Friday, September 17, 2021 at 10:30am to 11:30amVirtual Event
Peter Rhines, University of Washington: “Dynamical controls on the Atlantic Ocean Overturning Circulation: Unfinished Business”
Abstract: Great attention has focused on the variability of the AMOC circulation, including focused arrays of moorings, repeat hydrography, intense mapping of eddies, ARGO and RAFOS floats and satellite altimetry. Yet the underlying nearly-steady circulation still needs work. Active 'tracers': potential temperature θ, salinity S and potential vorticity PV tend to be neglected in the heavy-duty numerical modeling and numerical assimilation of observations. Despite the complexity of eddies and boundary currents we still have strong dynamical control by PV/θ/S, for example in the continuing value of the simple Sverdrup balance for interior vertical vorticity, and in the remarkable plateaus and fronts of PV in the global circulation (which, finally, can be seen in textbooks like Vallis's Atmospheric and Oceanic Fluid Dynamics..but only in the recent 2d Edition!). This suggests the value of expanding the working definition of AMOC to include these three 'tracers' as coordinates. Here we discuss the relationship between PV/θ/S and circulation. With western boundary currents playing an oversized role in AMOC, we review some key history and current understanding of tracer/PV images of western, eddy-rich regions like the 'Transition Zone' where the Gulf Stream splits apart near the Grand Banks of Newfoundland. Near-boundary and interior circulations, shallow and deep, are strongly modified there. Offshore diversion of boundary currents is a recurring theme which threatens otherwise powerful observations using near-boundary moorings. Vertical shallow/deep interactions like 'barotropization' of circulation occur where eddies are strong. Recent HYCOM model simulations (figure below, Xu, Rhines & Chassignet 2018) provide a (modeldependent) example of the full scope of water-mass transformation that is lost in the zonally integrated AMOC overturning circulation. Yet the unresolved downstream impact of the Transition Zone on AMOC needs work. The nearby Subtropical Mode Water and southern Gulf Stream inertial recirculation are impacted. PV fields, and their dynamical impact, readily mapped, can guide this work. Continuing value of very simple models (analytical, numerical and laboratory-) helps both intuition and constraints for the complex ocean.
Via Zoom: https://uri-edu.zoom.us/j/2192931058
Meeting ID: 219 293 1058
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