Domains for the meteorology simulations are defined by several primary parameters: number of grid points in each horizontal dimension, grid spacing, center latitude, center longitude, map projection (Mercator, Lambert conformal, or polar stereographic), and number of “nested” domains and their horizontal dimensions. (Some other user-specific parameters are also defined based on the primary parameters, as required.) These parameters are processed by software that is executed only when a new domain location is required. This software, TERRAIN, makes use of high-resolution global terrain and land-use datasets to create “static files” for the domain. The static files currently include values at each grid point for terrain height and land-use specification (e.g., deciduous forest, desert, water). Future releases of TERRAIN with Models-3 may include other time-independent (diurnal and seasonal) and location-specific information. TERRAIN is described by Guo and Chen [1994].

With CMAQ, you can select a (rectangular) domain of any horizontal dimensions, any grid spacing, and most geographical locations. A nesting capability is also available. The number of grid points in the nests is restricted to a multiple of 3, plus 1, if you plan to use a two-way nesting option (discussed in Section 4.6.5). For example, a valid number of grid points for one horizontal dimension can be 100, which is (33 x 3 + 1), or 85, which is (28 x 3 + 1).