SNMOD moves selected sounding data from an input sounding file to
an output sounding file.


INPUT PARAMETERS
 
    SNFILE    Sounding data file
    SNOUTF    Output sounding file
    SNPARM    Sounding parameter list
    AREA      Data area
    DATTIM    Date/time
    LEVELS    Vertical levels
    VCOORD    Vertical coordinate type
    TIMSTN    Times/additional stations
    MRGDAT    Merge data file flag/part type
    IDNTYP    STNM or STID
 
 
PROGRAM DESCRIPTION
 
    SNMOD takes data from a GEMPAK sounding file, SNFILE, and
    writes it to an output GEMPAK sounding file, SNOUTF.
    This program can be used to subset the original dataset
    by time and/or stations and to change the levels and
    vertical coordinate.

    The output dataset may be either a merged or unmerged data
    set.  If the output file does not exist, a new file will be
    created by this program.  If a new file is created, MRGDAT
    will determine whether the output file will be a merged or
    unmerged dataset.  Note that an error will result if the
    input dataset is merged and the output dataset is unmerged.

    The value of SNPARM will be ignored if the output dataset is
    unmerged.  If a merged data file is to be created, SNPARM
    will specify the parameters to be included.  In this case,
    if SNPARM = DSET, the parameters in the input dataset will be
    used.  If the output file is an existing merged dataset, the
    parameters specified in SNPARM must be in the dataset.  In
    this case, if SNPARM = DSET, the parameters in the output file
    will be used.  Undecoded text (raw reports) may be included in
    the input file, but will not be moved to the output file.

    If the output file is to be created, the maximum number of
    times and stations which can be stored in the file must be
    specified in TIMSTN.

    IDNTYP has been added to specify whether station numbers or
    station identifiers will be used in referring to stations.
    Generally, IDNTYP should be set to STNM to use station
    numbers.  However, in datasets which do not have station
    numbers, or which have a single invalid number, character
    station identifiers must be used and IDNTYP must be set
    to STID.


EXAMPLES
 
    1.  Put the mandatory data for stations in an area centered
        on IL at time 910819/1200 into a new unmerged sounding
        file, NEW.SND, which may contain 2 times and 150
        stations.

        SNFILE  =  gemdata:hrcbob.snd
        SNOUTF  =  new.snd
        SNPARM  =  dset
        AREA    =  il
        DATTIM  =  19/12
        LEVELS  =  man
        VCOORD  =  pres
        TIMSTN  =  2/150
        MRGDAT  =  no
        IDNTYP  =  stnm

    2.  Add the stations at time 910819/00 to the file created in
        example 1.

        DATTIM  =  19/00

    3.  Create an isentropic dataset containing the specified
        parameters with levels every 5 degrees.  Include all the
        US stations.

        SNFILE  =  gemdata:hrcbob.snd
        SNOUTF  =  thta.snd
        SNPARM  =  thta;pres;mixr;uwnd;vwnd;psym
        AREA    =  @us
        DATTIM  =  all
        LEVELS  =  250-450-5
        VCOORD  =  thta
        TIMSTN  =  4/150
        MRGDAT	=  yes

ERROR MESSAGES
 
    [SNMOD  -1]     Fatal error initializing TAE.
    [SNMOD  -2]     Fatal error reading TAE parameters.
    [SNMOD  -3]     Output file cannot be unmerged type.
    [SNMOD  -4]     A new file cannot be created with no times.
    [SNMOD  -5]     A new file cannot be created with no stations.
    [SNMOD  -6]     Parameter ... cannot be computed.
    [SNMOD  -7]     ... is character type; cannot be added to file.
    [SNMOD  -8]     Output vertical coordinate ... cannot be used.
    [SNMOD  -9]     No valid parameters were specified.
    [SNMOD -10]     Time ... cannot be added to the output file.
    [SNMOD -11]     Station ... cannot be added to output file.
    [SNMOD -12]     Parms do not match those in output data set.
    [SNMOD -13]     Output file name is blank.