| 1 | io_grib2 |
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| 2 | |
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| 3 | Author: Todd Hutchinson |
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| 4 | WSI |
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| 5 | thutchinson@wsi.com |
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| 6 | |
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| 7 | 28 September 2005 |
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| 8 | |
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| 9 | I. Introduction |
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| 10 | |
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| 11 | io_grib2 is a WRF module that allows for input and output of WRF data in GRIB |
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| 12 | version 2 format. |
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| 13 | |
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| 14 | Why would anyone use GRIB2 output? |
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| 15 | Data stored in GRIB2 format is compressed using advanced compression |
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| 16 | (i.e., JPEG2000), so output files are much smaller than in other formats |
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| 17 | such as netCDF and grib version 1. Better compression is achieved with |
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| 18 | larger grids. |
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| 19 | |
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| 20 | II. Prerequisites |
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| 21 | |
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| 22 | In order to compile and link WRF using the grib2 format, one system library |
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| 23 | is required: |
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| 24 | libjasper.a: http://www.ece.uvic.ca/~mdadams/jasper/ |
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| 25 | |
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| 26 | The library should be installed in a system accessible place (i.e., |
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| 27 | /usr/lib). The paths to the jasper library and include files must be |
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| 28 | specified via environment variables prior to running ./configure . |
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| 29 | Please use the following environment variables: |
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| 30 | JASPERLIB Path to jasper library files (libjasperlib.a) |
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| 31 | JASPERINC Path to jasper include files |
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| 32 | Note that if these environment variables are not defined before |
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| 33 | ./configure is run, the Grib2 I/O package will not be built. |
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| 34 | |
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| 35 | III. Running WRF with grib2 input/output |
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| 36 | 1. Set namelist entry or entries io_form_<x> to 10 |
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| 37 | 2. Run WRF as you normally would, for example: |
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| 38 | cd test/em_real |
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| 39 | ./real.exe |
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| 40 | ./wrf.exe |
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| 41 | |
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| 42 | IV. Quilting |
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| 43 | If you are running WRF using MPI, you may use a seperate processor for |
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| 44 | quilting just as is done with netCDF. Simply set the namelist variable |
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| 45 | nio_tasks_per_group to 1 (or more). |
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| 46 | |
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| 47 | V. Details |
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| 48 | 1. grib2map.tbl file |
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| 49 | io_grib2 makes use of a table for encoding the WRF data into GRIB2 |
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| 50 | format. The table that io_grib2 uses is contained in the |
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| 51 | WRF run directory, and is called grib2map.tbl. This file is read at |
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| 52 | run-time by io_grib2. Settings in this file are used to encode the |
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| 53 | corresponding parameters in the output files. You may modify |
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| 54 | this file to suit your needs. |
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| 55 | |
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| 56 | The format of the table is described within the file itself. |
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| 57 | |
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| 58 | VI. Comparison between file formats. |
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| 59 | 1. The following table shows the file sizes and run times for netcdf, grib1, |
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| 60 | and grib2 format for a 6 hour simlation of the WRF jun11 test case. The |
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| 61 | domain size in this case is 91x82 by 28 levels. Data was output every |
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| 62 | 3 hours (for a total of 3 output times). The simulations were run on |
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| 63 | NCAR's bluesky system. |
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| 64 | |
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| 65 | | Size (MB) | WRF Time(m:s) |
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| 66 | ------------------------------------ |
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| 67 | NETCDF | 38.40 | 19:31 | |
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| 68 | GRIB1 | 13.42 | 21:22 | |
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| 69 | GRIB2 | 4.33 | 22:36 | |
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| 70 | ------------------------------------ |
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| 71 | |
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| 72 | VII. New namelist variables for Grib2 I/O: |
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| 73 | The following new namelist variables may be optionally used to control |
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| 74 | Grib2 I/O. They are defined in new namelist "&grib2". Note that the |
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| 75 | &grib2 namelist must be included in file "namelist.input" even if empty. |
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| 76 | (This annoyance is ultimately due to problems with old OSF1 Fortran90 |
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| 77 | compilers.) |
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| 78 | |
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| 79 | background_proc_id - Background generating process identifier, typically |
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| 80 | defined by the originating center to identify the background data that |
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| 81 | was used in creating the data. This is octet 13 of Section 4 in the |
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| 82 | grib2 message. Default is 255. |
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| 83 | |
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| 84 | forecast_proc_id - Analysis or generating forecast process identifier, |
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| 85 | typically defined by the originating center to identify the forecast |
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| 86 | process that was used to generate the data. This is octet 14 of Section |
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| 87 | 4 in the grib2 message. Default is 255. |
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| 88 | |
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| 89 | production_status - Production status of processed data in the grib2 |
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| 90 | message. See Code Table 1.3 of the grib2 manual. This is octet 20 of |
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| 91 | Section 1 in the grib2 record. Default is 255. |
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| 92 | |
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| 93 | compression - The compression method to encode the output grib2 message. |
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| 94 | Only 40 for jpeg2000 or 41 for PNG are supported. The default is 40. |
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| 95 | |
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