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So far we've used SFLIST and SNLIST to list surface and sounding (upper air) data. Now we'd like to look at gridded data. Can you guess what program we'll use? The answer is GDLIST. GDLIST is analogous to SFLIST and SNLIST.
Let's start up the program and read in the defaults file:
prompt% gdlist Creating process: gplt for queue 1 GDATTIM Grid date/time first GLEVEL Grid level 500 GVCORD Grid vertical coordinate PRES GFUNC Grid function tmpc GDFILE Grid file $GEMPAK/data/hrcbob.grd GAREA Graphics area -90;-180;90;180 PROJ Map projection/angles/margins ced SCALE Scaling factor 999 OUTPUT Output device (TPF) t Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, OUTPUT. GEMPAK-GDLIST>restore defaults/gdlist.nts GEMPAK-GDLIST>dis GDATTIM Grid date/time GLEVEL Grid level 500 GVCORD Grid vertical coordinate pres GFUNC Grid function GDFILE Grid file GAREA Graphics area PROJ Map projection/angles/margins mer SCALE Scaling factor 999 OUTPUT Output device (TPF) t GEMPAK-GDLIST>Note the first message that appears after starting up the program:
Creating process: gplt for queue 1This is the first time we've seen the GPLT process. For a description of the multiple processes used by GEMPAK, see the Introduction to GEMPAK chapter. For now we'll ignore this, but be warned, we will discuss it later.
Before we go too much further, remember that we could learn all about the GDLIST program and it's variables by reading on-line help. For now, let's just keep going.
These variable names are virtually the same as the surface and sounding program variables. Note, however, that most start with "G". This is because GEMPAK distinquishes between gridded data variables and non-gridded data variables. As a result, GEMPAK stores the settings separately in the gemglb.nts and last.nts files. This may not make sense now, but later when you aren't using the defaults files as often, you will appreciate the separation.
GDATTIM Analogous to DATTIM (with new features for model data) GLEVEL Analogous to LEVELS GVCORD Analogous to VCOORD GFUNC Analogous to SFPARM and SNPARM GDFILE Analogous to SFFILE, and SNFILE
Don't worry too much about these new variables now. They will be explained in much more detail later.
PROJ --Projection of map/grid --more important for mapping programs --used here (with GAREA) to define subset of grid points to list SCALE --used as scale factor for data --default value of 999 will scale if appropriate GAREA --defines the graphics area --for now, treat this as analogous to AREA; we'll discuss it more later
Practice EXERCISES!!
Print the grid point values of the 500mb heights (HGHT) from the Hurricane Bob gridded data set over the Denver area for the 0 hour forecast of the 0 UTC model run on August 19, 1991.
GEMPAK-GDLIST>gdattim=910819/0000F00
GEMPAK-GDLIST>gfunc=hght
GEMPAK-GDLIST>gdfile=$GEMPAK/data/hrcbob.grd
GEMPAK-GDLIST>garea=den
GEMPAK-GDLIST>dis
GDATTIM Grid date/time 910819/0000F00
GLEVEL Grid level 500
GVCORD Grid vertical coordinate pres
GFUNC Grid function hght
GDFILE Grid file $GEMPAK/data/hrcbob.grd
GAREA Graphics area den
PROJ Map projection/angles/margins mer
SCALE Scaling factor 999
OUTPUT Output device (TPF) t
GEMPAK-GDLIST> run
GDLIST PARAMETERS:
Grid file: $GEMPAK/data/hrcbob.grd
GRID IDENTIFIER:
TIME1 TIME2 LEVL1 LEVL2 VCORD PARM
910819/0000F000 500 PRES HGHT
GAREA: den
SCALE FACTOR : 10** 0
OUTPUT: TERM/
MINIMUM AND MAXIMUM VALUES 5767.83 5921.67
Enter <CR> to accept parameters or type EXIT:
Go ahead and hit return to accept the parameters:
Enter <CR> to accept parameters or type EXIT: Grid file: $GEMPAK/data/hrcbob.grd GRID IDENTIFIER: TIME1 TIME2 LEVL1 LEVL2 VCORD PARM 910819/0000F000 500 PRES HGHT AREA: den GRID SIZE: 53 45 COLUMNS: 23 31 ROWS: 17 23 Scale factor: 10** 0 COLUMN: 23 24 25 26 27 28 29 30 31 ROW 23 5892.11 5892.33 5891.77 5887.50 5876.70 5865.70 5848.47 5810.33 5767.83 ROW 22 5895.80 5899.64 5902.44 5896.98 5886.62 5874.58 5863.39 5839.28 5805.27 ROW 21 5895.47 5901.53 5909.19 5907.61 5901.22 5887.58 5874.11 5858.11 5835.34 ROW 20 5892.52 5896.52 5907.27 5911.47 5908.67 5899.42 5886.67 5874.31 5860.22 ROW 19 5896.33 5901.67 5911.39 5915.92 5916.08 5911.56 5902.61 5891.00 5877.03 ROW 18 5895.77 5903.86 5911.67 5915.73 5918.02 5915.75 5912.05 5905.41 5892.53 ROW 17 5903.83 5909.50 5914.00 5918.50 5921.67 5921.41 5919.20 5913.98 5906.34 Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, OUTPUT. GEMPAK-GDLIST>
Fascinating, eh?Looking at individual grid point values may be a little tedious. Usually, contours, streamlines, or vector displays are used to view gridded data.
Occasionally you might find this program useful in looking for suspect grid point values, or if you want to modify the grid point values in some way. In that case you may want to write out the grid, modify it, and then read it back in to GEMPAK format. You can write out a grid to a file, rather than the screen, by setting:
OUTPUT=f/file.name
where file.name is the name of the file that the grid will be
written to. After making your changes (for example changing a suspect point
to the missing data value, or changing some values to test their affect on
the subsequent analyses), you can read the grid back into a GEMPAK data file
using the program GDEDIT.Even with this in mind, you probably won't be using this program as often as many of the others. However, there is a useful listing program for gridded data files. It is called GDINFO, and we'll discuss it next.
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