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Monday Seminar June 10

Monday 10 June at 14:15, there will be a BCCR seminar by Rong Zhang “Understanding Atlantic Multidecadal Variability and Associated Overturning Circulation from Observational, Modelling, and Theoretical Perspectives”


The seminar will take place in the Bjerknes lecture room (4th floor, room 4020). For those not able to attend in person, it will be possible to join on zoom.



Atlantic Multidecadal Variability (AMV) and associated decadal predictability have a wide range of societal and economic applications. Observational and modelling 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 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 AMOC fingerprint supports a close AMOC-AMV linkage. 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 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. To understand key AMOC processes, the mean AMOC structure over the extratropical North Atlantic and the Arctic Mediterranean is reconstructed through the Robust Diagnostic Calculation (RDC) using a high-resolution GFDL coupled model in combination with the observed hydrographic climatology. In contrast to the traditional view, the RDC results suggest that the Arctic Ocean, not the Greenland Sea, is the northern terminus of the AMOC; horizontal circulation across sloping isopycnals contributes substantially to the northeastern subpolar AMOC, whereas open ocean deep convection, in either Greenland or Labrador Seas, contributes minimally to the AMOC. Following these AMOC reconstruction results, a simple conceptual model was established to illustrate the two-way Atlantic-Arctic interactions and associated AMOC delayed oscillator mechanism, suggesting an important role of Arctic salinity anomalies in multidecadal AMOC variability. The simple conceptual model provides a theoretical framework to understand multidecadal AMOC variability, the associated two-way interactions with the Arctic, and the diverse low-frequency AMOC variability periods simulated in climate models. The underestimation of multidecadal AMOC variability and associated impacts in climate models is likely related to the underestimation of multidecadal Arctic salinity variability. Monitoring the potential downstream propagations of Arctic salinity anomalies would be valuable for predicting the timing and amplitude of future AMOC changes.


About the speaker

Rong Zhang is a senior scientist and head of the Ocean and Cryosphere division at NOAA/GFDL. She is also a faculty member of the AOS program at Princeton University. Her research focuses on Atlantic multidecadal variability and associated decadal predictability, the role of Atlantic meridional overturning circulation (AMOC) in many regional phenomena (such as Gulf Stream separation, Intertropical Convergence Zone shift, Atlantic hurricane activity, and Arctic sea ice extent), and the mechanism and fingerprints of multidecadal AMOC variability. Rong Zhang is a Fellow of the American Geophysical Union (AGU) and the American Meteorological Society (AMS), and was the 2021 AMS Bernhard Haurwitz Memorial Lecturer. She has served as Editor of Journal of Climate and served in leadership roles for the U. S. AMOC Science Team.