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Geofysisk institutt

GFI/BCCR Seminar | Mads Bruun Poulsen: Mesoscale eddies in the Southern Ocean and their representation in coarse resolution ocean models

Mads Bruun Poulsen (Niels Bohr Institute, University of Copenhagen)

Mesoscale eddies in the Southern Ocean and their representation in coarse resolution ocean models

The Southern Ocean plays a central role in the modern view of the ocean general circulation where strong atmospheric westerlies allow water to upwell to the ocean surface and hence provide closure to the meridional overturning circulation. Observations have shown that the westerlies have intensified throughout the last six decades as part of contemporary climate change, with possible implications for the overturning strength and atmospheric carbon dioxide concentration. Recent idealized modelling studies have however reported that mesoscale eddies render the Southern Ocean insensitive to such wind stress change by compensating the overturning response, and that this effect is not well represented by the current generation of eddy parameterisations implemented in coarse resolution ocean general circulation models.

This statement is here assessed with a suite of Southern Ocean wind stress experiments conducted with both an eddy-resolving and a coarse resolution ocean general circulation model. The simulations show that the parameterised sensitivity to wind stress change matches the sensitivity found in a model with explicit eddies if the parameterisation is formulated correctly. However, the experiments also reveal that the parameterisation is less skillful in reproducing the mean-state of the high resolution model with respect to the meridional heat transport and vertical structure in the overturning circulation.