| DSET data_filename | back 
      to top | 
   
    | This entry specifies the filename of the data file being 
        described. If the data and the descriptor file are not in the same directory, 
        then data_filename must include a full path. If a ^ character is 
        placed in front of data_filename, then data_filename is 
        assumed to be relative to the path of the descriptor file. If you are 
        using the ^ character in the DSET entry, then the descriptor file and 
        the data file may be moved to a new directory without changing any entries 
        in the data descriptor file, provided their relative paths remain the 
        same. For example: If the data descriptor file is: /data/wx/grads/sa.ctl
 and the binary data file is:
 /data/wx/grads/sa.dat
 then the data file name in the data descriptor file can be:
 DSET ^sa.dat
 instead of:
 DSET /data/wx/grads/sa.dat
 If data_filename does not include a full path or a ^, then GrADS 
        will only look for data files in the directory where you are running GrADS. 
       GrADS allows you use a single DSET entry to aggregate multiple data files 
        and handle them as if they were one individual file. The individual data 
        files must be identical in all dimensions except time, and the time range 
        of each individual file must be indicated it its filename. To accomplish 
        this, the DSET entry has a substitution template instead of a filename. 
        See the section on Using Templates 
        for a description of all the possible components of the template. Second, 
        the OPTIONS entry must contain the template keyword.
 | 
   
    | CHSUB  t1  t2  string | back 
      to top | 
   
    | (GrADS version 1.9b4) This 
        entry is used with a new option for templating data files that allows 
        for any user-specified string substitution, instead of only date string 
        substitution. This is useful when none of the standard template options 
        match the time ranges in the files you wish to aggregate, or if the files 
        are located on different disks. When you put the %chtemplate 
        in your DSET entry, then you also need to put additional 
        CHSUB entries in 
        the descriptor file. The string will be substituted for%chin the data file name for the time steps beginning with t1 and 
        ending with t2.See the section on Using 
        Templates for examples.
 
 | 
   
    | DTYPE keyword | back 
      to top | 
   
    | The DTYPE entry specifies the type of data being described. 
      There are four options: grib, hdfsds, netcdf, or station. If the data type 
      is none of these, then the DTYPE entry is omitted completely from the descriptor 
      file and GrADS will assume the data type is gridded binary. 
 
         
          | bufr | (GrADS 
            version 1.9) Data file is a BUFR station data file. This data 
            type must be accompanied by the following special entries: XVAR, 
            YVAR, TVAR, STID. 
            Optional special entries are: ZVAR, TOFFVAR. |   
          | grib | Data file is an indexed GRIB (version 1) file. 
            This data type requires a secondary entry in the descriptor file: 
            INDEX. The INDEX entry provides 
            the filename (including the full path or a ^) for the GRIB index file. 
            The index file is created by the gribmap 
            utility. You must run gribmap and 
            create the index file before you can display the GRIB data in GrADS. |  
          | grib2 | (GrADS version 2.0) Data file is an indexed GRIB2 file. This data type requires a secondary entry in the descriptor file: : 
          INDEX. The INDEX entry provides the filename (including the full path or a ^) for the GRIB2 index file. The index file is created by the gribmap utility. You must run grib2map and create the index file before you can display the GRIB2 data in GrADS. |  
          | hdfsds | (GrADS 
            version 1.9) Data file is an HDF Scientific Data Set (SDS). 
            Although HDF-SDS files are self-describing and may be read automatically 
            using the sdfopen/xdfopen commands, this DTYPE gives you the option of overriding the file's 
            own metadata and creating a descriptor file for some or all of the 
            variables in the file. This DTYPE may also be used if the metadata 
            in the HDF-SDS file is insufficient or is not coards-compliant. This 
            data type requires a special entry in the units field of 
            the variable declaration. The undef and unpack entries contain special options for 
            this dtype. |  
          | hdf5_grid | (GrADS version 2.0.a7+) Data file is HDF5 gridded format. The HDF5 format is extremely general and is designed to store a variety of data types. The GrADS interface is only for grids, and requires a complete descriptor file -- there is no sdfopen/xdfopen interface for HDF5. |  
          | netcdf | (GrADS version 1.9) 
            Data file is NetCDF. Although NetCDF files are self-describing and 
            may be read automatically using the sdfopen/xdfopen commands, this DTYPE gives you the option of overriding the file's 
            own metadata and creating a descriptor file for some or all of the 
            variables in the file. This DTYPE may also be used if the metadata 
            in the NetCDF file is insufficient or is not coards-compliant. This 
            data type requires a special entry in the units field of 
            the variable declaration. The undef and unpack entries contain special options for 
            this dtype. |  
          | station | Data file is in GrADS station data format. This 
            data type requires a secondary entry in the descriptor file: STNMAP. 
            The STNMAP entry provides the filename (including the full path or 
            a ^) for the station data map file. The map file is created by the stnmap utility. You must run stnmap and create the map file before you can display the station data in 
            GrADS. |  | 
   
    |  INDEX 
        filename  | back 
      to top | 
   
    | This entry specifies the name of the grib map file. It is 
      required when using the DTYPE grib or grib2 entry to read GRIB formatted data. The file is generated by running the external utility gribmap. or grib2map.      Filenaming conventions are the same as those described for the DSET 
      entry. | 
   
    | STNMAP filename | back 
      to top | 
   
    | This entry specifies the name of the station map file. It 
      is required when using the DTYPE station entry to read 
      GrADS-formatted station data. The file is generated by running the external 
      utility stnmap. Filenaming conventions are 
      the same as those described for the DSET entry. | 
   
    |   TITLE string 
     | back 
      to top | 
   
    | This entry gives brief description of the contents of the 
        data set. String will be included in the output from a query command and it will appear in the directory listing 
        if you are serving this data file with the GrADS-DODS 
        Server (GDS), so it is helpful to put meaningful information in the 
        title field. For GDS use, do not use double quotation marks (") in 
        the title. | 
   
    | UNDEF value <undef_attribute_name> | back 
      to top | 
   
    | This entry specifies the undefined or 
        missing data value. UNDEF is a required entry even if there are 
        no undefined data. GrADS operations and graphics routines will ignore 
        data with this value from this data set. (GrADS version 1.9b4) An optional second 
        argument has been added for data sets of DTYPE netcdf 
        or hdfsds -- it is the name of the attribute that contains the undefined 
        value. This should be used when individual variables in the data file 
        have different undefined values. After data I/O, the missing values in 
        the grid are converted from the variable undef to the file-wide undef 
        (the numerical value in the first argument of the UNDEF record). Then 
        it appears to GrADS that all variables have the same undef value, even 
        if they don't in the original data file. If the data require a transformation 
        using the attributes named in the UNPACK entry, 
        GrADS assumes the variable undef value corresponds to the data values 
        as they appear in the file, i.e., before they are transformed 
        using a scale factor and offset. Missing packed data values are thus assigned 
        the file-wide undef value and are never unpacked. Attribute names are 
        case sensitive, and it is assumed that the name is identical for all variables 
        in the netcdf or hdfsds data file. If the name given does not match any 
        attributes, or if no name is given, the file-wide undef value will be 
        used.
 Example: UNDEF 1e+33 _FillValue
 | 
   
    | UNPACK scale_factor_attribute_name 
      <add_offset_attribute_name> | back 
      to top | 
   
    | (GrADS version 1.9 ) 
        This entry is used with DTYPE  netcdf, hdfsds, or hdf5_grid (GrADS version 2.0.a7+ ) for 
        data variables that are 'packed' -- i.e. non-float data that need to be 
        converted to float by applying the following formula:  
             y = x * scale_factor  + add_offset 
        If your self-describing file does not have an offset attribute, the 2nd argument may 
        be omitted, and the offset will be assigned the default value of 0.0. 
        If your self-describing file has an offset attribute, but not a scale factor, use "NULL" for the scale_factor_attribute_name . (This "NULL" option is in GrADS version 2.0.0+ ). Attribute names are case sensitive, and it is assumed that the names are 
        identical for all variables in the netcdf or hdfsds data file. If the 
        names given do not match any attributes, the scale factor will be assigned 
        a value of 1.0 and the offset will be assigned a value of 0.0. The transformation 
        of packed data is done after the undef test has been applied.  
        Examples:  
        UNPACK scale_factor add_offset 
        UNPACK NULL add_offset 
        UNPACK Slope Intercept
       | 
   
    |   FILEHEADER length 
     | back 
      to top | 
   
    | This optional entry tells GrADS that your data file has a 
      header record of length bytes that precedes the data. GrADS will 
      skip past this header, then treat the remaineder of the file as though it 
      were a normal GrADS binary file after that point. This optional descriptor 
      file entry is only valid for GrADS gridded data sets. | 
   
    |  
	 THEADER lengthHEADERBYTES length<
 | back 
      to top | 
   
    | These two equivalent  optional entries tell GrADS that the data file has a header 
      record of length bytes preceding each time block of binary data. Use one or the other but not both.
      These entries are only valid for GrADS gridded data 
      sets. See the section on structure 
      of a gridded binary data file for more information. | 
  
    | TRAILERBYTES length | back to top | 
  
    | This optional entry tell GrADS that the data file has a trailer record of length bytes following
	 each time block of binary data. This entry is only valid for GrADS gridded data sets. See the section on structure of a gridded binary data file for more information. | 
   
    | XYHEADER length | back 
      to top | 
   
    | This optional entry tells GrADS that the data file has a header 
      record of length bytes preceding each horizontal grid (XY block) of binary 
      data. This entry is only valid for GrADS gridded 
      data sets. See the section on structure of a gridded binary data file 
      for more information. | 
   
    | XVAR x,y | back 
      to top | 
   
    | (GrADS version 1.9) 
      This entry provides the x,y pair for the station's longitude. This entry 
      is required for DTYPE bufr. | 
   
    | YVAR x,y | back 
      to top | 
   
    | (GrADS version 1.9) This entry 
      provides the x,y pair for the station's latitude. This entry is required 
      for DTYPE bufr. | 
   
    | ZVAR x,y | back 
      to top | 
   
    | (GrADS version 1.9) This entry 
      provides the x,y pair for the station data's vertical coordinate (e.g., 
      pressure). This is an optional entry for DTYPE bufr. | 
   
    | STID x,y | back 
      to top | 
   
    | (GrADS version 1.9) This entry 
      provides the x,y pair for the station ID. This entry is required for DTYPE 
      bufr. | 
   
    | TVAR yr x,y 
      mo x,y dy x,y hr x,y mn x,y sc x,y | back 
      to top | 
   
    | (GrADS version 1.9) 
      This entry provides the x,y pairs for all the base time 
      coordinate variables. Each time unit (year=yr, month=mo, day=dy, hour=hr, 
      minute=mn, second=sc) is presented as a 2-letter abbreviation followed by 
      the x,y pair that goes with that time unit. The time for any individual 
      station report is the base time plus the offset time (see TOFFVAR). 
      All six base time units are not required to appear in the TVAR record, only 
      those that are in the data file. This entry is required for DTYPE 
      bufr. | 
   
    | TOFFVAR yr x,y 
      mo x,y dy x,y hr x,y mn x,y sc x,y | back 
      to top | 
   
    | (GrADS version 1.9) 
      This entry provides the x,y pairs for all the offset time 
      coordinate variables. The syntax is the same as TVAR. 
      The time for any individual station report is the base time plus the offset 
      time. All six offset time units are not required to appear in the TOFFVAR 
      record, only those that are in the data file. This is an optional entry 
      for DTYPE bufr. | 
  
    |  CACHESIZE bytes | back 
      to top | 
  
    | (GrADS version 2.0.a8+) 
    This entry overrides the default size of the cache for reading HDF5 or NetCDF4 files. It is not relevant for other data types. It should not be necessary to set the cache size explicitly unless the data file has especially large chunks. Please see the documentation on compression. |  | 
   
    |  OPTIONS keyword | back 
      to top | 
   
    | This entry controls various aspects of the way GrADS interprets 
        the raw data file. It replaces the old FORMAT record. The keyword 
        argument may be one or more of the following: 
        
          | pascals | (GrADS version 2.0) (For DTYPE grib2 only) Indicates that pressure values that appear in the descriptor file (in the ZDEF entry and in the GRIB2 codes in the variable declarations)  are given in units of Pascals. The gribmap utility requires pressure to be given in Pascals. If this keyword is present, the pressure level values will be converted to millibars after the gribmap index is generated and the descriptor file is opened with GrADS. If this keyword is omitted, pressure levels will remain in Pascals, and many of the internal functions (which assume a vertical dimension in units of millibars) will not work properly. |   
          | yrev | Indicates that the Y dimension (latitude) in the data file has been 
            written in the reverse order from what GrADS assumes. An important 
            thing to remember is that GrADS still presents the view that the data 
            goes from south to north. The YDEF statement does not change; it still 
            describes the transformation from a grid space going from south to 
            north. The reversal of the Y axis is done as the data is read from 
            the data file. |   
          | zrev | Indicates that the Z dimension (pressure) in the 
            data file has been written from top to bottom, rather than from bottom 
            to top as GrADS assumes. The same considerations as noted above for 
            yrev also apply. |   
          | template | Indicates that a template for multiple data files is in use. For 
            more information, see the section on Using 
            Templates. |   
          | sequential | Indicates that the file was written in sequential 
            unformatted I/O. This keyword may be used with either station or gridded 
            data. If your gridded data is written in sequential format, then each 
            record must be an X-Y varying grid. If you have only one X and one 
            Y dimension in your file, then each record in the file will be one 
            element long (it may not be a good idea to write the file this way). |   
          | 365_day_calendar | Indicates the data file was created with perpetual 365-day years, 
            with no leap years. This is used for some types of model ouput. |   
          | byteswapped | Indicates the binary data file is in reverse byte 
            order from the normal byte order of your machine. Putting this keyword 
            in the OPTIONS record of the descriptor file tells GrADS to swap the 
            byte order as the data is being read. May be used with gridded or 
            station data. |   
          | The best way to ensure hardware independence 
            for gridded data is to specify the data's source platform. This facilitates 
            moving data files and their descriptor files between machines; the 
            data may be used on any type of hardware without having to worry about 
            byte ordering. The following three OPTIONS keywords are used to describe 
            the byte ordering of a gridded or station data file: |   
          | big_endian | Indicates the data file contains 32-bit IEEE floats 
            created on a big endian platform (e.g., sun, sgi) |   
          | little_endian | Indicates the data file contains 32-bit IEEE floats 
            created on a little endian platform (e.g., iX86, and dec) |   
          | cray_32bit_ieee | Indicates the data file contains 32-bit IEEE floats 
            created on a cray. |  | 
   
    | PDEF | back 
      to top | 
   
    | PDEF is so powerful it has its own documentation 
      page. | 
   
    |  XDEF xnum mapping 
        <additional arguments>  | back 
      to top | 
   
    |  This entry defines the grid point values for the X dimension, 
        or longitude. The first argument, xnum, specifies the number of 
        grid points in the X direction. xnum must be an integer >= 1. mapping 
        defines the method by which longitudes are assigned to X grid points. 
        There are two options for mapping: 
       
        LINEAR    Linear mapping LEVELS    Longitudes specified individually
  The LINEAR mapping method requires two additional arguments: start 
        and increment. start is a floating point value that indicates 
        the longitude at grid point X=1. Negative values indicate western longitudes. 
        increment is the spacing between grid point values, given as a 
        positive floating point value. 
        The LEVELS mapping method requires one additional argument, value-list, 
        which explicitly specifies the longitude value for each grid point. value-list 
        should contain xnum floating point values. It may continue into 
        the next record in the descriptor file, but note that records may not 
        have more than 255 characters. There must be at least 2 levels in value-list; 
        otherwise use the LINEAR method. 
        Here are some examples: 
       
        
           
            | XDEF | 144 | LINEAR | 0.0 2.5 |   
            | XDEF | 72 | LINEAR | 0.0 5.0 |   
            | XDEF | 12 | LEVELS | 0 30 60 90 120 150 180 210 240 270 300 330 |   
            | XDEF | 12 | LEVELS | 15 45 75 105 135 165 195 225 255 285 315 345 |  | 
   
    | YDEF ynum mapping <additional 
      arguments> | back 
      to top | 
   
    | This entry defines the grid point values for the Y dimension, 
      or latitude. The first argument, ynum, specifies the number of grid 
      points in the Y direction. ynum must be an integer >= 1. mapping 
      defines the method by which latitudes are assigned to Y grid points. There 
      are several options for mapping:  
       
        LINEAR    Linear mapping LEVELS    Latitudes specified individually
 GAUST62   Gaussian T62 latitudes
 GAUSR15   Gaussian R15 latitudes
 GAUSR20   Gaussian R20 latitudes
 GAUSR30   Gaussian R30 latitudes
 GAUSR40   Gaussian R40 latitudes
 
  The LINEAR mapping method requires two additional arguments: start 
        and increment. start is a floating point value that indicates 
        the latitude at grid point Y=1. Negative values indicate southern latitides. 
        increment is the spacing between grid point values in the Y direction. 
        It is assumed that the Y dimension values go from south to north, so increment 
        is always positive. 
        The LEVELS mapping method requires one additional argument, value-list, 
        which explicitly specifies the latitude for each grid point, from south 
        to north. value-list should contain ynum floating point 
        values. It may continue into the next record in the descriptor file, but 
        note that records may not have more than 255 characters. There must be 
        at least 2 levels in value-list; otherwise use the LINEAR method. 
        The Gaussian mapping methods require one additional argument: start. 
        This argument indicates the first gaussian grid number. If the data span 
        all latitudes, start would be 1, indicating the southernmost gaussian 
        grid latitude. 
        Here are some examples: 
       
        
           
            | YDEF | 73 | LINEAR | -90 2.5 |   
            | YDEF | 180 | LINEAR | -90 1.0 |   
            | YDEF | 18 | LEVELS | -85 -75 -65 -55 -45 -35 -25 -15 -5 5 15 25 35 45 55 65 75 85 |   
            | YDEF | 94 | GAUST62 | 1 |   
            | YDEF | 20 | GAUSR40 | 15 |   The NCEP/NCAR Reanalysis surface variables are on the GAUST62 grid. 
        The final example shows that there are 20 Y dimension values which start 
        at Gaussian Latitude 15 (64.10 south) on the Gaussian R40 grid | 
   
    | ZDEF znum mapping <additional 
      arguments> | back 
      to top | 
   
    |  This entry defines the grid point values for the Z dimension. 
        The first argument, znum, specifies the number of pressure levels. 
        znum must be an integer >= 1. mapping defines the method 
        by which level values are assigned to Z grid points. There are two options 
        for mapping: 
        The LINEAR mapping method requires two additional arguments: start 
        and increment. start is a floating point value that indicates 
        the level value at grid point Z=1. increment is the spacing between 
        grid point values in the Z direction, or from lower to higher. increment 
        must be non-zero and non0negative. The LEVELS mapping method requires one additional argument, value-list, 
        which explicitly specifies the pressure level for each grid point in ascending 
        order. value-list should contain znum floating point values. 
        It may continue into the next record in the descriptor file, but note 
        that records may not have more than 255 characters.   Here are some examples: 
       
        
           
            | ZDEF | 7 | LEVELS | 1000 850 700 500 300 200 100 |   
            | ZDEF | 17 | LEVELS | 1000 925 850 700 600 500 400 300 250 200 150 100 70 50 |  (GrADS version 2.0) (For DTYPE grib2 only) If your Z axis is pressure, the gribmap utility requires the level values to be given in units of Pascals instead of millibars. Use the "options pascals" keyword to convert the unit of the level values to millibars after the gribmap index is generated and when the descriptor file is opened with GrADS. Pressure level values may remain in Pascals, but then many of the internal functions (which assume a vertical dimension in units of millibars) will not work properly.  | 
  
    | TDEF tnum LINEAR start increment | back to top | 
  
    |  This entry defines the grid point values for the T dimension. The first argument, tnum, specifies the number of time steps. tnum must be an integer >= 1. The method by which times are assigned to T grid points is always LINEAR. 
            start indicates the initial time value at grid point T=1. start must be specified in the GrADS absolute date/time format: 
            where: 
           
            
              
                | hh | = | hour (two digit integer) |  
                | mm | = | minute (two digit integer) |  
                | dd | = | day (one or two digit integer) |  
                | mmm | = | 3-character month |  
                | yyyy | = | year (may be a two or four digit integer; 2 digits implies a year between 1950 and 2049) |  If not specified, hh defaults to 00, mm defaults to 00, and dd defaults to 1. The month and year must be specified. No intervening blanks are allowed in the GrADS absolute date/time format. 
            increment is the spacing between grid point values in the T direction. increment must be specified in the GrADS absolute time increment format: 
            where: 
           
            
              
                | vv | = | an integer number, 1 or 2 digits |  
                | kk | = | mn (minute) hr (hour)
 dy (day)
 mo (month)
 yr (year)
 |   Here are some examples:  
            
              
                | TDEF | 60 | LINEAR | 00Z31dec1999 1mn |  
                | TDEF | 73 | LINEAR | 3jan1989 5dy |  
                | TDEF | 730 | LINEAR | 00z1jan1990 12hr |  
                | TDEF | 12 | LINEAR | 1jan2000 1mo |  
                | TDEF | 365 | LINEAR | 12Z1jan1959 1dy |  
                | TDEF | 40 | LINEAR | 1jan1950 1yr |  | 
  
    | EDEF enum NAMES <list of names> | back to top | 
  
    |  | 
  
    | EDEF enum ensemble_record_1
 ensemble_record_2
 ...
 ensemble_record_enum
 ENDEDEF
 | back to top | 
  
    | (GrADS version 2.0) This entry defines the ensemble dimension. All ensemble members must have identical X, Y, and Z dimensions, the same list of variables, and the same time axis increment. There are two different syntaxes for the EDEF entry: the first  is simpler and requires only the names for each ensemble member, the second expanded form contains a name, individual time axis information, and optional GRIB2 codes. Both EDEF syntaxes begin with the enum argument, an integer >=1 which specifies the number of ensemble members. If all of the ensemble members have an identical time axis (i.e. length, initial time, and increment are the same for each one), then it is only necessary to distinguish the ensembles by their names, and the simplified EDEF syntax with the NAMES keyword may be used. A simple space-delimited list of names is all that is required. Ensemble names must have between 1 and 15 alphanumeric characters, lower case only. (In version 2.0.0 and later, mixed case ensemble names are allowed). Some examples are:  
      
        
          | EDEF | 10 | NAMES | 1 2 3 4 5 6 7 8 9 10 |  
          | EDEF | 12 | NAMES | m01 m02 m03 m04 m05 m06 m07 m08 m09 m10 m11 ensm |  
          | EDEF | 7 | NAMES | e1 e2 e3 e4 e5 e6 e7 |  When the OPTIONS TEMPLATE entry is used with EDEF, the ensemble names are used in the %e substitution template to generate the file name. See Using Templates for more details.  If the ensemble members do not have identical time axes (i.e., their lengths or initial times are not the same), 
	  or if you need to include the GRIB2 codes, then you must use the expanded EDEF syntax: a collection of records framed by EDEF and ENDEDEF. 
	  The format of the ensemble records is as follows:  The ensname is the  1-15 character "name" for the ensemble member. The length is the size of the time axis of the ensemble, which must be less than or equal to the tnum argument in the TDEF entry. (The time axis described by TDEF must span all the ensemble members.) The start  argument is the initial time  of the ensemble member and must be given in GrADS absolute date/time format. (See TDEF for details).  The grib2 codes are required if (1) the DTYPE is grib2 and (2) there is more than one ensemble member (enum > 1). The expanded form of the EDEF entry must be used when grib2 codes are required, even if the length and start times are the same for all members. For GRIB2 ensembles, support currently exists for four different Product Definition Template (PDT) numbers: 1, 2, 11, and 12. These are grouped into two types: individual ensemble forecasts (PDT 1 and 11) or derived forecasts based on all ensemble members (PDT 2 and 12). For individual ensemble forecasts (PDT 1 and 11), two comma-delimited grib2 codes  are required: the ensemble type and perturbation number. For derived forecasts based on all ensemble members (PDT 2 and 12), only one grib2 code is required: the derived forecast. Clarification of all the GRIB2 nomenclature may be found in the documentation at WMO and NCEP. Two examples are given below.  The first example illustrates ensemble members with different lengths and start times:  
  
    
      | TDEF 591 linear 12z09dec1980 12hr |  
      | EDEF 16 |  
      | ensm | 591 | 12z09dec1980 |  
      | m01 | 591 | 12z09dec1980 |  
      | m02 | 589 | 12z10dec1980 |  
      | m03 | 587 | 12z11dec1980 |  
      | m04 | 585 | 12z12dec1980 |  
      | m05 | 583 | 12z13dec1980 |  
      | m06 | 571 | 12z19dec1980 |  
      | m07 | 569 | 12z20dec1980 |  
      | m08 | 567 | 12z21dec1980 |  
      | m09 | 565 | 12z22dec1980 |  
      | m10 | 563 | 12z23dec1980 |  
      | m11 | 549 | 12z30dec1980 |  
      | m12 | 547 | 12z31dec1980 |  
      | m13 | 545 | 12z01jan1981 |  
      | m14 | 543 | 12z02jan1981 |  
      | m15 | 541 | 12z03jan1981 |  
      | ENDEDEF |  The second example illustrates the use of GRIB2 codes: 
  
    
      | TDEF 31 linear 00z24apr2007 12hr |  
      | EDEF 23 |  
      | p01 | 31 | 00z24apr2007 | 3,1 |  
      | p02 | 31 | 00z24apr2007 | 3,2 |  
      | p03 | 31 | 00z24apr2007 | 3,3 |  
      | p04 | 31 | 00z24apr2007 | 3,4 |  
      | p05 | 31 | 00z24apr2007 | 3,5 |  
      | p06 | 31 | 00z24apr2007 | 3,6 |  
      | p07 | 31 | 00z24apr2007 | 3,7 |  
      | p08 | 31 | 00z24apr2007 | 3,8 |  
      | p09 | 31 | 00z24apr2007 | 3,9 |  
      | p10 | 31 | 00z24apr2007 | 3,10 |  
      | p11 | 31 | 00z24apr2007 | 3,11 |  
      | p12 | 31 | 00z24apr2007 | 3,12 |  
      | p13 | 31 | 00z24apr2007 | 3,13 |  
      | p14 | 31 | 00z24apr2007 | 3,14 |  
      | p15 | 31 | 00z24apr2007 | 3,15 |  
      | p16 | 31 | 00z24apr2007 | 3,16 |  
      | p17 | 31 | 00z24apr2007 | 3,17 |  
      | p18 | 31 | 00z24apr2007 | 3,18 |  
      | p19 | 31 | 00z24apr2007 | 3,19 |  
      | p20 | 31 | 00z24apr2007 | 3,20 |  
      | c00 | 31 | 00z24apr2007 | 1,0 |  
      | avg | 31 | 00z24apr2007 | 0 |  
      | spr | 31 | 00z24apr2007 | 2 |  
      | ENDEDEF |  | 
   
    | VECTORPAIRS U-component,V-component | back 
      to top | 
   
    | (GrADS version 1.9b4) This 
        entry is for explicity identifying vector component pairs. This is only 
        necessary if the data are on a native projection other than lat/lon (i.e. 
        you are using PDEF) and if the winds have to be rotated 
        from a grid-relative sense to an Earth-relative sense. (GrADS has to retrieve 
        both the u and v component in order to do the rotation calculation.) Using this entry replaces the old technique of putting 33 (for U) or 
        34 (for V) in the first element of the units field in the variable declaration. 
        The U-component and V-component arguments should be variable 
        names that appear in the VARS list. They are separated 
        by a comma, with no spaces. More than one pair of components may be listed; 
        in this case, the pairs should be separated by a space. For example:  
        VECTORPAIRS  u,v  u10,v10  uflx,vflx  | 
   
    | VARS varnum variable_record_1
 variable_record_2
 ...
 variable_record_varnum
 ENDVARS
 | back 
      to top | 
   
    |  This ensemble of entries describes all the variables contained 
        in the data set. varnum indicates the number of variables in 
        the data set and is therefore also equal to the number of variable records 
        that are listed between the VARS and ENDVARS entries. ENDVARS must be 
        the final line of the Grads data descriptor file. Any blank lines after 
        the ENDVARS statement may cause open to fail! 
        The format of the variable records is as follows: 
       
        varname levs units description                                 (Version 2.0.1 or earlier)varname levs <additional_codes> units description    (Version 2.0.2 or later)
 The syntax of varname and units is different depending 
        on what kind of data format (DTYPE) you are describing. The  <additional_codes> are only necessary for certain types of GRIB2 data sets. Details provided 
        below: 
         
          | varname | This is a 1-15 character "name" or abbreviation for the data variable. 
            varname may contain alphabetic and numeric characters but it 
            must start with an alphabetic character (a-z). |   
          | varname (DTYPE netcdf,  hdfsds, or hdf5_grid)
 | (GrADS version 
            1.9+) For DTYPE netcdf or hdfsds, varname 
            may have a different syntax. This syntax is required when the name of the data variable in the SDF does not conform to the GrADS naming conventions (see below for list of criteria), but it may also be used to shorten or change the variable name to make it easier to work with inside GrADS. The syntax is: 
              SDF_varname=>grads_varname 
             SDF_varname is the name the data variable was given when the SDF 
              file was originally created. For NetCDF files, this name appears 
              in the output from ncdump. It is important that SDF_varname exactly 
              matches the variable name in the data file. SDF_varname may contain 
              uppercase letters and non-alpha-numeric characters.  The classic varname syntax (i.e., when "SDF_varname 
              =>" is omitted) may be used if SDF_varname meets the criteria 
              for GrADS variable names: it must be less than 16 characters, start 
              with an alphabetic character, and cannot contain any upper case 
              letters or non-alpha-numeric characters.  (GrADS version 
            2.0.a3+) If the SDF_varname contains spaces, substitute "~" for each space -- the spaces in the variable name string will be swapped back in later after the descriptor file has been parsed. (GrADS version 2.0.a7+) For dtype hdf5_grid, the SDF_varname may be particularly long since it must contain the names of all the nested groups (separated by "/") to which the data set belongs. For example:
 /HDFEOS/GRIDS/EarthSurfaceReflectanceClimatology/Data~Fields/MonthlySurfaceReflectance=>msr
 |   
          | levs | This is an integer that specifies the number 
              of vertical levels the variable contains. levs may not exceed 
              znum as specified in the ZDEF statement. If levs is 
              0, the variable does not correspond to any vertical level. Surface 
              variables (e.g. sea level pressure) have a levs value of 
              0.  For DTYPE station or bufr, surface variables 
              have a levs value of 0 and upper air variables have a levs 
              value of 1. (Exception to this rule for bufr data: replicated surface 
              variables are given a levs value of 2).  |  
          | levs(DTYPE grib2)
 | (GrADS version 2.0) This is a comma-delimited list of numbers that provide information about the vertical dimension of a variable. The first number in the list is the number of vertical levels the variable contains or zero if the variable doesn't vary in Z. The remaining numbers are the GRIB2 parameters that specify the veritcal level or layer. The levs field may contain up to five comma-delimited numbers:  
              NLEVS,LTYPE,LVAL,LVAL2,LTYPE2
            where 
              
                
                  | NLEVS | = | The number of vertical levels, or 0 if not Z-varying (Required) |  
                  | LTYPE | = | The level type indicator (Required) |  
                  | LVAL | = | The value of the 1st level (Not Required for all level types) |  
                  | LVAL2 | = | The  value of the 2nd level (Only Required for layers between 2 fixed levels) |  
                  | LTYPE2 | = | The level type indicator for the 2nd level (Only required  if different from LTYPE) |  If NLEVS > 0 and is followed only by the LTYPE, the values for LVAL will be determined by the ZDEF entry. If a variable has an NLEVS entry that is > 0 but less than the number of levels declared in the  ZDEF entry, then the values for LVAL will correspond to the first NLEVS values of the Z axis. If LTYPE is 100 (the GRIB2 code for an isobaric surface), the units of LVAL must be Pascals. If the values of LVAL are taken from the ZDEF entry, use OPTIONS  pascals to convert the vertical coordinate  to millibars once the descriptor file is opened with GrADS. Some level types such as "mean sea level" or "tropopause" do not require an LVAL. In this case, LVAL may be omitted (see the "slp" example below). If two LTYPE entries are required but LVAL and LVAL2 are not, then the LVAL entries may be omitted, with adjacent commas used to indicate missing values (see the "cloud" example below).  Examples: 
              
                
                  | hgt | 26,100 | 0,3,5 | Geopotential Height [gpm] |  
                  | hgt500 | 0,100,50000 | 0,3,5 | Geopotential Height at 500mb [gpm] |  
                  | slp | 0,101 | 0,3,1 | Sea Level Pressure [Pa] |  
                  | t2m | 0,103,2 | 0,0,0 | 2-meter Temperature [K] |  
                  | soilt1 | 0,106,0,0.1 | 0,0,0 | Soil Temp, 0-0.10m below surface [K] |  
                  | cloud | 0,1,,,8 | 0,6,1 | Total Cloud Cover, from surface to  TOA [%] |  The external utilities grib2scan and wgrib2 are quite useful in determining what the values for the levs field should be for a GRIB2 data file. |  
          | additional_codes (DTYPE grib2)
 (optional)
 | (GrADS version 2.0.2+) This field specifies any additional GRIB2 codes that are required to uniquely identify the record when the elements in the levs and units fields are not sufficient. It is only required for certain Product Definition Templates: the Probability Forecasts (PDT 5 and 9) and the Optical Properties of Aerosol (PDT 48). The additional_codes field always begins with the letter "a" (for "additional") followed by a set of comma-delimited numbers. The quantity and meaning of the numbers depends on the product. |  
          | additional_codes (PDT 5 or 9)
 | For the Probability Forecasts (PDT 5 or  9), the additional_codes field has 2 or 3 comma-delimted numbers, preceded by the letter "a" :where 
                
                  | PTYPE | = | The probability type indicator |  
                  | LIMIT | = | The value of the limit (for probabilities above or below the given limit) |  
                  | LIMIT2 | = | The  value of the 2nd limit (for probabilities between the 2 given limits) (only needed for PTYPE=2)
 |  Examples: 
                
                  | pt2m273 | 0,103,2 | a0,273 | 0,0,0 | Prob. of 2-m Temp below 273 |  
                  | pcape250 | 0,1,0 | a1,250 | 0,7,6 | Prob. of CAPE above 250 |  
                  | pcape500 | 0,1,0 | a1,500 | 0,7,6 | Prob. of CAPE above 500 |  
                  | pcape1000 | 0,1,0 | a1,1000 | 0,7,6 | Prob. of CAPE above 1000 |  
                  | pcsnow1 | 0,1,0 | a2,1,1 | 0,1,195 | Prob. of categor. snow between 1 and 1 |  The external utilities grib2scan (with the -c option) and wgrib2 are quite useful in determining what the values for the additional_codes field should be for a GRIB2 data file. |  
          | additional_codes (PDT 48)
 | For the Aerosol Forecasts (PDT 48), the  additional_codes field may have up to 7 comma-delimted numbers, preceded by the letter "a": 
   
            whereaATYPE,STYPE,S1,S2,WTYPE,W1,W2 
    
      | ATYPE | = | The aerosol type indicator |  
      | STYPE | = | The type of interval for the first and second size |  
      | S1 | = |  The first size (in meters) |  
      | S2 | = | The second size (in meters) |  
      | WTYPE | = | The type of interval for the first and second wavelength |  
      | W1 | = | The first wavelength (in meters) |  
      | W2 | = | The second wavelength (in meters) |  The ATYPE code is always required. If the STYPE is non-missing, then the trio of numbers STYPE,S1,S2 must be included in the additional_codes field. Similarly, if WTYPE is non-missing, then the trio of numbers WTYPE,W1,W2 must be included in the additional_codes field. If both STYPE and WTYPE are non-missing, then all six codes must be present in the order listed above.  Examples: 
    
      | aotk | 0,10,0 | a62000,0,2e-5,0,7,5.45e-7,5.65e-7 | 0,0,0 | *desc1 |  
      | aemflx | 0,10,0 | a62001,0,2e-05,0 | 0,20,3 | *desc2 |  *desc1=Total Aerosol Optical Thickness,
        size  < 2e-5, 
        wavelength >= 5.45e-7 
        and <= 5.65e-7
 *desc2=Atmosphere Emission Mass Flux
        for Dry Dust, 
        size is < 2e-5
 The external utilities grib2scan (with the -c option) and wgrib2 are quite useful in determining what the values for the additional_codes field should be for a GRIB2 data file.  |   
          | The units component of the variable 
            record is used for data with DTYPE bufr, grib, 
            netcdf, or hdfsds. It is also used for non-standard binary data files 
            that require special "unpacking" instructions, and special 
            cases of pre-projected wind components. If the data you are describing 
            does not fall into any of these categories, put a value of 99 in the 
            units field. |   
          | units | For flat binary files containing 4-byte floating-point data that 
            are not pre-projected, this field is ignored but must be included. 
            Put in a value of 99. |   
          | units (DTYPE bufr)
 | (GrADS version 
            1.9) For DTYPE bufr files, this field 
            contains the x,y pair for the named variable. |   
          | units (DTYPE grib)
 | For DTYPE grib, the units 
              field specifies the GRIB parameters of the variable. This information 
              is used by the gribmap utility for 
              mapping the variables listed in the descriptor file to the data 
              records in the GRIB files. This parameter may contain up to four 
              comma-delimited numbers: 
             
              VV,LTYPE,LVAL,TRI 
                where,or
 VV,LTYPE,LVAL,LVAL2
 
              
                 
                  | VV | = | The GRIB parameter number (Required) |   
                  | LTYPE | = | The level type indicator (Required) |   
                  | LVAL | = | The value of the 1st level  (Required if NLEVS=0) |  
                  | LVAL2 | = | The value of the 2nd level (Optional) |   
                  | TRI | = | The "time range indicator"                    (Optional) |  The external utilities gribscan and 
              wgrib 
              are quite useful in determining what the values for the units 
              field should be for a GRIB data file. Examples: 
              
                 
                  | u | 39 | 33,100 | U Winds [m/s] |   
                  | t | 39 | 11,100 | Temperature [K] |   
                  | ts | 0 | 11,1 | Surface Temperature [K] |   
                  | tb | 0 | 11,116,60,30 | Temperature, 30-60mb above surface [K] |   
                  | dpt | 0 | 17,100,1000 | Dew Point Temperature at 1000 mb [K] |  |  
          | units (DTYPE grib2)
 | (GrADS version 2.0) This is a comma-delimited list of  values that identify  a GRIB2 parameter (variable):  where,  
              
                
                  | DISC | = | The  parameter Discipline (Required) |  
                  | CAT | = | The  parameter Category  (Required) |  
                  | NUM | = | The  parameter Number   (Required) |  
                  | SP | = | The Statistical Process used to derive the parameter (May be required if parameter is not an instantaneous value)
 |  
                  | SP2 | = | The Spatial Process used to interpolate the parameter (Required only for Product Definition Template 4.15)
 |  Some examples are:  
                
                  | u | 26,100 | 0,2,2 | U-Component of Wind [m/s] |  
                  | v | 26,100 | 0,2,3 | V-Component of Wind [m/s] |  
                  | t2max | 0,103,2 | 0,0,5 | 2-meter Temperature Maximum [K] (NCEP) |  
                  | t2max | 0,103,2 | 0,0,0,2 | 2-meter Temperature Maximum [K] (TIGGE) |  
                  | soilm1 | 0,106,0,0.1 | 2,0,192 | Soil Moisture, 0-0.10m below surface [K] |  
                  | catave | 10,100 | 0,19,22,0,3 | Spatial Avg. of Clear Air Turbulence [%] |  
                  | catmax | 10,100 | 0,19,22,2,3 | Spatial Max of Clear Air Turbulence [%] |    |   
          | units (DTYPE netcdf,
 hdfsds, or hdf5_grid)
 | (GrADS 
              version 1.9) For DTYPE netcdf or hdfsds or hdf5_grid (GrADS 
              version 2.0.a7+) , 
              the units field is a comma-delimited list of the varying 
              dimensions of the variable. Dimensions expressed as x, y, z, or 
              t correspond to the four axes defined by XDEF, YDEF, ZDEF and TDEF. 
              For example, a surface variable such as sea level pressure might 
              look like this: 
             
              presSFC=>psfc   0   y,x   Surface 
              Pressure 
             A time-varying atmospheric variable such as geopotential height 
              might look like this: 
              Height=>hght   17   t,z,y,x   Geopotential 
              Height (m) 
             The order of the dimensions listed in the units 
              field does matter. They must describe the shape of the variable 
              as it was written to the SDF data file. For NetCDf files, this information 
              appears in the output from ncdump next to the variable name. 
             If your data file contains a variable that also 
              varies in a non-world-coordinate dimension (e.g. histogram interval, 
              spectral band, ensemble number) then you can put a non-negative 
              integer in the list of varying dimensions that will become the array 
              index of the extra dimension. For example: 
             
               VAR=>hist0   0   0,y,x   
                First historgram interval for VARVAR=>hist1   0   1,y,x   Second 
                historgram interval for VAR
 VAR=>hist2   0   2,y,x   Third 
                histogram interval for VAR
 Another option in this example would be to fill 
              the unused Z axis with the histogram intervals:  
               zdef 3 linear 1 1...
 VAR=>hist   3   z,y,x   VAR Histogram
 In this case, it would appear to GrADS that variable 
              'hist' varies in Z, but the user would have to remember that the 
              Z levels correspond to histogram intervals. The latter technique 
              makes it easier to slice through the data, but is not the most accurate 
              representation. And if you don't have an unsued world-coordinate 
              axis available, then you still have a way to access your data. |   
          | units (non-standard binary)
 | For non-standard binary files, the units field is used 
              to instruct GrADS how to read binary files that do not conform to 
              the default structure 
              or do not contain 4-byte float data. GrADS assumes the data were 
              written in the following order (starting from the fastest varying 
              dimension to the slowest): longitude (X), latitude (Y), vertical 
              level (Z), variable (VAR), time (T). If your binary data set was 
              created or "packed" according to a different dimension sequence, 
              then you can use the units field to tell GrADS exactly how 
              to unpack the data.  For these non-standard binary files, the units field is 
              a series of one or more comma-delimited numbers, the first of which 
              is always -1. The syntax is as follows: 
             There are four options for structure, outlined below. Some 
              of these options have additional attributes which are specified 
              with arg.  
               
                | -1,10,arg | (GrADS 1.9 or earlier) This option indicates that "VAR" and "Z" have 
                    been transposed in the dimension sequence. The order is: longitude 
                    (X), latitude (Y), variable (VAR), vertical level (Z), time(T). 
                    Thus, all variables are written out one level at a time. This feature was designed to be used with NASA GCM data in 
                    the "phoenix" format. The upper air prognostic variables 
                    were transposed, but the diagnostic variables were 
                    not. Thus an arg of 1 means the variable has been var-z 
                    transposed, and an arg of 2 means the variable has 
                    not.  |   
                | -1,20 | This option indicates that "VAR" and "T" have been transposed 
                    in the dimension sequence. The order is: longitude (X), latitude 
                    (Y), vertical level (Z), time(T), variable (VAR). Thus, all 
                    times for one variable are written out in order followed by 
                    all times for the next variable, etc. Data files for which 
					"VAR" and "T" have been transposed may not be templated together. |   
                | -1,30 | (GrADS 1.9 or earlier) This option handles the cruel and unusual case where X and 
                  Y dimensions are transposed and the horizontal grids are (lat,lon) 
                  as opposed to (lon,lat) data. This option causes GrADS to work 
                  very inefficiently. However, it is useful for initial inspection 
                  and debugging. |   
                | -1,40,arg | This option handles non-float data. If there are multiple variables in the same file, they must all be the same type. The dimension sequence is assumed to be the default. The secondary 
                    arg tells GrADS what type of data values are in the 
                    binary file: 
                   
                    units = -1,40,1     = 1-byte unsigned 
                    chars (0-255) units = -1,40,2     = 2-byte unsigned 
                    integers
 units = -1,40,2,-1 = 2-byte signed 
                    integers
 units = -1,40,4     = 4-byte integers
 
 |  |  
          | units (pre-projected wind components)
 | For pre-projected vector component data that require the use of PDEF and rotation, 
            GrADS has to retrieve both the u and v component in order to do the 
            rotation calculation. The new (and recommended) method for matching 
            vector components is to use the VECTORPAIRS descriptor 
            file entry. The old technique (for versions older than 1.9b4) is to 
            use the units field of the variable record. The u-component 
            variable must have a units value of 33, and the v-component 
            variable must have a units value of 34. (This is the GRIB 
            convention). If there are more than one u/v pairs, secondary units values are used. |  
          | description | This is text description or long name for the variable. Max 140 characters. |  
 | 
   
    | @  varname  attribute_type 
       attribute_name  attribute_value | back 
      to top | 
   
    | (GrADS version 1.9b4) To 
        supplement the metadata in your descriptor file, use attribute comments. 
        The first two characters of the attribute comment must be "@" 
        followed by a space -- this distinguishes it from an ordinary comment 
        (see below). Attribute comments may appear anywhere in the descriptor 
        file, and they will be ignored if used with older versions of GrADS.  All file attributes may be retrieved with the 'query 
        attr' command.  varname may be set to "global" to describe general 
        attributes that are valid for the entire data set. Set varname 
        to "lon", "lat", "lev", or "time" 
        to describe attributes of the four coordinate axes; otherwise, use one 
        of the variable names listed in the variable declarations. If a variable 
        name is aliased, use the grads_varname instead of the native SDF_varname. attribute_type should be one of the following case-sensitive 
        types: String, Byte, Int16, UInt16, Int32, UInt32, Float32, Float64. attribute_name may be any single word or string with no spaces 
        (e.g.: "units", "minimum_value") attribute_value can be any string as long as the length of the 
        entire entry does not exceed 512 characters.  For example:@ precip String units mm/day
 @ global String documentation http://put.your.documentation.url.here
 
 
 | 
   
    | * comment | back 
      to top | 
   
    | You may put comments in your descriptor file by beginning 
      the entry with * . Use @ for formatted attribute comments (see above). | 
   
    |  |