|Another reason why simple discretizations of rotated diffusion operators cause problems in ocean models: comments on "Isoneutral diffusion in a z-coordinate ocean model"|
Beckers, J.-M.; Burchard, H.; Campin, J.M.; Deleersnijder, E.; Mathieu, P.-P. (1998). Another reason why simple discretizations of rotated diffusion operators cause problems in ocean models: comments on "Isoneutral diffusion in a z-coordinate ocean model". J. Phys. Oceanogr. 28: 1552-1559
In: Journal of Physical Oceanography. American Meteorological Society: Boston, etc.,. ISSN 0022-3670, more
Coastal waters; Diffusion; Isopycnic surfaces; Isopycnics; Models; Ocean circulation; Marine
|Authors|| || Top |
- Beckers, J.-M., more
- Burchard, H.
- Campin, J.M.
- Deleersnijder, E., more
- Mathieu, P.-P.
In recent papers the problem of isopycnal diffusion and Gent-McWilliams stirring in z-coordinate models was reviewed and a new discretization proposed. It was shown that classical discretization needs rather heavy background diffusion along the grid lines in order to stabilize the scheme. Griffies et al. show the possible origin of the problem: one reason is the imperfect balancing of temperature and salinity diffusive fluxes along neutral surfaces and the other one the existence in the Cox discretization of a 2 Delta x mode invisible to the cross derivative in the isopycnal diffusion. The authors then present solutions, which they show to work properly in an experiment for long climate runs. Here, we will broaden the discussion of the problem by pinning up another basic numerical difficulty in discretizing rotated diffusion operators. We will also not limit ourselves to isopycnal diffusion in z-coordinate models, as the well-known GFDL MOM2 (Modular Ocean Model), but work in a more general context in which coastal ocean models such as SPEM (Semi-Spectral Primitive Equation Ocean Circulation Model) along terrain-following coordinates may use rotated diffusion operators to obtain isopycnal or geopotential diffusion.