ChangeS ACTIVITIES

ChangeS Webinar Series 2011-2012

Dec 20th , 2011 organised by CMCC, Bologna (IT)
The adiabatic polo-to-pole overturning circulation
Dr. Paola Cessi Scripps Institution of Oceanography - University of California, San Diego

ABSTRACT

The adiabatic pole-to-pole cell of the residual overturning circulation (ROC) in the Atlantic is studied in a two-hemisphere, semi-enclosed basin, with a zonally-reentrant channel occupying the southernmost eighth of the domain. Three different models of increasing complexity are used: a simple, analytically-tractable zonally-averaged model, a coarse- resolution numerical model with parameterized eddies, and an eddy-resolving general circulation model. Two elements are found to be necessary for the existence of an adiabatic pole-to-pole cell: (1) a thermally-indirect, wind-driven overturning circulation in the zonally-reentrant channel, analogous to the Deacon cell in the Antarctic circumpolar Current (ACC) region, and (2) a set of outcropping isopycnals shared between the channel and the semi-enclosed region of the Northern Hemisphere. These points are supported by several computations varying the domain geometry, the surface buoyancy distribution and the wind-forcing. All three models give results which are qualitatively very similar, indicating that the two requirements above are general and robust. All three models illustrate how the geometry of the isopycnals is shaped by the interhemispheric ROC, leading to three major thermostads, which we identify with the major water masses of the Atlantic, i.e. North Atlantic Deep Water, Antarctic Intermediate Water and Antarctic Bottom Water. The models also illustrate how changes in buoyancy fluxes in the high latitudes of both hemispheres, as well as the strength of the winds can ccelerate or decelerate the ROC, and what their time-scales are.

Speaker: Dr. Paola Cessi

Time: Dec, 20th 2011 2:30 pm (Rome CET)
Duration: 2 hours + 15 minutes Q&A

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