Previous Abstract | Back to Abstracts Page | Next Abstract
Modelling Agulhas Current System dynamics: the butterfly effect of changing the vertical stratification.
Bjoern Backeberg, Julie Deshayes, Marion Bezaud, Johnny Johannessen and Chris Reason
Nansen-Tutu Centre, Department of Oceanography, University of Cape Town
(Abstract received 01/20/2015 for session X)
ABSTRACT
Most state-of-the-art ocean models at a variety of spatial resolutions and with different numerical frameworks are unable to accurately simulate the position and variability Agulhas retroflection. This highly non-linear region of the ocean plays a crucial role in global climate, by affecting the Atlantic Meridional Overturning Circulation, through the advection of warm, salty waters from the Indian to the Atlantic Ocean. In this study two free-running simulation experiments using a regional implementation of the Hybrid Coordinate Ocean Model are analysed. Only the reference densities to which the hybrid layers revert to were changed in the two experiments, which altered the vertical stratification of the simulation experiments. Compared to satellite altimetry observations, changing the vertical stratification had a positive effect (20% improvement) on the mean position of the retroflection. By diagnosing the contributing terms of the vorticity balance, it is shown that improving the stratification, facilitates a shallower (more realistic) Agulhas Undercurrent, which in turn enables enhanced interaction with the Agulhas Current through horizontal viscosity dissipation at depth and improves the representation of the southern Agulhas Current dynamics, in particular the Agulhas retroflection. From this analysis, it is evident that changing the vertical stratification has a butterfly effect on the vorticity balance, illustrating the sensitive dependence of initial conditions, through which a small change in a nonlinear system can result in large difference at a later stage.
Previous Abstract | Back to Abstracts Page | Next Abstract
2015 LOM Workshop, Copenhagen, Denmark June 2nd - 4th, 2015