadal Variability (AMV) and associated decadal predictability have a wide range of societal and economic applications. Understanding AMV is crucial for successful decadal predictions of AMV-related climate phenomena. Observational and modeling evidence suggests an essential role of the Atlantic Meridional Overturning Circulation (AMOC) in AMV and associated decadal predictability, although this view has been frequently challenged. The Atlantic decadal predictability is much higher in fully coupled models with relatively stronger multidecadal AMOC variability and almost disappears in slab ocean models without AMOC variability. The observed key elements of AMV are crucial for understanding the underlying mechanisms and it is important to use multivariate metrics to provide a holistic picture of the observed AMV. The observed coherent multivariate variability associated with AMV cannot be explained by a direct response to stochastic atmospheric forcing or aerosol forcing, but is consistent with the impacts of multidecadal AMOC variability. The observed AMOC fingerprint also supports a close AMOC-AMV linkage. Future AMOC changes could also have significant impacts on many regional climate phenomena. However, there is no established long-term mean state of directly observed AMOC to serve as a reference for future AMOC changes, and it is challenging to determine whether model simulated AMOC mean state and future changes are reliable. To address these issues, robust diagnostic calculations (RDC) are conducted using a high-resolution global fully coupled model constrained by observed hydrographic climatology to provide a holistic picture of the long-term mean AMOC structure at northern high latitudes. In contrast to the traditional view, the RDC results suggest that the Arctic Ocean, not the Greenland Sea, is the northern terminus of the mean AMOC; horizontal circulation across sloping isopycnals contributes substantially to the mean northeastern subpolar AMOC, whereas open-ocean deep convection, in either Greenland or Labrador Seas, contributes minimally to the mean AMOC. The recently observed AMOC strength over the period 2014-2018 across the entire OSNAP section is similar to the RDC-estimated long-term mean AMOC strength over the past several decades.

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