19991216: model elevation question

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
>
>