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GEMPAK / N-AWIPSNEXRAD Composite Tutorial |
NEXRAD ^SDUS[2357]. .... ([0-3][0-9])([0-2][0-9])([0-6][0-9]).*/p(...)(...) FILE -close data/gempak/nexrad/NIDS/\5/\4/\4_(\1:yyyy)(\1:mm)\1_\2\3
The following file name template is used in $GEMTBL/config/datatype.tbl
to define the naming convention which matches the above LDM pattern/action:
NEXRIII $RAD/NIDS/%SITE%/%PROD% %PROD%_YYYYMMDD_HHNN CAT_NIL SCAT_NIL 10 2880 -1
If you use the suggested LDM pattern action above, then you will not have to make any modifications to the supplied template.
GDRADR also uses a station table (default is nexrad.tbl) to determine what radar locations to use for the composite. Each radar location found in the station table will be substituted for the %SITE% template above. The station ID's found in the nexrad,tbl file match the 3 letter ID's used in the PIL pattern shown in the pqact.conf example above. If you are creating a regional composite, you can substantially speed up the gridding process by creating a station table consisting only of those radar locations which will be in the grid domain.
The GFUNC (eg n0r, ntp etc.) defined in GDRADR will be used as the %PROD%. The PIL tag used in the data broadcast identifies each radar product, and is used in the pqact.conf pattern/action line shown above. Each radar file matching the above template will be used in the composite grid product. Upon completion, the gridded data file will contain a grid identified by GFUNC with vertical coordinate NONE and grid level 0.
The output grid file will be created if it does not already exist. The file may be specified in several ways.
RADTIM determines the output grid time for the radar composite. The value of RADTIM may either be 'current', or a GEMPAK dattim. If 'current' is selected for RADTIM, then the current system clock time is used. No data files later than RADTIM will be included in the composite. RADDUR provides the time window previous to RADTIM in order to include data for each site. The time closest to RADTIM will be used. A default RADDUR of 30 minutes is used if RADDUR is blank.
RADFRQ is the frequency in minutes at which the program will run. When RADFRQ is defined, GDRADR will wait for the specified time before rerunning. This option is most useful when RADTIM is set to 'current'. When the program is sleeping, ctrl-c can be used to exit the loop and return to the dynamic tutor. If RADFRQ is not set, the dynamic tutor will be re-entered at the end of processing the radar mosaic.
For more information and examples, see the online help for GDRADR
Using radar data in grid calculations
Here is a script which shows how to determine the 5 most
Interesting radar sites using the
gridded national mosaic from the above script. This script
produces the sample page of sites
here.
The following script shows how to use RUC boundary layer temperature grids
to estimate the precipitation type using masking functions.
The RUC grids are interpolated to the same projection and resolution as
the national radar mosaic
grids shown above. The temperature
grids are then used to create MASK values for the radar reflectivities for
rain, frozen precip, and snow.
Decoding National and Regional Composites from FNEXRAD data feed
The following pqact.conf pattern action lines provide an example for
processing the data into GEMPAK grid files.
#
# National radar composite
FNEXRAD ^radar_mosaic_national
PIPE -close decoders/dcgrib2 -d data/gempak/logs/dcgrib_radar.log
-e GEMTBL=/home/gempak/NAWIPS/gempak/tables
data/gempak/radar/YYYYMMDD_radr.gem
#
# Regional/Floater radar composite
FNEXRAD ^radar_mosaic_regional_(.*) !.*!
PIPE -close decoders/dcgrib2 -d data/gempak/logs/dcgrib_radar.log
-e GEMTBL=/home/gempak/NAWIPS/gempak/tables
data/gempak/radar/YYYYMMDD_float_\1.gem
Any site running GEMPAK 5.6.D or later has the necessary configurations
for decoding and displaying the data in NMAP2 and/or gdplot2. If you are
running an older version of GEMPAK, then you will need to create a
file $GEMTBL/grid/ncargrib2.tbl table which
identifies parameter #201 as N0R from the NCAR model center ID.
If you wish to use other software to decode/view the products, then the relavant GRIB decoding information you will need is that the center identification in the PDS block is "60" which is designates NCAR/UCAR, and the parameter number for the grids will be #201 for level 0 reflectivity.
The $GEMTBL/config/datatype.tbl template file provides the templates of NEXR, NEXF, and NEXL for the national, floater and local region mosaics respectively:
NEXR $GEMDATA/radar YYYYMMDD_radr.gem ............ etc. NEXF $GEMDATA/radar YYYYMMDD_float_* ............ etc. NEXL $GEMDATA/radar YYYYMMDD_local.gem ........... etc.These NEXR and NEXF templates match the decoding example above. The NEXL is designed for sites that locally generate regional mosaics.
The $GEMTBL/nmap/mod_res.tbl file provides for 2 predefined products:
You may want to add "nexf" to the "nexr;nexl" list for these products if you will be decoding the regional floater composite.
The difference between the two products above is that Radar_Reflectivity uses a gdplot2 TYPE=Z and Radar_Reflectivity_qc uses a gdplot2 TYPE=F. The former just fills in the grid boxes. The latter contours the data for a slightly smoother appearance.
If you are looking for an example of plotting the data in gdplot2, use the restore files mentioned in the mod_res.tbl entry as a guide and consult the GDRADR page for examples of how to use the grids in grid calculations, precipitation type plots, etc.
The NMAP2 GRID selection menu will display the available files that match the file templates NEXR, NEXL and NEXF. For floater mosaics, the region of the mosaic will also appear in the pull down allowing for identification when more than 1 region is present (eg, the floater region has been changed during the day).
