WRF - Developmental Testbed Center

mass and wind quantities, but the phantom column does not impact the integration. In thisexample, the x-dimension of the computational grid is 4, wheras the y-dimension is 5.Bydefinition, e_we and e_sn are one plus the computational grid, such that, for this example,e_we=5 and e_sn=6. Note, also, that the number of computational rows must be odd, sothe value for e_sn must always be EVEN.9. GEOG_DATA_RES : A list of MAX_DOM character strings specifying, for each nest,a corresponding resolution or list of resolutions separated by + symbols of source data tobe used when interpolating static terrestrial data to the nest’s grid. For each nest, thisstring should contain a resolution matching a string preceding a colon in a rel_path orabs_path specification (see the description of GEOGRID.TBL options) in theGEOGRID.TBL file for each field. If a resolution in the string does not match any suchstring in a rel_path or abs_path specification for a field in GEOGRID.TBL, a defaultresolution of data for that field, if one is specified, will be used. If multiple resolutionsmatch, the first resolution to match a string in a rel_path or abs_path specification inthe GEOGRID.TBL file will be used. Default value is 'default'.10. DX : A real value specifying the grid distance in the x-direction where the map scalefactor is 1. For ARW, the grid distance is in meters for the 'polar', 'lambert', and'mercator' projection, and in degrees longitude for the 'lat-lon' projection; forNMM, the grid distance is in degrees longitude. Grid distances for nests are determinedrecursively based on values specified for parent_grid_ratio and parent_id. Nodefault value.11. DY : A real value specifying the nominal grid distance in the y-direction where themap scale factor is 1. For ARW, the grid distance is in meters for the 'polar','lambert', and 'mercator' projection, and in degrees latitude for the 'lat-lon'projection; for NMM, the grid distance is in degrees latitude. Grid distances for nests aredetermined recursively based on values specified for parent_grid_ratio andparent_id. No default value.Note: For the rotated latitude-longitude grid used by WRF-NMM, the grid center is theequator. DX and DY are constant within this rotated grid framework. However, in a trueEarth sense, the grid spacing in kilometers varies slightly between the center latitude andthe northern and southern edges due to convergence of meridians away from the equator.This behavior is more notable for domains covering a wide range of latitudes. Typically,DX is set to be slightly larger than DY to counter the effect of meridional convergence,and keep the unrotated, "true earth" grid spacing more uniform over the entire grid.The relationship between the fraction of a degree specification for the E-grid and themore typical grid spacing specified in kilometers for other grids can be approximated byconsidering the following schematic:WRF-NMM V3: User’s Guide 3-34