Numerical discretization of rotated diffusion operators in ocean models

A method to improve the behavior of the numerical discretization of a rotated diffusion operator such as, for example, the isopycnal diffusion parameterization used in large-scale ocean models based on the so-called z-coordinate system is presented. The authors then focus exclusively on the dynamically passive tracers and analyze some different approaches to the numerical discretization. Monotonic schemes are designed but are found to be rather complex, while simpler, linear schemes are shown to produce unphysical undershooting and overshooting. It is suggested that the choice of an appropriate discretization method depends on the importance of the rotated diffusion in a given simulation, whether the field to be diffused is dynamically active or not

Tanganyika lake, modeling the eco-hydrodynamics

peer reviewedThe model consists of a four-component ecosystem model, coupled to a hydrodynamic model. The hydrodynamic model considers the Lake as two homogeneous layers of different density lying above each other, representing the warm epilimnion (surface mixed layer) and cold dense hypolimnion (lower layer) separated by a thermocline (Naithani et al., 2002, 2003