WRF - Developmental Testbed Center

V -DX- H| / |DY dx DY| / |H - DX- VThe horizontal grid resolution is taken to be the shortest distance between two mass (H)points (diagonal – dx), while DX and DY refer to distances between adjacent H and Vpoints. The distance between the H points in the diagram above is the hypotenuse of thetriangle with legs DX and DY. Assuming 111 km/degree (a reasonable assumption forthe rotated latitude-longitude grid) the grid spacing in km is approximately equal to:111.0 * (SQRT (DX**2 + DY**2)).12. MAP_PROJ : A character string specifying the projection of the simulation domain.For ARW, accepted projections are 'lambert', 'polar', 'mercator', and 'lat-lon';for NMM, a projection of 'rotated_ll' must be specified. Default value is 'lambert'.13. REF_LAT : A real value specifying the latitude part of a (latitude, longitude) locationwhose (i,j) location in the simulation domain is known. For ARW, ref_lat gives thelatitude of the center-point of the coarse domain by default (i.e., when ref_x and ref_yare not specified). For NMM, ref_lat always gives the latitude to which the origin isrotated. No default value.14. REF_LON : A real value specifying the longitude part of a (latitude, longitude)location whose (i, j) location in the simulation domain is known. For ARW, ref_longives the longitude of the center-point of the coarse domain by default (i.e., when ref_xand ref_y are not specified). For NMM, ref_lon always gives the longitude to whichthe origin is rotated. For both ARW and NMM, west longitudes are negative, and thevalue of ref_lon should be in the range [-180, 180]. No default value.15. REF_X : A real value specifying the i part of an (i, j) location whose (latitude,longitude) location in the simulation domain is known. The (i, j) location is always givenwith respect to the mass-staggered grid, whose dimensions are one less than thedimensions of the unstaggered grid. Default value is (((E_WE-1.)+1.)/2.) = (E_WE/2.).16. REF_Y : A real value specifying the j part of an (i, j) location whose (latitude,longitude) location in the simulation domain is known. The (i, j) location is always givenwith respect to the mass-staggered grid, whose dimensions are one less than thedimensions of the unstaggered grid. Default value is (((E_SN-1.)+1.)/2.) = (E_SN/2.).17. TRUELAT1 : A real value specifying, for ARW, the first true latitude for theLambert conformal projection, or the only true latitude for the Mercator and polarstereographic projections. For NMM, truelat1 is ignored. No default value.WRF-NMM V3: User’s Guide 3-35