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How to use GRIB2 data with MM5.

As more and more datasets are moving towards GRIB2, users still making use of MM5 will start running into problems, as MM5 cannot ingest GRIB2 data directly.

Solutions:

1. Convert GRIB2 data to GRIB1, and use as normal in MM5 programs.
   A converter is available from NCEP (http://www.nco.ncep.noaa.gov/pmb/codes/GRIB2/), called cvngrib.
   Note: Limited if any support will be available should MM5 programs not run when using this route.
    
   
2. Use the WRF pre-processing system (WPS) to create intermediate files from GRIB2 datasets directly.
   This is the recommended way to proceed.
   Users only need the UNGRIB section of the WPS programs.
   UNGRIB (from WPS) will REPLACE the pregrid step in the MM5 modeling suite.
   
   
   

Using UNGRID (WPS) in place of pregrid:

Obtain the WPS system from the WRF web site (you need to register to download the code - this is free).

http://www2.mmm.ucar.edu/wrf/users/download/get_source.html

NOTE: From the above page, go to New Users (users will be asked to register - it is free), or Retuning Users (users must supply their email address before they can download the code again).

Configure and Compile WPS

1. Follow the WPS online tutorial. Before you go to the WPS online tutorial, first read the rest of this page. (http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Compile/wps_compile2.htm)
    
2. In general the WRFV2 system needs to be compiled BEFORE WPS can be compiled. But, if only the UNGRIB section of WPS is going to be used, then this is not a problem (if WRFV2 is not compiled before WPS, then the other components of WPS will not compile correctly, but as they are not needed for our purposes, this is not a problem).
    
3. When configuring WPS, an option that supports GRIB2 must be selected. These options require extra libraries (JasPer, PNG and Zlib). Information about these libraries and how to install them are available from the WPS online tutorial.

Run UNGRIB

1. Running instructions are available on this page: http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Basics/UNGRIB/index.html
    
2. Take special note of the WPS namelist. Make sure to set the 'out_format' in the namelist.wps file to 'MM5'. (http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Basics/UNGRIB/ungrib_namelist.htm)
    
3. Running ungrib for MM5 data also requires special Vtables. (Do not use the WPS Vtables, as there are name changes required for MM5.) We have already prepared special MM5 Vtables for NAM and GFS data, which can be used in WPS. Download these before running WPS for MM5 (Vtable.NAM ; Vtable.GFS)
    
4. Note that we have combined the Vtables from the normal 4 into one. So only one intermediate file per time period will be created.

Once you have successfully run ungrib, you can run regridder as per normal, with the FILE:* intermediate files from WPS as input.