OAGRID creates a GEMPAK grid file which can be used in a Barnes objective analysis program. INPUT PARAMETERS GDFILE *Grid file DELTAN *Station spacing DELTAX *X spacing DELTAY *Y spacing GRDAREA *Area covered by grid EXTEND *Points to extend grid DTAAREA *Data area for OA SOURCE *Data source (SN or SF) SNFILE *Sounding data file SFFILE *Surface data file SNPARM *Sounding parameter list SFPARM *Surface parameter list DATTIM *Date/time LEVELS *Vertical levels MAXGRD *Maximum number of grids PROGRAM DESCRIPTION This program allows the user to create a GEMPAK grid file which contains the information required to perform a Barnes objective analysis. The output grids will be evenly spaced latitude/longitude (CED) grids. Three areas used by the objective analysis programs are defined in this program. GRDAREA defines a region for the output grid. The upper right corner specified will be moved toward the lower left in order to align it on a grid point. The second area, defined by EXTEND, is used to extend the grid area outward by some number of grid points. This area is used as a first-pass grid area in the objective analysis. The default EXTEND values are 2,2,2,2. DTAAREA defines the area over which station data will be input to the analysis. Only data within the EXTEND area are used for the second pass. If a value for DTAAREA is not specified, the EXTEND area will be used. If values for the station spacing and grid spacings, DELTAN, DELTAX, and DELTAY, are all specified by the user, they are stored in the grid file for use by the analysis programs. If any of these numbers is 0, a suggested station spacing is computed using the station data from the file specified. This station spacing will be used to compute values for DELTAX and DELTAY. The computed station spacing is the average of the average minimum station spacing and the uniform station spacing. These station spacing values are computed using the stations reporting data for the first DATTIM. The average minimum station spacing is the average of the distances from each station to its closest station. The uniform spacing is the spacing that would be found between stations if they were evenly spaced over the data area. GDCFIL can also be used to create grid files. OAGRID creates only CED grids, but values for the grid spacing and station spacing are estimated from the input surface or upper air file. GDCFIL creates grid files for grids in any projection, but the grid spacing and station spacing must be input directly. EXAMPLES 1. Create a grid file called TEST.GRD. Use the surface temperature data at the latest time from stations in the surface file SURFDAT to compute the station spacing. The grid area is WV; use defaults for the remaining parameters. Create a file which can contain up to 100 grids. GDFILE = test.grd DELTAN = 0. DELTAX = 0. DELTAY = 0. GRDAREA = wv EXTEND = 2;2;2;2 DTAAREA = SOURCE = sf SFFILE = surfdat SFPARM = tmpf DATTIM = last LEVELS = 0 MAXGRD = 100 2. Create a grid file called GRID.GRD with a station spacing of 5, x spacing of 3 and y spacing of 4. The grid area is over PA; the extended grid area should include 1 grid point in each direction; the data area is PA-. GDFILE = grid.grd DELTAN = 5. DELTAX = 3. DELTAY = 4. GRDAREA = pa EXTEND = 1;1;1;1 DTAAREA = pa- ERROR MESSAGES [OAGRID +1] WARNING : This grid is too large for GEMPAK programs. [OAGRID -1] Fatal error initializing TAE. [OAGRID -2] Fatal error reading TAE parameters. [OAGRID -3] ... is invalid for GRDAREA. [OAGRID -4] ... is invalid for DTAAREA. [OAGRID -5] No data file name specified. [OAGRID -6] Parameter input is invalid. [OAGRID -7] Parameter ... cannot be calculated. [OAGRID -8] Invalid value for DELTAX or DELTAY. [OAGRID -9] Too few stations to calculate DELTAN. [OAGRID -10] Source must be set to SN or SF. [OAGRID -11] Station data file is invalid. [OAGRID -12] Invalid time requested. [OAGRID -13] Invalid level requested.