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Clint, This is the quick answer... You are right in that the display of MIXR is scaled by 1000 to produce g/kg (see $GEMPAK/source/gemlib/dg/dgscal.f). Calculations are done in the dimensionless MKS units. However, once you perform a calculation on the data (in MKS units), and store the output for a different name (other than the recognized MIXR name), your display will not be scaled to g/kg. So, you will have to take that into acount when you SCALE the output for display. I believe that is the gist of your message below. That is, when you specify GRDNAM as MIXR_MOD for copying the data, the display output will not be scaled to g/kg as MIXR would. You may also notice some small roundoff changes due to the packing (PACK=grib/16) if the original data used more precision. If you want me to look into a specific calculation and how to carry forth the MKS units let me know. Chiz Steve Chiswell Unidata User Support >From: Clint Rowe <address@hidden> >Organization: UCAR/Unidata >Keywords: 200201081709.g08H91N04033 >Chiz, > >I'm finding some strange behavior when trying to do some grid computations >in gempak. I'm trying to compare two MM5 model runs and am creating a three- >panel display (the two fields and their difference) using version 5.6e. I've >written a script that does this for whatever field I'm interested in. >Everything seemed to be working okay until Mark noticed that when plotting >2m mixing ratios, the difference map were all blank, even though there are >noticable differences in the two model runs. If I run GDLIST on the two >files and look at mixr, mixr+2 and sub(mixr, mixr+2), I get strange results. >The reported mins and maxs look okay for the two runs and show differences >as seen in the plots. However, the results of the subtraction seems to >yield zeros across the entire domain (i.e., the min and max are both zero). > > >papagayo% gdlist > GDATTIM Grid date/time 860731/1200 > GLEVEL Grid level 2 > GVCORD Grid vertical coordinate zagl > GFUNC Scalar grid mixrdiff > GDFILE Grid file test.gem > GAREA Graphics area dset > PROJ Map projection/angles/margins|dr MER > SCALE Scalar scale / vector scale 0 > OUTPUT Output device/filename T > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > >GEMPAK-GDLIST>gdfil=../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/198607 > 31 >00/1986073100_mm5_domain3.gem > GEMPAK-GDLIST>gfunc=mixr > GEMPAK-GDLIST>r > > > GDLIST PARAMETERS: > > Grid file: >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXR > > GAREA: dset > SCALE FACTOR : 10** 0 > OUTPUT: TERM/ > > MINIMUM AND MAXIMUM VALUES 5.58 13.44 >Enter <cr> to accept parameters or type EXIT:ex > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>gfun=mixr+2 > GEMPAK-GDLIST>r > > > GDLIST PARAMETERS: > > Grid file: >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXR > > GAREA: dset > SCALE FACTOR : 10** 0 > OUTPUT: TERM/ > > MINIMUM AND MAXIMUM VALUES 5.52 13.43 >Enter <cr> to accept parameters or type EXIT:ex > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>gfun=sub(mixr,mixr+2) > GEMPAK-GDLIST>r > > > GDLIST PARAMETERS: > > Grid file: >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL SUBMIXR > > GAREA: dset > SCALE FACTOR : 10** 0 > OUTPUT: TERM/ > > MINIMUM AND MAXIMUM VALUES 0.00 0.00 >Enter <cr> to accept parameters or type EXIT:ex > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>ex >papagayo% > > >Okay, so if that wasn't a big enough problem, when I started putting together >something to send you, I found even more strangeness. I copied the mixing >ratio fields from the two files into a new file that I could send to you. I >also calculated the deifference to add to that file. Then, when I began to >check my efforts, I found that the grids I had copied were different than >what I expected. The raw fields had been multipled by 1000 and now there are >small differences (but smaller than implied by the fields themselves). > > >papagayo% gdcfil > GDOUTF Output grid file test.gem > PROJ Map projection/angles/margins|dr MER > GRDAREA Area covered by grid > KXKY Number of grid points in x;y 10;10 > MAXGRD Maximum number of grids 200 > CPYFIL Grid file whose navigation is to >../CTL/1986073100/1986073100_mm5_domain3.gem > ANLYSS Grid analysis block 4/2;2;2;2 > Parameters requested: GDOUTF,PROJ,GRDAREA,KXKY,MAXGRD,CPYFIL,ANLYSS. > GEMPAK-GDCFIL>r > > GDCFIL PARAMETERS: > > New grid file: test.gem > > File copied: ../CTL/1986073100/1986073100_mm5_domain3.gem > > Grid projection: LCC > Lower left corner: 40.51 -104.66 > Upper right corner: 43.65 -96.77 > KX, KY: 156 90 > DELTAN = 4.000 EXTEND = 2; 2; 2; 2 > Maximum number of grids that can be added to file 200 >Enter <cr> to accept parameters or type EXIT: > Parameters requested: GDOUTF,PROJ,GRDAREA,KXKY,MAXGRD,CPYFIL,ANLYSS. > GEMPAK-GDCFIL>ex >papagayo% gddiag > GDFILE Grid file >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > GDOUTF Output grid file test.gem > GFUNC Scalar grid sub(mixr,mixr+2) > GDATTIM Grid date/time 860731/1200 > GLEVEL Grid level 2 > GVCORD Grid vertical coordinate zagl > GRDNAM Grid parameter name mixr_mod > GPACK Packing type/number of bits grib/16 > Parameters requested: GDFILE,GDOUTF,GFUNC,GDATTIM,GLEVEL,GVCORD,GRDNAM, > GPACK. > GEMPAK-GDDIAG>gfunc=mixr+2 > GEMPAK-GDDIAG>r > > > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXR_MOD >Enter a new grid parameter name, <cr> to accept or type EXIT: > Parameters requested: GDFILE,GDOUTF,GFUNC,GDATTIM,GLEVEL,GVCORD,GRDNAM, > GPACK. > GEMPAK-GDDIAG>gfunc=mixr > GEMPAK-GDDIAG>grdnam=mixr_ctl > GEMPAK-GDDIAG>r > > > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXR_CTL >Enter a new grid parameter name, <cr> to accept or type EXIT: > Parameters requested: GDFILE,GDOUTF,GFUNC,GDATTIM,GLEVEL,GVCORD,GRDNAM, > GPACK. > GEMPAK-GDDIAG>l > GDFILE = >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > GDOUTF = test.gem > GFUNC = mixr > GDATTIM = 860731/1200 > GLEVEL = 2 > GVCORD = zagl > GRDNAM = mixr_ctl > GPACK = none > GEMPAK-GDDIAG>gfunc=sub(mixr,mixr+2) > GEMPAK-GDDIAG>l > GDFILE = >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > GDOUTF = test.gem > GFUNC = sub(mixr,mixr+2) > GDATTIM = 860731/1200 > GLEVEL = 2 > GVCORD = zagl > GRDNAM = mixr_ctl > GPACK = none > GEMPAK-GDDIAG>grdnam=mixrdiff > GEMPAK-GDDIAG>r > > > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXRDIFF >Enter a new grid parameter name, <cr> to accept or type EXIT: > Parameters requested: GDFILE,GDOUTF,GFUNC,GDATTIM,GLEVEL,GVCORD,GRDNAM, > GPACK. > GEMPAK-GDDIAG>ex >papagayo% >papagayo% gdinfo > GDFILE Grid file >../CTL/1986073100/1986073100_mm5_domain3.gem+../MOD/1986073100/1986073100_mm5_ > do >main3.gem > LSTALL Full list flag YES > OUTPUT Output device/filename T > GDATTIM Grid date/time 860731/1200 > GLEVEL Grid level 2 > GVCORD Grid vertical coordinate zagl > GFUNC Scalar grid sub(mixr,mixr+2) > Parameters requested: GDFILE,LSTALL,OUTPUT,GDATTIM,GLEVEL,GVCORD,GFUNC. > GEMPAK-GDINFO>gdfil=test.gem > GEMPAK-GDINFO>gfunc=all > GEMPAK-GDINFO>r > > GRID FILE: test.gem > > > GRID NAVIGATION: > PROJECTION: LCC > ANGLES: 30.0 -103.0 60.0 > GRID SIZE: 156 90 > LL CORNER: 40.51 -104.66 > UR CORNER: 43.65 -96.77 > > GRID ANALYSIS BLOCK: > ANALYSIS TYPE: BARNES > DELTAN: 4.000 > DELTAX: -9999.000 > DELTAY: -9999.000 > GRID AREA: 39.00 -106.00 45.00 -96.00 > EXTEND AREA: 39.00 -106.00 45.00 -96.00 > DATA AREA: 39.00 -106.00 45.00 -96.00 > > Number of grids in file: 3 > > Maximum number of grids in file: 200 > > NUM TIME1 TIME2 LEVL1 LEVL2 VCORD PARM > 1 860731/1200 2 ZAGL MIXR_MOD > 2 860731/1200 2 ZAGL MIXR_CTL > 3 860731/1200 2 ZAGL MIXRDIFF > Parameters requested: GDFILE,LSTALL,OUTPUT,GDATTIM,GLEVEL,GVCORD,GFUNC. > GEMPAK-GDINFO>ex >papagayo% gdlist > GDATTIM Grid date/time 860731/1200 > GLEVEL Grid level 2 > GVCORD Grid vertical coordinate zagl > GFUNC Scalar grid all > GDFILE Grid file test.gem > GAREA Graphics area dset > PROJ Map projection/angles/margins|dr MER > SCALE Scalar scale / vector scale 999 > OUTPUT Output device/filename T > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>gfun=mixr_ctl > GEMPAK-GDLIST>scal=0 > GEMPAK-GDLIST>r > > > GDLIST PARAMETERS: > > Grid file: test.gem > > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXR_CTL > > GAREA: dset > SCALE FACTOR : 10** 0 > OUTPUT: TERM/ > > MINIMUM AND MAXIMUM VALUES 5578.01 13438.01 >Enter <cr> to accept parameters or type EXIT:ex > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>gfunc=mixr_mod > GEMPAK-GDLIST>r > > > GDLIST PARAMETERS: > > Grid file: test.gem > > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXR_MOD > > GAREA: dset > SCALE FACTOR : 10** 0 > OUTPUT: TERM/ > > MINIMUM AND MAXIMUM VALUES 5519.52 13429.52 >Enter <cr> to accept parameters or type EXIT:ex > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>gfunc=mixrdiff > GEMPAK-GDLIST>r > > > GDLIST PARAMETERS: > > Grid file: test.gem > > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >860731/1200 2 ZAGL MIXRDIFF > > GAREA: dset > SCALE FACTOR : 10** 0 > OUTPUT: TERM/ > > MINIMUM AND MAXIMUM VALUES -0.55 0.95 >Enter <cr> to accept parameters or type EXIT:ex > Parameters requested: GDATTIM,GLEVEL,GVCORD,GFUNC,GDFILE,GAREA,PROJ,SCALE, > OUTPUT. > GEMPAK-GDLIST>ex >papagayo% > > > >Can you explain what's happening? > >Clint > > > >==================================================================== >Clinton M. Rowe >Associate Professor >Meteorology/Climatology Program phone:(402)472-1946 >Department of Geosciences fax:(402)472-4917 >University of Nebraska-Lincoln address@hidden > >