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Hello,
Turns out the math functions are occurring on the data BEFORE it is
interpolated. Hence, at point (x,y) = (8.458,92.63) even though
UREL = -1.116
GFUNC = MUL(urel,urel) gives
MUL(urel,urel) = 3.763
instead of 1.25 because the surrounding 4 gridpoints:
(x,y) UREL VREL
------------- ------------------ --------------
(8,93) (9,93) 1.0634 -2.4366 0.379 1.129
(8,92) (9,92) -1.8116 -2.4366 1.879 -0.371
are each being squared and THEN interpolated. At an exact grid point,
you get the correct/expected answer always.
Though I understand what is going on in the programs, I am still
confused about the vector output. For the same point (8.458,92.63),
the
UREL = UWND = -1.116
VREL = VWND = 0.769
and the program says that
GFUNC = dirn(wnd) = 159.70622
instead of 124.6 degrees (which you get from urel and vrel by using
dirn = 270 - atan2(urel,vrel)*RTD).
What do you think the wind direction should be?
David
On Thu, Nov 24, 2005 at 03:01:07AM -0800, ovens wrote:
> Hello,
>
> I have discovered the following bugs in GEMPAK 5.8.3a (Unidata binary
> version and my compiled and patched versions).
>
> In gdprof and gdpoint the use of MUL(urel,urel) and MAG(WND) and
> DIRN(WND) are giving totally incorrect answers (for ECMWF, GFS, and
> ETA 104 grids at least). When I run MUL(urel,const) I get the
> correct number. This looks like some kind of memory error when both
> arguments are the same item.
>
> Here are the commands and results from gdprof, gdpoint results follow:
> ==================== gdprof results ======================
> GEMPAK-GDPROF>li
> GPOINT = @8.458;92.63
> GDATTIM = f0
> GVCORD = hagl
> GVECT = WND
> GDFILE = /home/disk/data/gempak/model/ecmwf/2005112300_ecmwf.gem
> LINE = 3
> MARKER = 0
> BORDER = 1
> PTYPE = lin
> SCALE = 0
> XAXIS = 0
> YAXIS = 0/10
> WIND = BM1
> REFVEC =
> WINPOS = 1
> FILTER = YES
> TITLE = 1
> PANEL = 0
> CLEAR = YES
> TEXT = 1/21//hw
> DEVICE = XW
> OUTPUT = T
> THTALN = 0
> THTELN = 0
> MIXRLN = 0
> GFUNC = urel
> r
>
>
> Grid function: urel
> X,Y grid point: 8.46 92.63
> Lat/lon: 47.44 -122.31
> Number of levels: 1
> Data range: -1.12 -1.12
> Scaling factor: 10** 0
> 051123/0000V000 UREL @8.458;92.63
> LATITUDE, LONGITUDE = ( 47.44, -122.31 )
> HAGL UREL
> 10.00 -1.116
> HAGL U UREL V VREL
> 10.00 -1.116 0.769
>
> GEMPAK-GDPROF>gfunc = mul(urel,urel)
> GEMPAK-GDPROF>r
> GDPROF PARAMETERS
> Grid function: mul(urel,urel)
> Grid vector function: WND
> X,Y grid point: 8.46 92.63
> Lat/lon: 47.44 -122.31
> Number of levels: 1
> Data range: 3.76 3.76 ***** WRONG!!!!
> Scaling factor: 10** 0
> Wind display: BM1
>
> 051123/0000V000 MULRELUREL @8.458;92.63
> LATITUDE, LONGITUDE = ( 47.44, -122.31 )
> HAGL MULRELUREL
> 10.00 3.763 ***** WRONG!!!!
> HAGL U UREL V VREL
> 10.00 -1.116 0.769
>
> GEMPAK-GDPROF>gfunc = mul(urel,-1.116)
> GEMPAK-GDPROF>r
> Grid function: mul(urel,-1.116)
> Data range: 1.25 1.25
> 051123/0000V000 MULREL-1.1 @8.458;92.63
> LATITUDE, LONGITUDE = ( 47.44, -122.31 )
> HAGL MULREL-1.1
> 10.00 1.246
> HAGL U UREL V VREL
> 10.00 -1.116 0.769
>
>
> ==================== gdpoint results ======================
> GEMPAK-GDPOINT>li
> GDATTIM = f0
> GDFILE = /home/disk/data/gempak/model/ecmwf/2005112300_ecmwf.gem
> GLEVEL = 10
> GPOINT = @8.458;92.63
> GVCORD = hagl
> GFUNC = mul(urel,-1.116)
> SCALE = 0
> GEMPAK-GDPOINT>gfun = urel
> GEMPAK-GDPOINT>r
>
> GDFILE: /home/disk/data/gempak/model/ecmwf/2005112300_ecmw
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : urel
> SCALE : 0
> 051123/0000F000 : -1.11616
>
> GEMPAK-GDPOINT>gfu = mul(urel,urel)
> GEMPAK-GDPOINT>r
> GDFILE: /home/disk/data/gempak/model/ecmwf/2005112300_ecmw
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : mul(urel,urel)
> SCALE : 0
> 051123/0000F000 : 3.76344 ***** WRONG!!!!
> GEMPAK-GDPOINT>gfu = mul(urel,-1.11616)
> GEMPAK-GDPOINT>r
>
> GDFILE: /home/disk/data/gempak/model/ecmwf/2005112300_ecmw
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : mul(urel,-1.11616)
> SCALE : 0
> 051123/0000F000 : 1.24581
> GEMPAK-GDPOINT>gfun = vrel
> GEMPAK-GDPOINT>r
>
> GDFILE: /home/disk/data/gempak/model/ecmwf/2005112300_ecmw
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : vrel
> SCALE : 0
> 051123/0000F000 : 0.76872
>
> GEMPAK-GDPOINT>gfu = mag(wnd)
> GEMPAK-GDPOINT>r
>
> GDFILE: /home/disk/data/gempak/model/ecmwf/2005112300_ecmw
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : mag(wnd)
> SCALE : 0
> 051123/0000F000 : 2.10129 ***** WRONG!!!! s/b 1.355
>
> GEMPAK-GDPOINT>gfu = dirn(wnd)
> GEMPAK-GDPOINT>r
> GFUNC : dirn(wnd)
> 051123/0000F000 : 159.70622 ***** WRONG!!!! s/b 124.6 degrees
>
>
> And, lest you think this is confined to the ecmwf file, here's the
> same bug with the 1-degree GFS file
> GEMPAK-GDPOINT>r
> GDFILE: $HDS/gfs/2005112312_gfs.gem
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : urel
> SCALE : 0
> 051123/1200F000 : -0.83057
> GEMPAK-GDPOINT>gfu = mul(urel,-0.83057)
> GEMPAK-GDPOINT>r
> GFUNC : mul(urel,-0.83057)
> 051123/1200F000 : 0.68985
> GEMPAK-GDPOINT>gfu = mul(urel,urel)
> GEMPAK-GDPOINT>r
> GFUNC : mul(urel,urel)
> 051123/1200F000 : 0.85965 ***** WRONG!!!! s/b 0.689
>
>
> and with the eta104 grids:
> GEMPAK-GDPOINT>gdfi = $HDS/eta/2005112312_eta104.gem
> GEMPAK-GDPOINT>gfu = urel
> GEMPAK-GDPOINT>r
> GDFILE: $HDS/eta/2005112312_eta104.gem
> GPOINT: @8.458;92.63
> GVCORD: hagl
> GLEVEL: 10
> GFUNC : urel
> SCALE : 0
> 051123/1200F000 : -2.27911
> GEMPAK-GDPOINT>gfu= mul(urel,-2.27911)
> GEMPAK-GDPOINT>r
> GFUNC : mul(urel,-2.27911)
> 051123/1200F000 : 5.19433
> Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
> GEMPAK-GDPOINT>gfu = mul(urel,urel)
> GEMPAK-GDPOINT>r
> GFUNC : mul(urel,urel)
> 051123/1200F000 : 5.28800 ***** WRONG!!!! s/b 5.194
>
> GEMPAK-GDPOINT>gfun = vrel
> GEMPAK-GDPOINT>r
> GFUNC : vrel
> 051123/1200F000 : 2.67976
>
> GEMPAK-GDPOINT>gfu = mag(vecr(urel,vrel))
> GEMPAK-GDPOINT>r
> GFUNC : mag(vecr(urel,vrel))
> 051123/1200F000 : 3.58182 ***** WRONG!!!! s/b 3.518
>
> ======================================================================
>
> Thanks in advance for taking a look at this.
>
>
> David
>
> --
> David Ovens e-mail: address@hidden
> Research Meteorologist phone: (206) 685-8108
> Dept of Atm. Sciences plan: Real-time MM5 forecasting for the
> Box 351640 Pacific Northwest
> University of Washington http://www.atmos.washington.edu/mm5rt
> Seattle, WA 98195 Weather Graphics and Loops
> http://www.atmos.washington.edu/~ovens/loops
--
David Ovens e-mail: address@hidden
Research Meteorologist phone: (206) 685-8108
Dept of Atm. Sciences plan: Real-time MM5 forecasting for the
Box 351640 Pacific Northwest
University of Washington http://www.atmos.washington.edu/mm5rt
Seattle, WA 98195 Weather Graphics and Loops
http://www.atmos.washington.edu/~ovens/loops