Several model physics options are available to users of MM5. They are briefly noted below. The model physics options are further discussed and compared in Dudhia et al. [1998].
There are four atmospheric radiation cooling schemes available in MM5: none, simple cooling, the Dudhia long and short wave radiation scheme, and the NCAR/CCM2 radiation scheme.
There are currently six convective parameterization schemes available in MM5: Anthes-Kuo, Fritsch-Chappel, Arakawa-Schubert, Kain-Fritsch, Betts-Miller, and Grell. These convective parameterization schemes have been designed for use at various simulation scales, and they are not interchangeable. For example, each scheme uses different assumptions for convective coverage on the sub-grid-scale and for the convective trigger function. The convective parameterization schemes also differ greatly in CPU usage and memory requirements.
The option for no convective parameterization for the domain (e.g., explicitly resolved convection on the grid scale) is available in MM5. This option is generally used for simulations on domains with horizontal grid spacing smaller than 10 km.
Six PBL parameterization schemes are available in MM5: bulk formula, Blackadar, Burk-Thompson, MRF (Hong-Pan), Eta, Gayno-Seaman and Pleim-Xiu. These parameterizations differ the most in the turbulent closure assumptions that are used. The PBL parameterization schemes also differ greatly in CPU usage and median range forecast requirements.
The surface layer processes in MM5 have been parameterized with fluxes of momentum, sensible heat, and latent heat, following Zhang and Anthes [1982]. The energy balance equation is used to predict the changes in ground temperature. The 13 land-use categories are used to seasonally define the physical properties at each grid point (e.g., albedo, available moisture, emissivity, roughness length, and thermal inertia). In addition, a five-layer soil temperature model is available but can only be used in conjunction with the Blackadar and MRF PBL schemes.
There are six resolvable-scale (explicit grid-scale) microphysics schemes available in MM5: removal of supersaturation, the Hsie warm rain scheme, the Dudhia simple ice scheme, the Reisner mixed phase scheme, the Reisner mixed phase scheme with graupel, and the NASA/Goddard microphysics with hail/graupel. These microphysics schemes have been designed with varying degrees of complexity for different applications of the model. In addition, there are new prognostic output variables that are generated by the more sophisticated schemes. These microphysics schemes also differ greatly in CPU usage and memory requirements.