Master Thesis Defense by Rasmus Ranum Hansen

Title: Solving the turbulence closure problem II: Determining the deep ocean stratification

Abstract: This thesis aims to formalize the stratification of the deep ocean as a function of buoyancy and wind forcing. With the use of the ocean only model VEROS the AMOC is analysed in a idealistic Atlantic ocean model. Firstly the conclusions from Greatbatch and Lu (2003) were used as a starting point, analysing the relation between the AMOC strength and the meridonal buoyancy gradient found in Bryan (1987). Contrary to their paper we do not find that the Stommel box model closure from Bryan (1987) does not hold for low horizontal friction, but instead find it to be a good fit. We also find the southern ocean wind forcing to be in a superposition with the buoyancy forcing.
We then found that the closure described in Brüggemann and Eden (2011) is a good 2.5 dimensional prognostic model for coarse resolution models, speeding up modeling time.
Finally using a new closure following closely the theory from Bryan (1987), however without the use the desperate approximation of changing the gradient in the thermal wind relation. We find this closure to be dynamically consistent with a clear theory behind all assumptions, and we find it to match the model data as well as the old closure. We therefore suggests this new closure as a better alternative.

Supervisor: Markus Jochum
Censor: Søren E. Larsen DTU