Séminaire
Today we are receiving the visit of Kate Snow and Alice Barthel, who will give us two half-length seminar on deep overflows and jet-topography interactions.
Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) control the abyssal limb of the global overturning circulation and play a major role in oceanic heat uptake and carbon storage. However, current general circulation models are unable to resolve the observed AABW and NADW formation and transport processes. One key process, that of overflows, motivates the need for overflow parameterizations. Most existing parameterizations have been designed with NADW overflows in mind, which differ significantly from the source regions and overflows in the Antarctic region. Given that testing of overflow schemes in the Antarctic region is ad hoc, a sensitivity study of both AABW and NADW properties to three current parameterizations is presented using a coarse resolution ocean-sea ice model within a realistic-topography sector of the Atlantic Ocean.
Overflow parameterizations that affect only tracer equations are compared to a fully dynamical Lagrangian point particle method. Despite the improved dynamics within the Lagrangian method, steep Antarctic continental slopes spanning only 2-3 grid cells at 1 degree resolutions restricts the influence of the parameterization on AABW. Overall, no current overflow parameterization is able to significantly impact AABW circulation and properties compared to the effects provided for NADW. An overflow parameterization involving partial convective mixing of tracers is most efficient at transporting dense NADW water downslope. Such a parameterization leads to a maximum mean increase in density in the north of 0.027 kg/m^3 and a decrease in age of 525 years (53%).