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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 > >
