Interdisciplinary seminar by Théophile Dewulf

Speaker: Théophile Dewulf, ENS Lyon

Title: Dynamics of the Southern Ocean in a model of the rotating annulus experiment: Meridional Heat transport in the presence of a meridional barrier

Abstract: In this three months summer project, we got acquainted with and tried to modify the Met Office/Oxford Rotating Annulus Laboratory Simulation (MORALS) code. This suite of program is used to simulate the flow inside the differentially heated rotating annulus experiment. This experiment consists of a fluid encapsulated between two concentric cylinders. The ensemble is rotating as a solid body, while the inner cylinder is maintained at a lower temperature than the outer one. Imposing this temperature gradient then classically leads to the development of a meridional overturning circulation, which is balanced by Coriolis forces thus creating a zonal flow. Our project meant to add a radial barrier connecting the inner and outer cylinders, completely between blocking the zonal flow. This fundamentally changes the topology of the domain, and thus has profound links to the theoretical understanding we have of the experiment. Furthermore, we use it as an analogy of the Antarctic Circumpolar Current and its response to the Drake Passage constriction in a geologically changing context. Indeed, the opening of multiple passways between continental mass around ~34 million years ago is suspected to have isolated the Antarctic from the warmth of the Equator, through the means of a strong zonal current circumnavigating the former. The added meridional wall in the simulated experiment is used to observe the difference between experiments with an open annulus and those with a closed one. The modification proved challenging, as the method of integration of MORALS is ill-adapted to the complex geometry of the tank, at least according to our findings. Preliminary simulations were performed nevertheless, and showed promising results. The effect of the meridional barrier on heat flow showed credibility in the idea the Drake Passage opening helped Antarctic glaciation. Additionally, performing this experiment numerically offered closer insight into the structure of the flow, thus helping understand previous experiments.