On anisotropy and internal pressure errors in numerical ocean models, 
and processes near the shelf edge.

Thiem, Ø.

Dr. Scient. (PhD) thesis, University of Bergen 2004.

The thesis consists of 4 manuscripts, that are submitted and some published in scientific journals.

The first part of the thesis concerns instability due to depth variations on hexagonal grids. An 
analysis of the propagation matrix for the spatially discretized system is used to explain unphysical 
growth of the numerical solutions of the linear shallow water equations when using hexagonal grids in 
domains with variabel depth. It is shown that with a suitable weighting of the Coriolis terms, energy 
conserving and stable numerical scheme may be gained.

The second part in the thesis focus on the connection between internal pressure errors and the grid 
orientation in sigma coordinate ocean models. It is shown that the currents set up around a bell shaped 
submerged mountain actually depend on the grid orientation, and computing the internal pressure gradients 
in both the original and a rotated grid can reduce the erronous velocities if a reasonable weighting is 
chosen between the two internal pressure estimates.

In the third part of the thesis development of eddies due to an along slope barotropic jet in a shelf 
slope area was investigated. The simulations showed that when stratification was presetent the jet was 
altered and the eddies generally got weaker then in the barotrop simulation. The barotrop simulation was 
compared with results from a linear stability analysis, and the two results was in agreement.

In the last part of the thesis a numerical ocean model was used to help understanding why cold water corals 
seem to prefer to form reefs along the shelf edge. The simulations showed that passive particles had a 
tendency to penetrate the layer just above the seabed.     

 
Click here to download the thesis in pdf format.