This section was contributed from the NCAR documentation by William Large ( wily@ncar.ucar.edu) and transcribed to LATEX(with apologies from me to Wily). Equation numbers are retained to match the original but some option names have been changed to match those in MOM. When time permits, the names of some variables and indices will also be changed to be consistent with their use throughout the rest of this manual. Here are some considerations to keep in mind. The Richardson number is computed as described in Section 32.2.4.1. All vertical mixing schemes use this discretization for the Richardson number. If the Prandtl number is not one and more than two tracers are used (i.e. nt>2) then the vertical diffusion coefficient for salinity is used for all subsequent passive tracers. This scheme may not work well without option gent_mcwilliams due to excessive deepening of isopycnals when penetrative convection is active. This scheme may also be exercised in a 1-D framework. Refer to Section 15.1.6. What follows is the transcribed NCAR documentation.
Option kppvmix enables the KPP Boundary Layer Mixing Scheme of
Large, McWilliams, and Doney (1994) which is based on an adaptation of
the nonlocal K-profile parameterization of Troen and Mahrt (1986) for
use as an oceanic boundary layer model. Important characteristics of
both applications are that they are consistent with similarity theory
in the surface layer, the boundary layer is capable of penetrating the
interior stratification, and turbulent transport vanishes at the
surface. The OBL (ocean boundary layer) model also has additional
desirable features. For example, turbulent shear contributes to the
diagnosed boundary layer depth, so as to make the entrainment of
buoyancy at the base of the OBL independent of the interior
stratification. Interior mixing at the base of the boundary layer (d
= h) influences the turbulence throughout the boundary layer. Also, in
the convective limit the turbulent velocity scales for both momentum
and scalars become directly proportional to w*. The problem of
determining the vertical turbulent fluxes of momentum and both active
and passive scalars throughout the OBL is closed by adding a nonlocal
transport term 
:
In practice the external forcing is first prescribed, then the boundary layer depth, h, is determined, and finally profiles of the diffusivity and nonlocal transport are computed. A complete description of this model can be found in Large et al. (1994), and what follows is based on Appendix D of that paper. The KPP scheme is activated in the model by specifying the ifdef option kppvmix. The ifdef option implicitvmix must also be specified, because the vertical mixing is done implicitly. Specifying this ifdef option also eliminates the explicit convective adjustment scheme. Other vertical mixing paramaterizations such as option constvmix or ppvmix must not be specified when using kppvmix. There are an additional three sub-options that can be specified with kppvmix: option kmixcheckekmo does an additional check against the Ekman and Monin-Obukhov length scales; option kmixnori sets the vertical viscosity and diffusivity below the boundary layer to the constant background values, fkpm and fkph which are not dependent on the local Richardson number; and option kmixdd adds a double diffusion contribution is added to the vertical diffusivity, see Large et al. (1994).