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19991216: model elevation question
- Subject: 19991216: model elevation question
- Date: Fri, 17 Dec 1999 10:27:27 -0700
Matt,
All models use some smoothed form of surface data since using
terrain data at a higher resolution than the grid and/or large
discontinuities inadjacent grid point values will cause the model
to blow up with anomalous gravity waves and non-hydrostatic
forcing.
The ETA model employs a step terrain. There are some points about
the difference in actiual station elevation and the model elevation in
the 32km ETA whitepaper at:
http://www.nws.noaa.gov/om/447body.htm
You can also look at the FSL RUC 40km topography at:
http://maps.fsl.noaa.gov/40kmtopocol.gif
They also have ascii 40km and 60km topography datasets for download at:
http://maps.fsl.noaa.gov/MAPS.domain.cgi
We do have a 5 minute (approx 10km) gridded topography dataset for
Gempak which you can use as a gridded data set (eg gdlist, gdpoint etc).
To use the gempak terrain dataset, download from the gbuddy ftp account
nawips-5.4/contrib/terrain.tar.Z
and unpack on your system with:
zcat terrain.tar.Z | tar xvf -
This will create a directory called terrain which containe
the ascii terrain data set (63 Mb) and a program directory called
gdtopo which can be used to convert the data into a gempak
grid file.
First you need to convert the ascii terrain file into a direct access
file (like a gempak map datafile). To do this, you need to build the
tercnvrt program from the fortran code with:
f77 -o tercnvrt tercnvrt.f
Then run tercnvrt to create the direct access file, eg:
prompt% tercnvrt
Please enter name of original terrain dataset: terrain.ascii
^^^^^^^^^^^^^
Now enter name of file which will
contain sector of terrain data: terrain.gsf
^^^^^^^^^^^
Now build and install gdtopo by cd'ing into the gdtopo directory
and building with:
make all
make install
make clean
(This will install the gdtopo program into the $GEMEXE directory and
install the ancillary pdf files as well).
Now you can create a grid file for some area. Since the maximum number of
grid points by default in a gempak grid file is ~97,000 points, this
is approximately 311x311 grid points (for the 5 minute data set this is
roughly 25 degrees x 25 degrees). In otherwords, even though the database
covers the entire globe, you can only view a 25 degree square at a time
as a gempak grid file. As an example, I created a file called us.west
in the terrain subdirectory that is a 20x20 degree file (garea =
25;-125;45;-105) as an example which you can use.
To create your own grid file area, run gdtopo:
GDFILE = us.west
GAREA = 25;-125;45;-105
GDATTIM = 990101/1200
TOPOFL = terrain.gsf
GEMPAK-GDTOPO>r
The gdattim is only used to create a grid time in the output file but
really doesn't do anything else.
An example of running gdcntr with the us.west grid file that is produced:
GDATTIM = 990101/1200
GLEVEL = 0
GVCORD = pres
GFUNC = topo
GDFILE = us.west
CINT = 200
LINE = 5/1/1/0
MAP = 6
TITLE = 1
DEVICE = ps
SATFIL =
RADFIL =
PROJ = ced
GAREA = grid
CLEAR = y
PANEL = 0
TEXT = .5
SCALE = 0
LATLON = 7/10/1//1;1
HILO =
HLSYM =
CLRBAR =
CONTUR = 0
SKIP = 0
FINT = 200
FLINE = 30-7
CTYPE = c
LUTFIL =
STNPLT =
GEMPAK-GDCNTR>r
Creating process: ps for queue 251454
Grid file: us.west
GRID IDENTIFIER:
TIME1 TIME2 LEVL1 LEVL2 VCORD PARM
990101/1200 0 PRES TOPO
GAREA: grid
MINIMUM AND MAXIMUM VALUES -4765.00 3790.00
LINE CONTOURS:
LEVELS: -4600.00 -4400.00 -4200.00 -4000.00 -3800.00 -3600.00 -3400.00
COLORS: 5 5 5 5 5 5 5
LINTYP: 1 1 1 1 1 1 1
LINWID: 1 1 1 1 1 1 1
LABEL: 0 0 0 0 0 0 0
LEVELS: -3200.00 -3000.00 -2800.00 -2600.00 -2400.00 -2200.00 -2000.00
COLORS: 5 5 5 5 5 5 5
LINTYP: 1 1 1 1 1 1 1
LINWID: 1 1 1 1 1 1 1
LABEL: 0 0 0 0 0 0 0
LEVELS: -1800.00 -1600.00 -1400.00 -1200.00 -1000.00 -800.00 -600.00
COLORS: 5 5 5 5 5 5 5
LINTYP: 1 1 1 1 1 1 1
LINWID: 1 1 1 1 1 1 1
LABEL: 0 0 0 0 0 0 0
LEVELS: -400.00 -200.00 0.00 200.00 400.00 600.00 800.00
COLORS: 5 5 5 5 5 5 5
LINTYP: 1 1 1 1 1 1 1
LINWID: 1 1 1 1 1 1 1
LABEL: 0 0 0 0 0 0 0
LEVELS: 1000.00 1200.00 1400.00 1600.00 1800.00 2000.00 2200.00
COLORS: 5 5 5 5 5 5 5
LINTYP: 1 1 1 1 1 1 1
LINWID: 1 1 1 1 1 1 1
LABEL: 0 0 0 0 0 0 0
LEVELS: 2400.00 2600.00 2800.00 3000.00 3200.00 3400.00 3600.00
COLORS: 5 5 5 5 5 5 5
LINTYP: 1 1 1 1 1 1 1
LINWID: 1 1 1 1 1 1 1
LABEL: 0 0 0 0 0 0 0
Enter <cr> to accept parameters or type EXIT:
I hope this helps you with your work.
Steve Chiswell
Unidata User Support
>From: "Matthew G. Fearon" <address@hidden>
>Organization: Desert Research Institute
>Keywords: 199912170024.RAA17299
>Steve,
>
>I attached my question below. I just figure I would mention briefly
>what I am trying to accomplish first.
>
>I have created a text file of 40km eta model hght@0%none field or
>what is consider the ground surface in the eta model. I have done
>this for each grid point for the entire eta grid and each hght has a
>corresponding latitude and longitude. I then compared the true
>ground surface of certain sounding stations to the heights
>from the eta model by locating the closet lat/lon relationship. From
>this comparison, I am noticing that the eta heights are always quite
>higher than the true ground surface of the sounding sites, except for
>FSX which is lower. I attached a list below, the heights are in meters:
>
>stn sounding eta
>RNO 1341.5 1776.8
>UIL 54.880 229.29
>OAK 3.0500 109.45
>FSX 2134.1 1740.0
>EKO 1551.8 1872.2
>BOI 871.95 1371.6
>DEN 1612.8 2238.7
>TUS 786.59 1084.6
>GGW 695.12 832.76
>
>Do you know if there is a prewritten grid file containing the true
>ground
>surface elevation (hgt above mean sea level) that I could match to the
>lat/lons that are available from the 40km eta ?
>
>Your suggestions would be greatly appreciated.
>Thank you in advance,
>
>Matt Fearon
>address@hidden
>
>
