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19990305: Gridding observational data
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- Subject: 19990305: Gridding observational data
- Date: Fri, 05 Mar 1999 12:52:49 -0700
Rich,
Here are the basic steps for gridding observational data for display
using the gd grid diagnostic programs.
1) create a new grid file with gdcfil
To create a grid file that will hold 1000 grids (maximum is 10,000),
using the grid #211 projection:
GEMPAK-GDCFIL>l
GDOUTF = test.gem
PROJ =
GRDAREA =
KXKY =
MAXGRD = 1000
CPYFIL = #211
ANLYSS =
GEMPAK-GDCFIL>r
Creating process: gplt for queue 1100
GDCFIL PARAMETERS:
New grid file: test.gem
File copied: #211
Grid projection: LCC
Lower left corner: 12.19 -133.46
Upper right corner: 57.29 -49.38
KX, KY: 93 65
DELTAN = 1.000 EXTEND = 0; 0; 0; 0
Maximum number of grids that can be added to file 1000
Enter <cr> to accept parameters or type EXIT:
Parameters requested: GDOUTF,PROJ,GRDAREA,KXKY,MAXGRD,CPYFIL,ANLYSS.
GEMPAK-GDCFIL>
or, to create a 20x20 grid for the LNS area, using a ced projection
GDOUTF = test_lns.gem
PROJ = ced
GRDAREA = lns
KXKY = 20;20
MAXGRD = 1000
CPYFIL =
ANLYSS =
GEMPAK-GDCFIL>r
GDCFIL PARAMETERS:
New grid file: test_lns.gem
Grid projection: CED
Lower left corner: 36.12 -83.30
Upper right corner: 44.12 -69.30
KX, KY: 20 20
X/Y grid spacing: 0.42 0.74
DELTAN = 1.200 EXTEND = 2; 2; 2; 2
Maximum number of grids that can be added to file 1000
Enter <cr> to accept parameters or type EXIT:
Parameters requested: GDOUTF,PROJ,GRDAREA,KXKY,MAXGRD,CPYFIL,ANLYSS.
GEMPAK-GDCFIL>
2) Grid surface data info the resulting grid file using Barnes analysis
using oabsfc (use 2 passes, gamma=.3). ote, gridding surface data will
greate grids with GVCORD = NONE.
SFFILE = $SAO/990305_sao.gem
GDFILE = test.gem
SFPARM = pmsl;tmpc;dwpc;uwnd;vwnd
DATTIM = all
DTAAREA =
GUESS =
GAMMA = .3
SEARCH = 50/EX
NPASS = 2
GEMPAK-OABSFC>r
OABSFC PARAMETERS:
Output grid file: test.gem
Number of x, y points: 93 65
Grid bnds: 12.19 -133.46 57.29 -49.38 Grid xtnd: 0 0 0 0
Station spacing: 1.00
No first guess file is requested.
Surface file: $SAO/990305_sao.gem
Data area: 11.00;-154.00;62.00;-48.00
Parameters: PMSL TMPC DWPC UWND VWND
Time: 990305/0000
GAMMA: 0.30 SEARCH: 50.00 NPASS: 2
Data extrapolation may occur.
Enter <cr> to accept parameters or type EXIT:
RMS values for pass 1
PMSL TMPC DWPC UWND VWND
RMS 1.06 1.86 2.15 2.04 1.95
#STN 1096 1581 1555 1557 1557
RMS values for pass 2
PMSL TMPC DWPC UWND VWND
RMS 0.69 1.33 1.54 1.61 1.51
#STN 1096 1581 1555 1557 1557
OABSFC PARAMETERS:
Output grid file: test.gem
Number of x, y points: 93 65
Grid bnds: 12.19 -133.46 57.29 -49.38 Grid xtnd: 0 0 0 0
Station spacing: 1.00
No first guess file is requested.
Surface file: $SAO/990305_sao.gem
Data area: 11.00;-154.00;62.00;-48.00
Parameters: PMSL TMPC DWPC UWND VWND
Time: 990305/0100
GAMMA: 0.30 SEARCH: 50.00 NPASS: 2
Data extrapolation may occur.
Enter <cr> to accept parameters or type EXIT:
etc....
In the above output, the RMS for each pass is the mean square difference between
the actual data and the interpolated value from the grid. The RMS should
decrease in the second pass (a feature of barnes analysis successive correction
scheme). The number of stations in your grid area that are used for
the anaysis are shown.
3) perform barnes analysis on sounding data using oabsnd.
Note, the number of fields you can grid at one time
depends on how many levels you chose to grid. If you get a message
regarding not enough space to grid all your parameters, decrease
the number of levels, or number of parameters you grid at one time.
SNFILE = $UPA/990305_upa.gem
GDFILE = test.gem
SNPARM = tmpc;dwpc;hght;uwnd;vwnd
STNDEX =
LEVELS = 1000-500-100
VCOORD = pres
DATTIM = all
DTAAREA =
GUESS =
GAMMA = .3
SEARCH = 50/EX
NPASS = 2
GEMPAK-OABSND>r
OABSND PARAMETERS:
Output grid file: test.gem
Number of x, y points: 93 65
Grid bnds: 12.19 -133.46 57.29 -49.38 Grid xtnd: 0 0 0 0
Station spacing: 1.00
No first guess file is requested.
Sounding file: $UPA/990305_upa.gem
Data area: 11.00;-154.00;62.00;-48.00
Level parameters: TMPC DWPC HGHT UWND VWND
Levels: 1000 900 800 700 600 500
Vertical coordinate: pres
Station parameters:
Time: 990305/0000
GAMMA: 0.30 SEARCH: 50.00 NPASS: 2
Data extrapolation may occur.
Enter <cr> to accept parameters or type EXIT:
etc...
4) fields gridded in the test.gem file
GDFILE Grid file test.gem
LSTALL Full list flag yes
OUTPUT Output device/filename t
Parameters requested: GDFILE,LSTALL,OUTPUT.
GEMPAK-GDINFO>r
GRID FILE: test.gem
GRID NAVIGATION:
PROJECTION: LCC
ANGLES: 25.0 -95.0 25.0
GRID SIZE: 93 65
LL CORNER: 12.19 -133.46
UR CORNER: 57.29 -49.38
GRID ANALYSIS BLOCK:
ANALYSIS TYPE: BARNES
DELTAN: 1.000
DELTAX: -9999.000
DELTAY: -9999.000
GRID AREA: 11.00 -154.00 62.00 -48.00
EXTEND AREA: 11.00 -154.00 62.00 -48.00
DATA AREA: 11.00 -154.00 62.00 -48.00
Number of grids in file: 40
Maximum number of grids in file: 1000
NUM TIME1 TIME2 LEVL1 LEVL2 VCORD PARM
1 990305/0000 1000 PRES TMPC
2 990305/0000 1000 PRES DWPC
3 990305/0000 1000 PRES HGHT
4 990305/0000 1000 PRES UWND
5 990305/0000 1000 PRES VWND
6 990305/0000 900 PRES TMPC
7 990305/0000 900 PRES DWPC
8 990305/0000 900 PRES HGHT
9 990305/0000 900 PRES UWND
10 990305/0000 900 PRES VWND
11 990305/0000 800 PRES TMPC
12 990305/0000 800 PRES DWPC
13 990305/0000 800 PRES HGHT
14 990305/0000 800 PRES UWND
15 990305/0000 800 PRES VWND
16 990305/0000 700 PRES TMPC
17 990305/0000 700 PRES DWPC
18 990305/0000 700 PRES HGHT
19 990305/0000 700 PRES UWND
20 990305/0000 700 PRES VWND
21 990305/0000 600 PRES TMPC
22 990305/0000 600 PRES DWPC
23 990305/0000 600 PRES HGHT
24 990305/0000 600 PRES UWND
25 990305/0000 600 PRES VWND
26 990305/0000 500 PRES TMPC
27 990305/0000 500 PRES DWPC
28 990305/0000 500 PRES HGHT
29 990305/0000 500 PRES UWND
30 990305/0000 500 PRES VWND
31 990305/0000 0 NONE PMSL
32 990305/0000 0 NONE TMPC
33 990305/0000 0 NONE DWPC
34 990305/0000 0 NONE UWND
35 990305/0000 0 NONE VWND
36 990305/0100 0 NONE PMSL
37 990305/0100 0 NONE TMPC
38 990305/0100 0 NONE DWPC
39 990305/0100 0 NONE UWND
40 990305/0100 0 NONE VWND
Parameters requested: GDFILE,LSTALL,OUTPUT.
GEMPAK-GDINFO>
I also have examples on gridding data, complete with exercises at:
http://www.unidata.ucar.edu/packages/gempak/tutorial/barnes.html
The one program I haven't mentioned above is called "oagrid".
Oagrid is a program similar to gdcfil, in that it will create
the grid file that you will write the barnes analyzed grids into.
The difference between oagrid and gdcfil is that in gdcfil, you
tell the program what projection, grid area and number of gridpoints
you will use.
In Oagrid, you ask the program to look at your observed data (surface or
upper air data), and the program will create a CED grid for your
area with a suggested mean station spacing based on the observed data.
You can only create CED grids with OAGRID, but it is useful to
suggest a mean gridpoint spacing based on your data if you don't
have much experience with objective analysis.
Steve Chiswell
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