Abstract
The spectral dependence and numerically estimated values of Kraichnan's numerically determined effective eddy viscosity in a test field model of two- and three- dimensional isotropic flow are compared to those of a strain-dependent eddy viscosity formula suggested by Smagorinsky (1963) and frequently used in spatially differenced primitive equation models of the atmosphere. The effective eddy viscosities are in general agreement in the three-dimensional case.