Quoted from: http://www.atmet.com/html/docs/documentation.shtml 

      RAMS, the Regional Atmospheric Modeling System, is a highly versatile numerical code developed by several groups over the years, including the scientists at Colorado State University, the *ASTER division of Mission Research Corporation, and ATMET. RAMS is used for simulating and forecasting meteorological phenomena, and for depicting the results.

      RAMS is primarily a limited area model, and many of its parameterizations have been designed for mesoscale or higher resolution scale grids. There is no lower limit to the domain size or to the mesh cell size of the model’s finite difference grid; microscale phenomena such as tornadoes and boundary layer eddies, as well as sub-microscale turbulent flow over buildings and in a wind tunnel, have been simulated with this code. Two-way interactive grid nesting in RAMS allows local fine mesh grids to resolve smallscale atmospheric systems such as thunderstorms, while simultaneously modeling the large-scale environment of the systems on a coarser grid.

      The atmospheric model is constructed around the full set of nonhydrostatic, compressible equations that atmospheric dynamics and thermodynamics, plus conservation equations for scalar quantities such as water vapor and liquid and ice hydrometeor mixing ratios. These equations are supplemented with a large selection of parameterizations for turbulent diffusion, solar and terrestrial radiation, moist processes including the formation and interaction of clouds and precipitating liquid and ice hydrometeors, kinematic effects of terrain, cumulus convection, and sensible and latent heat exchange between the atmosphere and the surface, which consists of multiple soil layers, vegetation, snow cover, canopy air, and surface water.

      The RAMS User’s Guide is intended as an aid to those who need to install RAMS on a computer system and/or run the model as a tool for studying atmospheric processes. It does not delve into many of the more technical aspects of the code. A separate RAMS Technical Description is available that describes the equations and parameterizations used in the model. A wide range of options is available for the user to select in configuring a model simulation or forecast, many or most of which are inappropriate for a particular application. The main reasons for the availability of options fall into two categories. First, certain options are required for some applications but not for others. For example, the parameterization of cumulus convection is intended for use on coarse grids where convective currents are not resolvable, whereas on fine grids, the model can simulate convection explicitly and cumulus convection should not be parameterized. Second, a variety of options are often made available to allow experimentation and testing of different parameterization schemes or parameter settings, as part of the ongoing research of improving atmospheric models. For research applications, RAMS should not be treated as a black box; as a minimum, it should be used as a “gray box”, requiring considerable knowledge by the user for proper setting of the model flags and parameters. The primary intent of this documentation is to guide the user in setting up and running a model simulation. We have thus frequently injected our own experiences and advice, particularly in describing how to set values of the atmospheric model namelist variables, but it should be remembered that it is far from possible to cover all avenues in such descriptions. Our experience has been that additional direct consultation is frequently required for a user to come up to speed in using RAMS.