Pitfalls with the Numerical Representation of Isopycnal Diapycnal Mixing

Abstract

Current numerical models of ocean circulation parameterize diffusion using a diagonal diffusivity tensor in a horizontal/vertical coordinate system rather than in the isopycnal/diapycnal directions. It is pointed out that this procedure introduces a fictitious flux of density in the horizontal direction. A solution to this problem is available in the work of Redi. Also we show that care must be used in simple models of the deep ocean not to confuse the diapycnal velocity with the vertical velocity which simply occurs as a component of along isopycnal motion.