5.2. Horizontal diffusion

5.2.1. Lateral Momentum Mixing

Related CPP options:

UV_MIX_GEO	Activate mixing on geopotential (constant depth) surfaces
UV_MIX_S	Activate mixing on iso-sigma (constant sigma) surfaces
UV_VIS2	Activate Laplacian horizontal mixing of momentum
UV_VIS4	Activate Bilaplacian horizontal mixing of momentum
UV_VIS_SMAGO	Activate Smagorinsky parametrization of turbulent viscosity (only with UV_VIS2)
UV_VIS_SMAGO3D	Activate 3D Smagorinsky parametrization of turbulent viscosity

Preslected options:

# ifdef UV_VIS2
#  define UV_MIX_S
#  define UV_VIS_SMAGO
# endif

#ifdef UV_VIS_SMAGO
# define VIS_COEF_3D
#endif

# ifdef UV_MIX_S
# elif defined UV_MIX_GEO
# else
# define UV_MIX_S /* Default*/
# endif# undef  UV_HADV_TVD

Explicit lateral momentum mixing may be only useful when implicit dissipation in UV_HADV_UP3 is not large enough to account for subgrid-scale turbulence resulting from large shear currents (for example in the case of western boundary currents). In this case, Smagorinsky parametrization is recommended (define UV_VIS2 below).

5.2.2. Lateral Tracer Mixing

Related CPP options:

TS_MIX_ISO	Activate mixing along isopycnal (isoneutral) surfaces
TS_MIX_GEO	Activate mixing along geopotential surfaces
TS_MIX_S	Activate mixing along iso-sigma surfaces
TS_DIF2	Activate Laplacian horizontal mixing of tracer
TS_DIF4	Activate Bilaplacian horizontal mixing of tracer
TS_MIX_IMP	Activate stabilizing correction of rotated diffusion (used with TS_MIX_ISO and TS_MIX_GEO)

Preslected options:

#ifdef TS_HADV_RSUP3 /* Rotated-Split 3rd-order scheme is: */
# define TS_HADV_C4  /* 4th-order centered advection */
# define TS_DIF4 /* + Hyperdiffusion  */
# define TS_MIX_GEO /* rotated along geopotential surfaces */
# define TS_MIX_IMP /* with Semi-Implicit Time-Stepping */
# define DIF_COEF_3D
#endif

These options are preselected in set_global_definitions.h for compliance with Advection options.