The linear theory of the wind- and thermally-driven ocean circulation simplifies considerably if the traditional Laplacian viscosity and thermal diffusivity are replaced by a linear-decay friction and heat diffusion. Solutions of the simplified equations display all the physically important features of the standard model.
Salmon, Rick. 1986. "A simplified linear ocean circulation theory." Journal of Marine Research 44, (4). https://elischolar.library.yale.edu/journal_of_marine_research/1832