OABSFC performs a Barnes objective analysis on surface data. INPUT PARAMETERS SFFILE *Surface data file GDFILE *Grid file SFPARM *Surface parameter list DATTIM *Date/time DTAAREA *Data area for OA GUESS *Guess file^time GAMMA *Convergence parameter SEARCH *Search radius/EXtrapolation NPASS *Number of passes PROGRAM DESCRIPTION OABSFC performs a Barnes objective analysis on surface data. Multiple parameters may be analyzed at the same time. If more than one time is entered, the analyses will be performed sequentially. The input surface file is specified in SFFILE. Two files may be entered by separating the names with a plus, +. The projection and area for the grid are read from the navigation block in the output grid file. The extend grid area, the station spacing and the data subset area are read from the analysis block. The extend area is used to define a larger grid for the first pass, allowing data to be interpolated back to stations outside the final grid area. The average station spacing is used to compute the weighting functions. The data subset area specifies which data will be used in the analysis. If DTAAREA is blank or set to DATA, the data area defined in the analysis block will be used. This is the recommended procedure. However, DTAAREA may be specified in the same way as the AREA parameter used in other programs. This is especially useful to eliminate stations which are known to have bad data. A first-guess field can be used in the analysis. The name of the grid file containing the guess field must be entered in GUESS. In addition, the time to be used to extract the guess field from the file must be entered as the second value in GUESS following a ^. If a guess field is entered, the navigation information in the guess grid file must be identical to that in the output grid file. When a guess field is used, it is inserted into the grid as the zeroth pass. Each pass of the analysis interpolates data from stations to grid points using the weighting function: WTFUNC = EXP [ -DIST ** 2 / WEIGHT ] where: DIST ** 2 = [ ( lat (grid) - lat (stn) ) ** 2 + ( lon (grid) - lon (stn) ) ** 2 * coslsq (grid) ] COSLSQ = COS ( lat (grid) ) ** 2 WEIGHT = 5.051457 * ( DELTAN * 2 / PI ) ** 2 DELTAN = Station spacing read from grid file analysis block Near the poles, an approximate calculation of the distance along a great circle arc is used. GAMMA, the convergence parameter, multiplies the weights for passes after the first pass. GAMMA must be within the range 0 - 1. Any value outside this range will default to a value of .3. If GAMMA is 0, the number of passes will be set to 1. The recommended value for GAMMA is .3. SEARCH is used to control the search radius, which is the maximum distance that a station may be from a grid point to be used in the analysis for that point. The search radius will be set so that stations whose weighting factor would be less than EXP (-SEARCH) will not be used. SEARCH must be in the range 1 - 50. If it is not, a default value of 20 will be used. If a very small value is used, many grid points will not have 3 stations within the search area and will be set to the missing data value. Entering /EX after the SEARCH value allows data extrapolation to assign values to grid points on the periphery of the data region. This will reduce the number of grid points with missing values in data void regions. NPASS controls the number of passes. Valid values are in the range 1 - 5. Note that two passes are STRONGLY RECOMMENDED. EXAMPLES 1. Analyze temperature, dewpoint and the wind components from the latest time in the surface file, SURFDAT. Add the computed grids to the file, TEST.GRD. SFFILE = surfdat GDFILE = test.grd SFPARM = tmpf;dwpf;uwnd;vwnd DATTIM = last DTAAREA = data GUESS = GAMMA = .3 SEARCH = 10 NPASS = 2 2. Repeat the dewpoint analysis setting the convergence parameter to .25 and eliminating the data at stations DCA and BUF. SFPARM = dwpf DTAAREA = data/-@dca;buf GAMMA = .25 3. Repeat the wind analysis using the 24-hour forecast from the model data stored in model.ngm. SFPARM = uwnd;vwnd DTAAREA = data GUESS = model.ngm*f24 ERROR MESSAGES [OABSFC +9] No data from ... will be used. [OABSFC +8] Parameter ... is a character parameter. [OABSFC +7] Parameter ... cannot be computed. [OABSFC +6] WARNING: Area is not DATA area in file. [OABSFC +5] WARNING: The recommended number of passes is 2. [OABSFC +4] ... is invalid for NPASS. It is set to 2. [OABSFC +3] ... is invalid for search. It is set to 20. [OABSFC +2] WARNING: GAMMA is 0. There will be only 1 pass. [OABSFC +1] ... is invalid for GAMMA. It is set to .3. [OABSFC -1] Fatal error initializing TAE. [OABSFC -2] Fatal error reading TAE parameters. [OABSFC -3] Fatal error initializing GEMPLT. [OABSFC -4] Grid size is too large. [OABSFC -5] Not enough buffer space; reduce number of grids. [OABSFC -6] There are too many stations in data subset area. [OABSFC -7] There are too few stations in data subset area. [OABSFC -8] There are no times in the surface file. [OABSFC -9] No valid parameters have been entered. [OABSFC -10] Surface file ... cannot be opened. [OABSFC -11] Time cannot be found in ....