Problems with Grid 104

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ncwxman
Senior Member
Posts: 128
Joined: Sat Aug 07, 2004 12:57 am
Location: North Carolina

Problems with Grid 104

Post by ncwxman »

Jeff,

I have discovered a problem with Grid 104 which is listed in the Grid.dat file as NGM SUPER C-GRID but apparently is also used for other models, in this case the NAM (formerly ETA).

This problem was found in an attempt to view a cross section.

Image

I then ran the ALON command and got the following.

Image

I have also had this problem when working with data that uses Grid 221 (North American Regional Reanalysis).


Thank you,

Kevin

Data sources:

ftpprd.ncep.noaa.gov/pub/data/nccf/com/nam/prod
files used ---> nam.t**z.grbgrd21.tm00

tgftp.nws.noaa.gov/ST.opnl/MT.nam_CY.**/RD.YYYYMMDD/PT.grid_DF.gr1
files used ---> fh.0021_tl.press_gr.grbbgrd

** = Model run -- 00, 06, 12, 18
BLUE number is the forecast hour

Output from the beginning of the NGRB2PCG32.OUT FILE

Code: Select all

FILE: nam.t18z.grbgrd00.tm00                                                  
 ---NEW GRIB DATA FILE OPENED
 ===== BEGIN READ ===== IGB100(           1 &           2) COPIED TO 1 & 2
 GRIB EDITION 1
 ===== BEGIN NEW GRIB EDITION 1 RECORD =====
 REC#,SIZE =            1       26786
  NBYTES,IRDRC7,IRDREC=       26786         267         267
  IRDST/IRDEND/IGRBZZ=           3         266           3
 KPDS=  7 84 104 192 130 102     0   5 10  4 18  0   1   0   0   0   0   1   2
 ACCUM     0    0    0    0 PRSE PRSE
 INPUT YR/MO/DY/HR/FHR/LVL=2005/10/ 4/18/  0/ MSL - PARAM=130  (PRSE MSL)
 GRID DEFINITIONS OBTAINED FROM GRIB GDS SECTION
 ... OUTPUT FILE= c:\PCGRIDDS32\GRIDDATA\OCT040518.ETA104      
 REQUESTED GRID BEING PROCESSED
 --- ADDING GRID->      2 PRSE MSL 2005 10  4 18   0       2
 A,NX,NY=   101177.5        147    110
 GRN,GRX,RANGE=  -22.94989       22.94983      0.2578636    
 --- ADDING GRID->      3 MSG00000 2005 10  4 18   0       7
 A,NX,NY=   1.000000        147    110
 GRN,GRX,RANGE= -1.0000000E-25  9.1084400E-44  5.6179776E-28
 --- ADDING GRID->      4 MSG10000 2005 10  4 18   0      12
 A,NX,NY=  0.0000000E+00    147    110
 GRN,GRX,RANGE= -1.0000000E-25  9.1084400E-44  5.6179776E-28
 MAP PROJECTION =     NPST
 GRID DESCRIPTION SECTION =                    5         147         110
        -268     -139475           8     -105000       90755       90755
           0          64           0           0           0           0
           0           0           0           0         255           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0           0           0           0           0           0
           0
 NPTS =        16170
 GRID PROJECTION TYPE = NPST
 --- ADDING GRID->      5 ALAT0000 2005 10  4 18   0      17
 A,NX,NY= -0.2679985        147    110
 GRN,GRX,RANGE= -0.8700314      0.8700295      9.7756227E-03
 --- ADDING GRID->      6 ALON0000 2005 10  4 18   0      22
 A,NX,NY=   139.4751        147    110
 GRN,GRX,RANGE=  -359.2842       359.7989       4.039793    
 --- ADDING GRID->      7 HGHT0000 2005 10  4 18   0      27
 A,NX,NY=  0.0000000E+00    147    110
 GRN,GRX,RANGE= -1.0000000E-25  9.1084400E-44  5.6179776E-28
 --- ADDING GRID->      8 DMAP0000 2005 10  4 18   0      32
 A,NX,NY=   48407.97        147    110
 GRN,GRX,RANGE=  -480.8623       482.1035       5.409921    
 --- ADDING GRID->      9 FFFF0000 2005 10  4 18   0      37
 A,NX,NY= -1.2968197E-05    147    110
 GRN,GRX,RANGE= -1.4380022E-06  2.5712072E-05  1.5252850E-07
 --- ADDING GRID->     10 EDIR0000 2005 10  4 18   0      42
 A,NX,NY=  -34.47509        147    110
 GRN,GRX,RANGE=  -359.7998       359.2832       4.039793    
 --- ADDING GRID->     11 GRDX0000 2005 10  4 18   0      47
 A,NX,NY=   1.000000        147    110
 GRN,GRX,RANGE=  1.3592595E-43   1.000008      5.6180209E-03
 --- ADDING GRID->     12 GRDY0000 2005 10  4 18   0      52
 A,NX,NY=   1.000000        147    110
 GRN,GRX,RANGE=  1.3592595E-43   1.000008      5.6180209E-03
jkrob
Senior Member
Posts: 300
Joined: Fri Jun 25, 2004 11:42 pm
Contact:

Post by jkrob »

Kevin,

Thanks for all the info but those screen shots were of poor resolution & I'm not sure what the problem is. For the PLAN view, it looks like the grid is a Polar Stereographic projection and the LAT lines are expected to be wavy like that. Now, those two "hooks" in the data are not correct... For the Cross Section, are you refering to how the vertical lines are"bunched" together?

I need to know the command parameters for the PLAN and XSCT commands (the lat - lon data) so I can recreate the displays.

BTW - for screen shots, you may want to reduce your screen resolution to 800x600 or even 640x480 so they will look sharper & I can see everything.

Thanks again,
Jeff
ncwxman
Senior Member
Posts: 128
Joined: Sat Aug 07, 2004 12:57 am
Location: North Carolina

Post by ncwxman »

Jeff,

Sorry for the bad screen shots. I tried to reduce the size of the images in my graphics program but did not turn out like I hoped. I have replaced them in my original post (above).
For the Cross Section, are you refering to how the vertical lines are"bunched" together?
Yes, that is what I am refering to. I believe that this is related to the problem with the wavy long lines seen in plan view. Don't have this problem when using other grids (except the 221).
I need to know the command parameters for the PLAN and XSCT commands (the lat - lon data) so I can recreate the displays.
Plan view:

Code: Select all

loop
PLAN
AREA 35 82 17
endl
Cross section:

Code: Select all

LOOP
TEMP GRTN 400
XSCT 36 84 36 73
TXT4 -----------------------------             
TXT5 This E/W cross section runs -
TXT6 from NE TN TO OFFSHORE      -
TXT7 OF THE NE NC COAST along    -
TXT8 the displayed line below.   -
TXT9 -----------------------------
TXTO -------------------------------------
TXTP Remember you are in Cross Section   -
TXTQ mode, you must type "PLAN" when done-
TXTR to return the program to the normal -
TXTS "planar" mode.                      -
TXTT -------------------------------------
ENDL
Let me know if you need anymore info concerning this. I will be glad to furnish it.

As always, thank you for you work on PCGRIDDS32. It's great!

Kevin
jkrob
Senior Member
Posts: 300
Joined: Fri Jun 25, 2004 11:42 pm
Contact:

Post by jkrob »

Kevin,

Thanks for the extra info. As for the Lon grids...a good example of bad math ;-). The math to calculate longitude points for a NPST is only an approximation (and these are the routines from NCEP!) so the gridpoints come out to look like a stair-step pattern. And if you notice the Lon 75 & 90, the farther south you go the more east the contour line is getting from the map line until at some point, it "rolls over" and is now west of the map line but, again starts drifting east.

This..."feature" has been present since PCGRIDDS and, yes, it is wrong but, it is only affecting the reference data and not the meteorological data. I'll look into it but, like I said, it is very deep math to calculate that and, soon, I'm going to have bigger fish to fry...of which I'll be telling you about shortly.

The best I can say for naow is to calculate the cross section areas away from those stair-step areas on the grid. Go just north or south.

It is odd that the data is NPST when NCEP normally uses Lambert Conformal projections for that part of the earth...Hmmmm.

Thanks again for all the info,
Jeff
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